oikos/web/node_modules/graphology/dist/graphology.umd.js

(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
  typeof define === 'function' && define.amd ? define(factory) :
  (global = typeof globalThis !== 'undefined' ? globalThis : global || self, global.graphology = factory());
})(this, (function () { 'use strict';

  function _assertThisInitialized(e) {
    if (void 0 === e) throw new ReferenceError("this hasn't been initialised - super() hasn't been called");
    return e;
  }
  function _construct(t, e, r) {
    if (_isNativeReflectConstruct()) return Reflect.construct.apply(null, arguments);
    var o = [null];
    o.push.apply(o, e);
    var p = new (t.bind.apply(t, o))();
    return r && _setPrototypeOf(p, r.prototype), p;
  }
  function _defineProperty(e, r, t) {
    return (r = _toPropertyKey(r)) in e ? Object.defineProperty(e, r, {
      value: t,
      enumerable: !0,
      configurable: !0,
      writable: !0
    }) : e[r] = t, e;
  }
  function _getPrototypeOf(t) {
    return _getPrototypeOf = Object.setPrototypeOf ? Object.getPrototypeOf.bind() : function (t) {
      return t.__proto__ || Object.getPrototypeOf(t);
    }, _getPrototypeOf(t);
  }
  function _inheritsLoose(t, o) {
    t.prototype = Object.create(o.prototype), t.prototype.constructor = t, _setPrototypeOf(t, o);
  }
  function _isNativeFunction(t) {
    try {
      return -1 !== Function.toString.call(t).indexOf("[native code]");
    } catch (n) {
      return "function" == typeof t;
    }
  }
  function _isNativeReflectConstruct() {
    try {
      var t = !Boolean.prototype.valueOf.call(Reflect.construct(Boolean, [], function () {}));
    } catch (t) {}
    return (_isNativeReflectConstruct = function () {
      return !!t;
    })();
  }
  function _setPrototypeOf(t, e) {
    return _setPrototypeOf = Object.setPrototypeOf ? Object.setPrototypeOf.bind() : function (t, e) {
      return t.__proto__ = e, t;
    }, _setPrototypeOf(t, e);
  }
  function _toPrimitive(t, r) {
    if ("object" != typeof t || !t) return t;
    var e = t[Symbol.toPrimitive];
    if (void 0 !== e) {
      var i = e.call(t, r || "default");
      if ("object" != typeof i) return i;
      throw new TypeError("@@toPrimitive must return a primitive value.");
    }
    return ("string" === r ? String : Number)(t);
  }
  function _toPropertyKey(t) {
    var i = _toPrimitive(t, "string");
    return "symbol" == typeof i ? i : i + "";
  }
  function _typeof(o) {
    "@babel/helpers - typeof";

    return _typeof = "function" == typeof Symbol && "symbol" == typeof Symbol.iterator ? function (o) {
      return typeof o;
    } : function (o) {
      return o && "function" == typeof Symbol && o.constructor === Symbol && o !== Symbol.prototype ? "symbol" : typeof o;
    }, _typeof(o);
  }
  function _wrapNativeSuper(t) {
    var r = "function" == typeof Map ? new Map() : void 0;
    return _wrapNativeSuper = function (t) {
      if (null === t || !_isNativeFunction(t)) return t;
      if ("function" != typeof t) throw new TypeError("Super expression must either be null or a function");
      if (void 0 !== r) {
        if (r.has(t)) return r.get(t);
        r.set(t, Wrapper);
      }
      function Wrapper() {
        return _construct(t, arguments, _getPrototypeOf(this).constructor);
      }
      return Wrapper.prototype = Object.create(t.prototype, {
        constructor: {
          value: Wrapper,
          enumerable: !1,
          writable: !0,
          configurable: !0
        }
      }), _setPrototypeOf(Wrapper, t);
    }, _wrapNativeSuper(t);
  }

  /**
   * Graphology Utilities
   * =====================
   *
   * Collection of helpful functions used by the implementation.
   */

  /**
   * Object.assign-like polyfill.
   *
   * @param  {object} target       - First object.
   * @param  {object} [...objects] - Objects to merge.
   * @return {object}
   */
  function assignPolyfill() {
    var target = arguments[0];
    for (var i = 1, l = arguments.length; i < l; i++) {
      if (!arguments[i]) continue;
      for (var k in arguments[i]) target[k] = arguments[i][k];
    }
    return target;
  }
  var assign = assignPolyfill;
  if (typeof Object.assign === 'function') assign = Object.assign;

  /**
   * Function returning the first matching edge for given path.
   * Note: this function does not check the existence of source & target. This
   * must be performed by the caller.
   *
   * @param  {Graph}  graph  - Target graph.
   * @param  {any}    source - Source node.
   * @param  {any}    target - Target node.
   * @param  {string} type   - Type of the edge (mixed, directed or undirected).
   * @return {string|null}
   */
  function getMatchingEdge(graph, source, target, type) {
    var sourceData = graph._nodes.get(source);
    var edge = null;
    if (!sourceData) return edge;
    if (type === 'mixed') {
      edge = sourceData.out && sourceData.out[target] || sourceData.undirected && sourceData.undirected[target];
    } else if (type === 'directed') {
      edge = sourceData.out && sourceData.out[target];
    } else {
      edge = sourceData.undirected && sourceData.undirected[target];
    }
    return edge;
  }

  /**
   * Checks whether the given value is a plain object.
   *
   * @param  {mixed}   value - Target value.
   * @return {boolean}
   */
  function isPlainObject(value) {
    // NOTE: as per https://github.com/graphology/graphology/issues/149
    // this function has been loosened not to reject object instances
    // coming from other JavaScript contexts. It has also been chosen
    // not to improve it to avoid obvious false positives and avoid
    // taking a performance hit. People should really use TypeScript
    // if they want to avoid feeding subtly irrelvant attribute objects.
    return _typeof(value) === 'object' && value !== null;
  }

  /**
   * Checks whether the given object is empty.
   *
   * @param  {object}  o - Target Object.
   * @return {boolean}
   */
  function isEmpty(o) {
    var k;
    for (k in o) return false;
    return true;
  }

  /**
   * Creates a "private" property for the given member name by concealing it
   * using the `enumerable` option.
   *
   * @param {object} target - Target object.
   * @param {string} name   - Member name.
   */
  function privateProperty(target, name, value) {
    Object.defineProperty(target, name, {
      enumerable: false,
      configurable: false,
      writable: true,
      value: value
    });
  }

  /**
   * Creates a read-only property for the given member name & the given getter.
   *
   * @param {object}   target - Target object.
   * @param {string}   name   - Member name.
   * @param {mixed}    value  - The attached getter or fixed value.
   */
  function readOnlyProperty(target, name, value) {
    var descriptor = {
      enumerable: true,
      configurable: true
    };
    if (typeof value === 'function') {
      descriptor.get = value;
    } else {
      descriptor.value = value;
      descriptor.writable = false;
    }
    Object.defineProperty(target, name, descriptor);
  }

  /**
   * Returns whether the given object constitute valid hints.
   *
   * @param {object} hints - Target object.
   */
  function validateHints(hints) {
    if (!isPlainObject(hints)) return false;
    if (hints.attributes && !Array.isArray(hints.attributes)) return false;
    return true;
  }

  /**
   * Creates a function generating incremental ids for edges.
   *
   * @return {function}
   */
  function incrementalIdStartingFromRandomByte() {
    var i = Math.floor(Math.random() * 256) & 0xff;
    return function () {
      return i++;
    };
  }

  /**
   * Chains multiple iterators into a single iterator.
   *
   * @param {...Iterator} iterables
   * @returns {Iterator}
   */
  function chain() {
    var iterables = arguments;
    var current = null;
    var i = -1;
    return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
      return this;
    }), "next", function next() {
      var step = null;
      do {
        if (current === null) {
          i++;
          if (i >= iterables.length) return {
            done: true
          };
          current = iterables[i][Symbol.iterator]();
        }
        step = current.next();
        if (step.done) {
          current = null;
          continue;
        }
        break;
        // eslint-disable-next-line no-constant-condition
      } while (true);
      return step;
    });
  }
  function emptyIterator() {
    return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
      return this;
    }), "next", function next() {
      return {
        done: true
      };
    });
  }

  var events = {exports: {}};

  var R = typeof Reflect === 'object' ? Reflect : null;
  var ReflectApply = R && typeof R.apply === 'function' ? R.apply : function ReflectApply(target, receiver, args) {
    return Function.prototype.apply.call(target, receiver, args);
  };
  var ReflectOwnKeys;
  if (R && typeof R.ownKeys === 'function') {
    ReflectOwnKeys = R.ownKeys;
  } else if (Object.getOwnPropertySymbols) {
    ReflectOwnKeys = function ReflectOwnKeys(target) {
      return Object.getOwnPropertyNames(target).concat(Object.getOwnPropertySymbols(target));
    };
  } else {
    ReflectOwnKeys = function ReflectOwnKeys(target) {
      return Object.getOwnPropertyNames(target);
    };
  }
  function ProcessEmitWarning(warning) {
    if (console && console.warn) console.warn(warning);
  }
  var NumberIsNaN = Number.isNaN || function NumberIsNaN(value) {
    return value !== value;
  };
  function EventEmitter() {
    EventEmitter.init.call(this);
  }
  events.exports = EventEmitter;
  events.exports.once = once;

  // Backwards-compat with node 0.10.x
  EventEmitter.EventEmitter = EventEmitter;
  EventEmitter.prototype._events = undefined;
  EventEmitter.prototype._eventsCount = 0;
  EventEmitter.prototype._maxListeners = undefined;

  // By default EventEmitters will print a warning if more than 10 listeners are
  // added to it. This is a useful default which helps finding memory leaks.
  var defaultMaxListeners = 10;
  function checkListener(listener) {
    if (typeof listener !== 'function') {
      throw new TypeError('The "listener" argument must be of type Function. Received type ' + typeof listener);
    }
  }
  Object.defineProperty(EventEmitter, 'defaultMaxListeners', {
    enumerable: true,
    get: function () {
      return defaultMaxListeners;
    },
    set: function (arg) {
      if (typeof arg !== 'number' || arg < 0 || NumberIsNaN(arg)) {
        throw new RangeError('The value of "defaultMaxListeners" is out of range. It must be a non-negative number. Received ' + arg + '.');
      }
      defaultMaxListeners = arg;
    }
  });
  EventEmitter.init = function () {
    if (this._events === undefined || this._events === Object.getPrototypeOf(this)._events) {
      this._events = Object.create(null);
      this._eventsCount = 0;
    }
    this._maxListeners = this._maxListeners || undefined;
  };

  // Obviously not all Emitters should be limited to 10. This function allows
  // that to be increased. Set to zero for unlimited.
  EventEmitter.prototype.setMaxListeners = function setMaxListeners(n) {
    if (typeof n !== 'number' || n < 0 || NumberIsNaN(n)) {
      throw new RangeError('The value of "n" is out of range. It must be a non-negative number. Received ' + n + '.');
    }
    this._maxListeners = n;
    return this;
  };
  function _getMaxListeners(that) {
    if (that._maxListeners === undefined) return EventEmitter.defaultMaxListeners;
    return that._maxListeners;
  }
  EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
    return _getMaxListeners(this);
  };
  EventEmitter.prototype.emit = function emit(type) {
    var args = [];
    for (var i = 1; i < arguments.length; i++) args.push(arguments[i]);
    var doError = type === 'error';
    var events = this._events;
    if (events !== undefined) doError = doError && events.error === undefined;else if (!doError) return false;

    // If there is no 'error' event listener then throw.
    if (doError) {
      var er;
      if (args.length > 0) er = args[0];
      if (er instanceof Error) {
        // Note: The comments on the `throw` lines are intentional, they show
        // up in Node's output if this results in an unhandled exception.
        throw er; // Unhandled 'error' event
      }
      // At least give some kind of context to the user
      var err = new Error('Unhandled error.' + (er ? ' (' + er.message + ')' : ''));
      err.context = er;
      throw err; // Unhandled 'error' event
    }
    var handler = events[type];
    if (handler === undefined) return false;
    if (typeof handler === 'function') {
      ReflectApply(handler, this, args);
    } else {
      var len = handler.length;
      var listeners = arrayClone(handler, len);
      for (var i = 0; i < len; ++i) ReflectApply(listeners[i], this, args);
    }
    return true;
  };
  function _addListener(target, type, listener, prepend) {
    var m;
    var events;
    var existing;
    checkListener(listener);
    events = target._events;
    if (events === undefined) {
      events = target._events = Object.create(null);
      target._eventsCount = 0;
    } else {
      // To avoid recursion in the case that type === "newListener"! Before
      // adding it to the listeners, first emit "newListener".
      if (events.newListener !== undefined) {
        target.emit('newListener', type, listener.listener ? listener.listener : listener);

        // Re-assign `events` because a newListener handler could have caused the
        // this._events to be assigned to a new object
        events = target._events;
      }
      existing = events[type];
    }
    if (existing === undefined) {
      // Optimize the case of one listener. Don't need the extra array object.
      existing = events[type] = listener;
      ++target._eventsCount;
    } else {
      if (typeof existing === 'function') {
        // Adding the second element, need to change to array.
        existing = events[type] = prepend ? [listener, existing] : [existing, listener];
        // If we've already got an array, just append.
      } else if (prepend) {
        existing.unshift(listener);
      } else {
        existing.push(listener);
      }

      // Check for listener leak
      m = _getMaxListeners(target);
      if (m > 0 && existing.length > m && !existing.warned) {
        existing.warned = true;
        // No error code for this since it is a Warning
        // eslint-disable-next-line no-restricted-syntax
        var w = new Error('Possible EventEmitter memory leak detected. ' + existing.length + ' ' + String(type) + ' listeners ' + 'added. Use emitter.setMaxListeners() to ' + 'increase limit');
        w.name = 'MaxListenersExceededWarning';
        w.emitter = target;
        w.type = type;
        w.count = existing.length;
        ProcessEmitWarning(w);
      }
    }
    return target;
  }
  EventEmitter.prototype.addListener = function addListener(type, listener) {
    return _addListener(this, type, listener, false);
  };
  EventEmitter.prototype.on = EventEmitter.prototype.addListener;
  EventEmitter.prototype.prependListener = function prependListener(type, listener) {
    return _addListener(this, type, listener, true);
  };
  function onceWrapper() {
    if (!this.fired) {
      this.target.removeListener(this.type, this.wrapFn);
      this.fired = true;
      if (arguments.length === 0) return this.listener.call(this.target);
      return this.listener.apply(this.target, arguments);
    }
  }
  function _onceWrap(target, type, listener) {
    var state = {
      fired: false,
      wrapFn: undefined,
      target: target,
      type: type,
      listener: listener
    };
    var wrapped = onceWrapper.bind(state);
    wrapped.listener = listener;
    state.wrapFn = wrapped;
    return wrapped;
  }
  EventEmitter.prototype.once = function once(type, listener) {
    checkListener(listener);
    this.on(type, _onceWrap(this, type, listener));
    return this;
  };
  EventEmitter.prototype.prependOnceListener = function prependOnceListener(type, listener) {
    checkListener(listener);
    this.prependListener(type, _onceWrap(this, type, listener));
    return this;
  };

  // Emits a 'removeListener' event if and only if the listener was removed.
  EventEmitter.prototype.removeListener = function removeListener(type, listener) {
    var list, events, position, i, originalListener;
    checkListener(listener);
    events = this._events;
    if (events === undefined) return this;
    list = events[type];
    if (list === undefined) return this;
    if (list === listener || list.listener === listener) {
      if (--this._eventsCount === 0) this._events = Object.create(null);else {
        delete events[type];
        if (events.removeListener) this.emit('removeListener', type, list.listener || listener);
      }
    } else if (typeof list !== 'function') {
      position = -1;
      for (i = list.length - 1; i >= 0; i--) {
        if (list[i] === listener || list[i].listener === listener) {
          originalListener = list[i].listener;
          position = i;
          break;
        }
      }
      if (position < 0) return this;
      if (position === 0) list.shift();else {
        spliceOne(list, position);
      }
      if (list.length === 1) events[type] = list[0];
      if (events.removeListener !== undefined) this.emit('removeListener', type, originalListener || listener);
    }
    return this;
  };
  EventEmitter.prototype.off = EventEmitter.prototype.removeListener;
  EventEmitter.prototype.removeAllListeners = function removeAllListeners(type) {
    var listeners, events, i;
    events = this._events;
    if (events === undefined) return this;

    // not listening for removeListener, no need to emit
    if (events.removeListener === undefined) {
      if (arguments.length === 0) {
        this._events = Object.create(null);
        this._eventsCount = 0;
      } else if (events[type] !== undefined) {
        if (--this._eventsCount === 0) this._events = Object.create(null);else delete events[type];
      }
      return this;
    }

    // emit removeListener for all listeners on all events
    if (arguments.length === 0) {
      var keys = Object.keys(events);
      var key;
      for (i = 0; i < keys.length; ++i) {
        key = keys[i];
        if (key === 'removeListener') continue;
        this.removeAllListeners(key);
      }
      this.removeAllListeners('removeListener');
      this._events = Object.create(null);
      this._eventsCount = 0;
      return this;
    }
    listeners = events[type];
    if (typeof listeners === 'function') {
      this.removeListener(type, listeners);
    } else if (listeners !== undefined) {
      // LIFO order
      for (i = listeners.length - 1; i >= 0; i--) {
        this.removeListener(type, listeners[i]);
      }
    }
    return this;
  };
  function _listeners(target, type, unwrap) {
    var events = target._events;
    if (events === undefined) return [];
    var evlistener = events[type];
    if (evlistener === undefined) return [];
    if (typeof evlistener === 'function') return unwrap ? [evlistener.listener || evlistener] : [evlistener];
    return unwrap ? unwrapListeners(evlistener) : arrayClone(evlistener, evlistener.length);
  }
  EventEmitter.prototype.listeners = function listeners(type) {
    return _listeners(this, type, true);
  };
  EventEmitter.prototype.rawListeners = function rawListeners(type) {
    return _listeners(this, type, false);
  };
  EventEmitter.listenerCount = function (emitter, type) {
    if (typeof emitter.listenerCount === 'function') {
      return emitter.listenerCount(type);
    } else {
      return listenerCount.call(emitter, type);
    }
  };
  EventEmitter.prototype.listenerCount = listenerCount;
  function listenerCount(type) {
    var events = this._events;
    if (events !== undefined) {
      var evlistener = events[type];
      if (typeof evlistener === 'function') {
        return 1;
      } else if (evlistener !== undefined) {
        return evlistener.length;
      }
    }
    return 0;
  }
  EventEmitter.prototype.eventNames = function eventNames() {
    return this._eventsCount > 0 ? ReflectOwnKeys(this._events) : [];
  };
  function arrayClone(arr, n) {
    var copy = new Array(n);
    for (var i = 0; i < n; ++i) copy[i] = arr[i];
    return copy;
  }
  function spliceOne(list, index) {
    for (; index + 1 < list.length; index++) list[index] = list[index + 1];
    list.pop();
  }
  function unwrapListeners(arr) {
    var ret = new Array(arr.length);
    for (var i = 0; i < ret.length; ++i) {
      ret[i] = arr[i].listener || arr[i];
    }
    return ret;
  }
  function once(emitter, name) {
    return new Promise(function (resolve, reject) {
      function errorListener(err) {
        emitter.removeListener(name, resolver);
        reject(err);
      }
      function resolver() {
        if (typeof emitter.removeListener === 'function') {
          emitter.removeListener('error', errorListener);
        }
        resolve([].slice.call(arguments));
      }
      eventTargetAgnosticAddListener(emitter, name, resolver, {
        once: true
      });
      if (name !== 'error') {
        addErrorHandlerIfEventEmitter(emitter, errorListener, {
          once: true
        });
      }
    });
  }
  function addErrorHandlerIfEventEmitter(emitter, handler, flags) {
    if (typeof emitter.on === 'function') {
      eventTargetAgnosticAddListener(emitter, 'error', handler, flags);
    }
  }
  function eventTargetAgnosticAddListener(emitter, name, listener, flags) {
    if (typeof emitter.on === 'function') {
      if (flags.once) {
        emitter.once(name, listener);
      } else {
        emitter.on(name, listener);
      }
    } else if (typeof emitter.addEventListener === 'function') {
      // EventTarget does not have `error` event semantics like Node
      // EventEmitters, we do not listen for `error` events here.
      emitter.addEventListener(name, function wrapListener(arg) {
        // IE does not have builtin `{ once: true }` support so we
        // have to do it manually.
        if (flags.once) {
          emitter.removeEventListener(name, wrapListener);
        }
        listener(arg);
      });
    } else {
      throw new TypeError('The "emitter" argument must be of type EventEmitter. Received type ' + typeof emitter);
    }
  }

  /**
   * Graphology Custom Errors
   * =========================
   *
   * Defining custom errors for ease of use & easy unit tests across
   * implementations (normalized typology rather than relying on error
   * messages to check whether the correct error was found).
   */
  var GraphError = /*#__PURE__*/function (_Error) {
    _inheritsLoose(GraphError, _Error);
    function GraphError(message) {
      var _this;
      _this = _Error.call(this) || this;
      _this.name = 'GraphError';
      _this.message = message;
      return _this;
    }
    return GraphError;
  }( /*#__PURE__*/_wrapNativeSuper(Error));
  var InvalidArgumentsGraphError = /*#__PURE__*/function (_GraphError) {
    _inheritsLoose(InvalidArgumentsGraphError, _GraphError);
    function InvalidArgumentsGraphError(message) {
      var _this2;
      _this2 = _GraphError.call(this, message) || this;
      _this2.name = 'InvalidArgumentsGraphError';

      // This is V8 specific to enhance stack readability
      if (typeof Error.captureStackTrace === 'function') Error.captureStackTrace(_assertThisInitialized(_this2), InvalidArgumentsGraphError.prototype.constructor);
      return _this2;
    }
    return InvalidArgumentsGraphError;
  }(GraphError);
  var NotFoundGraphError = /*#__PURE__*/function (_GraphError2) {
    _inheritsLoose(NotFoundGraphError, _GraphError2);
    function NotFoundGraphError(message) {
      var _this3;
      _this3 = _GraphError2.call(this, message) || this;
      _this3.name = 'NotFoundGraphError';

      // This is V8 specific to enhance stack readability
      if (typeof Error.captureStackTrace === 'function') Error.captureStackTrace(_assertThisInitialized(_this3), NotFoundGraphError.prototype.constructor);
      return _this3;
    }
    return NotFoundGraphError;
  }(GraphError);
  var UsageGraphError = /*#__PURE__*/function (_GraphError3) {
    _inheritsLoose(UsageGraphError, _GraphError3);
    function UsageGraphError(message) {
      var _this4;
      _this4 = _GraphError3.call(this, message) || this;
      _this4.name = 'UsageGraphError';

      // This is V8 specific to enhance stack readability
      if (typeof Error.captureStackTrace === 'function') Error.captureStackTrace(_assertThisInitialized(_this4), UsageGraphError.prototype.constructor);
      return _this4;
    }
    return UsageGraphError;
  }(GraphError);

  /**
   * Graphology Internal Data Classes
   * =================================
   *
   * Internal classes hopefully reduced to structs by engines & storing
   * necessary information for nodes & edges.
   *
   * Note that those classes don't rely on the `class` keyword to avoid some
   * cruft introduced by most of ES2015 transpilers.
   */

  /**
   * MixedNodeData class.
   *
   * @constructor
   * @param {string} string     - The node's key.
   * @param {object} attributes - Node's attributes.
   */
  function MixedNodeData(key, attributes) {
    // Attributes
    this.key = key;
    this.attributes = attributes;
    this.clear();
  }
  MixedNodeData.prototype.clear = function () {
    // Degrees
    this.inDegree = 0;
    this.outDegree = 0;
    this.undirectedDegree = 0;
    this.undirectedLoops = 0;
    this.directedLoops = 0;

    // Indices
    this["in"] = {};
    this.out = {};
    this.undirected = {};
  };

  /**
   * DirectedNodeData class.
   *
   * @constructor
   * @param {string} string     - The node's key.
   * @param {object} attributes - Node's attributes.
   */
  function DirectedNodeData(key, attributes) {
    // Attributes
    this.key = key;
    this.attributes = attributes;
    this.clear();
  }
  DirectedNodeData.prototype.clear = function () {
    // Degrees
    this.inDegree = 0;
    this.outDegree = 0;
    this.directedLoops = 0;

    // Indices
    this["in"] = {};
    this.out = {};
  };

  /**
   * UndirectedNodeData class.
   *
   * @constructor
   * @param {string} string     - The node's key.
   * @param {object} attributes - Node's attributes.
   */
  function UndirectedNodeData(key, attributes) {
    // Attributes
    this.key = key;
    this.attributes = attributes;
    this.clear();
  }
  UndirectedNodeData.prototype.clear = function () {
    // Degrees
    this.undirectedDegree = 0;
    this.undirectedLoops = 0;

    // Indices
    this.undirected = {};
  };

  /**
   * EdgeData class.
   *
   * @constructor
   * @param {boolean} undirected   - Whether the edge is undirected.
   * @param {string}  string       - The edge's key.
   * @param {string}  source       - Source of the edge.
   * @param {string}  target       - Target of the edge.
   * @param {object}  attributes   - Edge's attributes.
   */
  function EdgeData(undirected, key, source, target, attributes) {
    // Attributes
    this.key = key;
    this.attributes = attributes;
    this.undirected = undirected;

    // Extremities
    this.source = source;
    this.target = target;
  }
  EdgeData.prototype.attach = function () {
    var outKey = 'out';
    var inKey = 'in';
    if (this.undirected) outKey = inKey = 'undirected';
    var source = this.source.key;
    var target = this.target.key;

    // Handling source
    this.source[outKey][target] = this;
    if (this.undirected && source === target) return;

    // Handling target
    this.target[inKey][source] = this;
  };
  EdgeData.prototype.attachMulti = function () {
    var outKey = 'out';
    var inKey = 'in';
    var source = this.source.key;
    var target = this.target.key;
    if (this.undirected) outKey = inKey = 'undirected';

    // Handling source
    var adj = this.source[outKey];
    var head = adj[target];
    if (typeof head === 'undefined') {
      adj[target] = this;

      // Self-loop optimization
      if (!(this.undirected && source === target)) {
        // Handling target
        this.target[inKey][source] = this;
      }
      return;
    }

    // Prepending to doubly-linked list
    head.previous = this;
    this.next = head;

    // Pointing to new head
    // NOTE: use mutating swap later to avoid lookup?
    adj[target] = this;
    this.target[inKey][source] = this;
  };
  EdgeData.prototype.detach = function () {
    var source = this.source.key;
    var target = this.target.key;
    var outKey = 'out';
    var inKey = 'in';
    if (this.undirected) outKey = inKey = 'undirected';
    delete this.source[outKey][target];

    // No-op delete in case of undirected self-loop
    delete this.target[inKey][source];
  };
  EdgeData.prototype.detachMulti = function () {
    var source = this.source.key;
    var target = this.target.key;
    var outKey = 'out';
    var inKey = 'in';
    if (this.undirected) outKey = inKey = 'undirected';

    // Deleting from doubly-linked list
    if (this.previous === undefined) {
      // We are dealing with the head

      // Should we delete the adjacency entry because it is now empty?
      if (this.next === undefined) {
        delete this.source[outKey][target];

        // No-op delete in case of undirected self-loop
        delete this.target[inKey][source];
      } else {
        // Detaching
        this.next.previous = undefined;

        // NOTE: could avoid the lookups by creating a #.become mutating method
        this.source[outKey][target] = this.next;

        // No-op delete in case of undirected self-loop
        this.target[inKey][source] = this.next;
      }
    } else {
      // We are dealing with another list node
      this.previous.next = this.next;

      // If not last
      if (this.next !== undefined) {
        this.next.previous = this.previous;
      }
    }
  };

  /**
   * Graphology Node Attributes methods
   * ===================================
   */
  var NODE = 0;
  var SOURCE = 1;
  var TARGET = 2;
  var OPPOSITE = 3;
  function findRelevantNodeData(graph, method, mode, nodeOrEdge, nameOrEdge, add1, add2) {
    var nodeData, edgeData, arg1, arg2;
    nodeOrEdge = '' + nodeOrEdge;
    if (mode === NODE) {
      nodeData = graph._nodes.get(nodeOrEdge);
      if (!nodeData) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(nodeOrEdge, "\" node in the graph."));
      arg1 = nameOrEdge;
      arg2 = add1;
    } else if (mode === OPPOSITE) {
      nameOrEdge = '' + nameOrEdge;
      edgeData = graph._edges.get(nameOrEdge);
      if (!edgeData) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(nameOrEdge, "\" edge in the graph."));
      var source = edgeData.source.key;
      var target = edgeData.target.key;
      if (nodeOrEdge === source) {
        nodeData = edgeData.target;
      } else if (nodeOrEdge === target) {
        nodeData = edgeData.source;
      } else {
        throw new NotFoundGraphError("Graph.".concat(method, ": the \"").concat(nodeOrEdge, "\" node is not attached to the \"").concat(nameOrEdge, "\" edge (").concat(source, ", ").concat(target, ")."));
      }
      arg1 = add1;
      arg2 = add2;
    } else {
      edgeData = graph._edges.get(nodeOrEdge);
      if (!edgeData) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(nodeOrEdge, "\" edge in the graph."));
      if (mode === SOURCE) {
        nodeData = edgeData.source;
      } else {
        nodeData = edgeData.target;
      }
      arg1 = nameOrEdge;
      arg2 = add1;
    }
    return [nodeData, arg1, arg2];
  }
  function attachNodeAttributeGetter(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1) {
      var _findRelevantNodeData = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1),
        data = _findRelevantNodeData[0],
        name = _findRelevantNodeData[1];
      return data.attributes[name];
    };
  }
  function attachNodeAttributesGetter(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge) {
      var _findRelevantNodeData2 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge),
        data = _findRelevantNodeData2[0];
      return data.attributes;
    };
  }
  function attachNodeAttributeChecker(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1) {
      var _findRelevantNodeData3 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1),
        data = _findRelevantNodeData3[0],
        name = _findRelevantNodeData3[1];
      return data.attributes.hasOwnProperty(name);
    };
  }
  function attachNodeAttributeSetter(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1, add2) {
      var _findRelevantNodeData4 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1, add2),
        data = _findRelevantNodeData4[0],
        name = _findRelevantNodeData4[1],
        value = _findRelevantNodeData4[2];
      data.attributes[name] = value;

      // Emitting
      this.emit('nodeAttributesUpdated', {
        key: data.key,
        type: 'set',
        attributes: data.attributes,
        name: name
      });
      return this;
    };
  }
  function attachNodeAttributeUpdater(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1, add2) {
      var _findRelevantNodeData5 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1, add2),
        data = _findRelevantNodeData5[0],
        name = _findRelevantNodeData5[1],
        updater = _findRelevantNodeData5[2];
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError("Graph.".concat(method, ": updater should be a function."));
      var attributes = data.attributes;
      var value = updater(attributes[name]);
      attributes[name] = value;

      // Emitting
      this.emit('nodeAttributesUpdated', {
        key: data.key,
        type: 'set',
        attributes: data.attributes,
        name: name
      });
      return this;
    };
  }
  function attachNodeAttributeRemover(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1) {
      var _findRelevantNodeData6 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1),
        data = _findRelevantNodeData6[0],
        name = _findRelevantNodeData6[1];
      delete data.attributes[name];

      // Emitting
      this.emit('nodeAttributesUpdated', {
        key: data.key,
        type: 'remove',
        attributes: data.attributes,
        name: name
      });
      return this;
    };
  }
  function attachNodeAttributesReplacer(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1) {
      var _findRelevantNodeData7 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1),
        data = _findRelevantNodeData7[0],
        attributes = _findRelevantNodeData7[1];
      if (!isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.".concat(method, ": provided attributes are not a plain object."));
      data.attributes = attributes;

      // Emitting
      this.emit('nodeAttributesUpdated', {
        key: data.key,
        type: 'replace',
        attributes: data.attributes
      });
      return this;
    };
  }
  function attachNodeAttributesMerger(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1) {
      var _findRelevantNodeData8 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1),
        data = _findRelevantNodeData8[0],
        attributes = _findRelevantNodeData8[1];
      if (!isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.".concat(method, ": provided attributes are not a plain object."));
      assign(data.attributes, attributes);

      // Emitting
      this.emit('nodeAttributesUpdated', {
        key: data.key,
        type: 'merge',
        attributes: data.attributes,
        data: attributes
      });
      return this;
    };
  }
  function attachNodeAttributesUpdater(Class, method, mode) {
    Class.prototype[method] = function (nodeOrEdge, nameOrEdge, add1) {
      var _findRelevantNodeData9 = findRelevantNodeData(this, method, mode, nodeOrEdge, nameOrEdge, add1),
        data = _findRelevantNodeData9[0],
        updater = _findRelevantNodeData9[1];
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError("Graph.".concat(method, ": provided updater is not a function."));
      data.attributes = updater(data.attributes);

      // Emitting
      this.emit('nodeAttributesUpdated', {
        key: data.key,
        type: 'update',
        attributes: data.attributes
      });
      return this;
    };
  }

  /**
   * List of methods to attach.
   */
  var NODE_ATTRIBUTES_METHODS = [{
    name: function name(element) {
      return "get".concat(element, "Attribute");
    },
    attacher: attachNodeAttributeGetter
  }, {
    name: function name(element) {
      return "get".concat(element, "Attributes");
    },
    attacher: attachNodeAttributesGetter
  }, {
    name: function name(element) {
      return "has".concat(element, "Attribute");
    },
    attacher: attachNodeAttributeChecker
  }, {
    name: function name(element) {
      return "set".concat(element, "Attribute");
    },
    attacher: attachNodeAttributeSetter
  }, {
    name: function name(element) {
      return "update".concat(element, "Attribute");
    },
    attacher: attachNodeAttributeUpdater
  }, {
    name: function name(element) {
      return "remove".concat(element, "Attribute");
    },
    attacher: attachNodeAttributeRemover
  }, {
    name: function name(element) {
      return "replace".concat(element, "Attributes");
    },
    attacher: attachNodeAttributesReplacer
  }, {
    name: function name(element) {
      return "merge".concat(element, "Attributes");
    },
    attacher: attachNodeAttributesMerger
  }, {
    name: function name(element) {
      return "update".concat(element, "Attributes");
    },
    attacher: attachNodeAttributesUpdater
  }];

  /**
   * Attach every attributes-related methods to a Graph class.
   *
   * @param {function} Graph - Target class.
   */
  function attachNodeAttributesMethods(Graph) {
    NODE_ATTRIBUTES_METHODS.forEach(function (_ref) {
      var name = _ref.name,
        attacher = _ref.attacher;
      // For nodes
      attacher(Graph, name('Node'), NODE);

      // For sources
      attacher(Graph, name('Source'), SOURCE);

      // For targets
      attacher(Graph, name('Target'), TARGET);

      // For opposites
      attacher(Graph, name('Opposite'), OPPOSITE);
    });
  }

  /**
   * Graphology Edge Attributes methods
   * ===================================
   */

  /**
   * Attach an attribute getter method onto the provided class.
   *
   * @param {function} Class         - Target class.
   * @param {string}   method        - Method name.
   * @param {string}   type          - Type of the edge to find.
   */
  function attachEdgeAttributeGetter(Class, method, type) {
    /**
     * Get the desired attribute for the given element (node or edge).
     *
     * Arity 2:
     * @param  {any}    element - Target element.
     * @param  {string} name    - Attribute's name.
     *
     * Arity 3 (only for edges):
     * @param  {any}     source - Source element.
     * @param  {any}     target - Target element.
     * @param  {string}  name   - Attribute's name.
     *
     * @return {mixed}          - The attribute's value.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, name) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 2) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element;
        var target = '' + name;
        name = arguments[2];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      return data.attributes[name];
    };
  }

  /**
   * Attach an attributes getter method onto the provided class.
   *
   * @param {function} Class       - Target class.
   * @param {string}   method      - Method name.
   * @param {string}   type        - Type of the edge to find.
   */
  function attachEdgeAttributesGetter(Class, method, type) {
    /**
     * Retrieves all the target element's attributes.
     *
     * Arity 2:
     * @param  {any}    element - Target element.
     *
     * Arity 3 (only for edges):
     * @param  {any}     source - Source element.
     * @param  {any}     target - Target element.
     *
     * @return {object}          - The element's attributes.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 1) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element,
          target = '' + arguments[1];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      return data.attributes;
    };
  }

  /**
   * Attach an attribute checker method onto the provided class.
   *
   * @param {function} Class       - Target class.
   * @param {string}   method      - Method name.
   * @param {string}   type        - Type of the edge to find.
   */
  function attachEdgeAttributeChecker(Class, method, type) {
    /**
     * Checks whether the desired attribute is set for the given element (node or edge).
     *
     * Arity 2:
     * @param  {any}    element - Target element.
     * @param  {string} name    - Attribute's name.
     *
     * Arity 3 (only for edges):
     * @param  {any}     source - Source element.
     * @param  {any}     target - Target element.
     * @param  {string}  name   - Attribute's name.
     *
     * @return {boolean}
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, name) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 2) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element;
        var target = '' + name;
        name = arguments[2];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      return data.attributes.hasOwnProperty(name);
    };
  }

  /**
   * Attach an attribute setter method onto the provided class.
   *
   * @param {function} Class         - Target class.
   * @param {string}   method        - Method name.
   * @param {string}   type          - Type of the edge to find.
   */
  function attachEdgeAttributeSetter(Class, method, type) {
    /**
     * Set the desired attribute for the given element (node or edge).
     *
     * Arity 2:
     * @param  {any}    element - Target element.
     * @param  {string} name    - Attribute's name.
     * @param  {mixed}  value   - New attribute value.
     *
     * Arity 3 (only for edges):
     * @param  {any}     source - Source element.
     * @param  {any}     target - Target element.
     * @param  {string}  name   - Attribute's name.
     * @param  {mixed}  value   - New attribute value.
     *
     * @return {Graph}          - Returns itself for chaining.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, name, value) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 3) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element;
        var target = '' + name;
        name = arguments[2];
        value = arguments[3];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      data.attributes[name] = value;

      // Emitting
      this.emit('edgeAttributesUpdated', {
        key: data.key,
        type: 'set',
        attributes: data.attributes,
        name: name
      });
      return this;
    };
  }

  /**
   * Attach an attribute updater method onto the provided class.
   *
   * @param {function} Class         - Target class.
   * @param {string}   method        - Method name.
   * @param {string}   type          - Type of the edge to find.
   */
  function attachEdgeAttributeUpdater(Class, method, type) {
    /**
     * Update the desired attribute for the given element (node or edge) using
     * the provided function.
     *
     * Arity 2:
     * @param  {any}      element - Target element.
     * @param  {string}   name    - Attribute's name.
     * @param  {function} updater - Updater function.
     *
     * Arity 3 (only for edges):
     * @param  {any}      source  - Source element.
     * @param  {any}      target  - Target element.
     * @param  {string}   name    - Attribute's name.
     * @param  {function} updater - Updater function.
     *
     * @return {Graph}            - Returns itself for chaining.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, name, updater) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 3) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element;
        var target = '' + name;
        name = arguments[2];
        updater = arguments[3];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError("Graph.".concat(method, ": updater should be a function."));
      data.attributes[name] = updater(data.attributes[name]);

      // Emitting
      this.emit('edgeAttributesUpdated', {
        key: data.key,
        type: 'set',
        attributes: data.attributes,
        name: name
      });
      return this;
    };
  }

  /**
   * Attach an attribute remover method onto the provided class.
   *
   * @param {function} Class         - Target class.
   * @param {string}   method        - Method name.
   * @param {string}   type          - Type of the edge to find.
   */
  function attachEdgeAttributeRemover(Class, method, type) {
    /**
     * Remove the desired attribute for the given element (node or edge).
     *
     * Arity 2:
     * @param  {any}    element - Target element.
     * @param  {string} name    - Attribute's name.
     *
     * Arity 3 (only for edges):
     * @param  {any}     source - Source element.
     * @param  {any}     target - Target element.
     * @param  {string}  name   - Attribute's name.
     *
     * @return {Graph}          - Returns itself for chaining.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, name) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 2) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element;
        var target = '' + name;
        name = arguments[2];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      delete data.attributes[name];

      // Emitting
      this.emit('edgeAttributesUpdated', {
        key: data.key,
        type: 'remove',
        attributes: data.attributes,
        name: name
      });
      return this;
    };
  }

  /**
   * Attach an attribute replacer method onto the provided class.
   *
   * @param {function} Class         - Target class.
   * @param {string}   method        - Method name.
   * @param {string}   type          - Type of the edge to find.
   */
  function attachEdgeAttributesReplacer(Class, method, type) {
    /**
     * Replace the attributes for the given element (node or edge).
     *
     * Arity 2:
     * @param  {any}    element    - Target element.
     * @param  {object} attributes - New attributes.
     *
     * Arity 3 (only for edges):
     * @param  {any}     source     - Source element.
     * @param  {any}     target     - Target element.
     * @param  {object}  attributes - New attributes.
     *
     * @return {Graph}              - Returns itself for chaining.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, attributes) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 2) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element,
          target = '' + attributes;
        attributes = arguments[2];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      if (!isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.".concat(method, ": provided attributes are not a plain object."));
      data.attributes = attributes;

      // Emitting
      this.emit('edgeAttributesUpdated', {
        key: data.key,
        type: 'replace',
        attributes: data.attributes
      });
      return this;
    };
  }

  /**
   * Attach an attribute merger method onto the provided class.
   *
   * @param {function} Class         - Target class.
   * @param {string}   method        - Method name.
   * @param {string}   type          - Type of the edge to find.
   */
  function attachEdgeAttributesMerger(Class, method, type) {
    /**
     * Merge the attributes for the given element (node or edge).
     *
     * Arity 2:
     * @param  {any}    element    - Target element.
     * @param  {object} attributes - Attributes to merge.
     *
     * Arity 3 (only for edges):
     * @param  {any}     source     - Source element.
     * @param  {any}     target     - Target element.
     * @param  {object}  attributes - Attributes to merge.
     *
     * @return {Graph}              - Returns itself for chaining.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, attributes) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 2) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element,
          target = '' + attributes;
        attributes = arguments[2];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      if (!isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.".concat(method, ": provided attributes are not a plain object."));
      assign(data.attributes, attributes);

      // Emitting
      this.emit('edgeAttributesUpdated', {
        key: data.key,
        type: 'merge',
        attributes: data.attributes,
        data: attributes
      });
      return this;
    };
  }

  /**
   * Attach an attribute updater method onto the provided class.
   *
   * @param {function} Class         - Target class.
   * @param {string}   method        - Method name.
   * @param {string}   type          - Type of the edge to find.
   */
  function attachEdgeAttributesUpdater(Class, method, type) {
    /**
     * Update the attributes of the given element (node or edge).
     *
     * Arity 2:
     * @param  {any}      element - Target element.
     * @param  {function} updater - Updater function.
     *
     * Arity 3 (only for edges):
     * @param  {any}      source  - Source element.
     * @param  {any}      target  - Target element.
     * @param  {function} updater - Updater function.
     *
     * @return {Graph}            - Returns itself for chaining.
     *
     * @throws {Error} - Will throw if too many arguments are provided.
     * @throws {Error} - Will throw if any of the elements is not found.
     */
    Class.prototype[method] = function (element, updater) {
      var data;
      if (this.type !== 'mixed' && type !== 'mixed' && type !== this.type) throw new UsageGraphError("Graph.".concat(method, ": cannot find this type of edges in your ").concat(this.type, " graph."));
      if (arguments.length > 2) {
        if (this.multi) throw new UsageGraphError("Graph.".concat(method, ": cannot use a {source,target} combo when asking about an edge's attributes in a MultiGraph since we cannot infer the one you want information about."));
        var source = '' + element,
          target = '' + updater;
        updater = arguments[2];
        data = getMatchingEdge(this, source, target, type);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find an edge for the given path (\"").concat(source, "\" - \"").concat(target, "\")."));
      } else {
        if (type !== 'mixed') throw new UsageGraphError("Graph.".concat(method, ": calling this method with only a key (vs. a source and target) does not make sense since an edge with this key could have the other type."));
        element = '' + element;
        data = this._edges.get(element);
        if (!data) throw new NotFoundGraphError("Graph.".concat(method, ": could not find the \"").concat(element, "\" edge in the graph."));
      }
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError("Graph.".concat(method, ": provided updater is not a function."));
      data.attributes = updater(data.attributes);

      // Emitting
      this.emit('edgeAttributesUpdated', {
        key: data.key,
        type: 'update',
        attributes: data.attributes
      });
      return this;
    };
  }

  /**
   * List of methods to attach.
   */
  var EDGE_ATTRIBUTES_METHODS = [{
    name: function name(element) {
      return "get".concat(element, "Attribute");
    },
    attacher: attachEdgeAttributeGetter
  }, {
    name: function name(element) {
      return "get".concat(element, "Attributes");
    },
    attacher: attachEdgeAttributesGetter
  }, {
    name: function name(element) {
      return "has".concat(element, "Attribute");
    },
    attacher: attachEdgeAttributeChecker
  }, {
    name: function name(element) {
      return "set".concat(element, "Attribute");
    },
    attacher: attachEdgeAttributeSetter
  }, {
    name: function name(element) {
      return "update".concat(element, "Attribute");
    },
    attacher: attachEdgeAttributeUpdater
  }, {
    name: function name(element) {
      return "remove".concat(element, "Attribute");
    },
    attacher: attachEdgeAttributeRemover
  }, {
    name: function name(element) {
      return "replace".concat(element, "Attributes");
    },
    attacher: attachEdgeAttributesReplacer
  }, {
    name: function name(element) {
      return "merge".concat(element, "Attributes");
    },
    attacher: attachEdgeAttributesMerger
  }, {
    name: function name(element) {
      return "update".concat(element, "Attributes");
    },
    attacher: attachEdgeAttributesUpdater
  }];

  /**
   * Attach every attributes-related methods to a Graph class.
   *
   * @param {function} Graph - Target class.
   */
  function attachEdgeAttributesMethods(Graph) {
    EDGE_ATTRIBUTES_METHODS.forEach(function (_ref) {
      var name = _ref.name,
        attacher = _ref.attacher;
      // For edges
      attacher(Graph, name('Edge'), 'mixed');

      // For directed edges
      attacher(Graph, name('DirectedEdge'), 'directed');

      // For undirected edges
      attacher(Graph, name('UndirectedEdge'), 'undirected');
    });
  }

  /**
   * Definitions.
   */
  var EDGES_ITERATION = [{
    name: 'edges',
    type: 'mixed'
  }, {
    name: 'inEdges',
    type: 'directed',
    direction: 'in'
  }, {
    name: 'outEdges',
    type: 'directed',
    direction: 'out'
  }, {
    name: 'inboundEdges',
    type: 'mixed',
    direction: 'in'
  }, {
    name: 'outboundEdges',
    type: 'mixed',
    direction: 'out'
  }, {
    name: 'directedEdges',
    type: 'directed'
  }, {
    name: 'undirectedEdges',
    type: 'undirected'
  }];

  /**
   * Function iterating over edges from the given object to match one of them.
   *
   * @param {object}   object   - Target object.
   * @param {function} callback - Function to call.
   */
  function forEachSimple(breakable, object, callback, avoid) {
    var shouldBreak = false;
    for (var k in object) {
      if (k === avoid) continue;
      var edgeData = object[k];
      shouldBreak = callback(edgeData.key, edgeData.attributes, edgeData.source.key, edgeData.target.key, edgeData.source.attributes, edgeData.target.attributes, edgeData.undirected);
      if (breakable && shouldBreak) return edgeData.key;
    }
    return;
  }
  function forEachMulti(breakable, object, callback, avoid) {
    var edgeData, source, target;
    var shouldBreak = false;
    for (var k in object) {
      if (k === avoid) continue;
      edgeData = object[k];
      do {
        source = edgeData.source;
        target = edgeData.target;
        shouldBreak = callback(edgeData.key, edgeData.attributes, source.key, target.key, source.attributes, target.attributes, edgeData.undirected);
        if (breakable && shouldBreak) return edgeData.key;
        edgeData = edgeData.next;
      } while (edgeData !== undefined);
    }
    return;
  }

  /**
   * Function returning an iterator over edges from the given object.
   *
   * @param  {object}   object - Target object.
   * @return {Iterator}
   */
  function createIterator(object, avoid) {
    var keys = Object.keys(object);
    var l = keys.length;
    var edgeData;
    var i = 0;
    return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
      return this;
    }), "next", function next() {
      do {
        if (!edgeData) {
          if (i >= l) return {
            done: true
          };
          var k = keys[i++];
          if (k === avoid) {
            edgeData = undefined;
            continue;
          }
          edgeData = object[k];
        } else {
          edgeData = edgeData.next;
        }
      } while (!edgeData);
      return {
        done: false,
        value: {
          edge: edgeData.key,
          attributes: edgeData.attributes,
          source: edgeData.source.key,
          target: edgeData.target.key,
          sourceAttributes: edgeData.source.attributes,
          targetAttributes: edgeData.target.attributes,
          undirected: edgeData.undirected
        }
      };
    });
  }

  /**
   * Function iterating over the egdes from the object at given key to match
   * one of them.
   *
   * @param {object}   object   - Target object.
   * @param {mixed}    k        - Neighbor key.
   * @param {function} callback - Callback to use.
   */
  function forEachForKeySimple(breakable, object, k, callback) {
    var edgeData = object[k];
    if (!edgeData) return;
    var sourceData = edgeData.source;
    var targetData = edgeData.target;
    if (callback(edgeData.key, edgeData.attributes, sourceData.key, targetData.key, sourceData.attributes, targetData.attributes, edgeData.undirected) && breakable) return edgeData.key;
  }
  function forEachForKeyMulti(breakable, object, k, callback) {
    var edgeData = object[k];
    if (!edgeData) return;
    var shouldBreak = false;
    do {
      shouldBreak = callback(edgeData.key, edgeData.attributes, edgeData.source.key, edgeData.target.key, edgeData.source.attributes, edgeData.target.attributes, edgeData.undirected);
      if (breakable && shouldBreak) return edgeData.key;
      edgeData = edgeData.next;
    } while (edgeData !== undefined);
    return;
  }

  /**
   * Function returning an iterator over the egdes from the object at given key.
   *
   * @param  {object}   object   - Target object.
   * @param  {mixed}    k        - Neighbor key.
   * @return {Iterator}
   */
  function createIteratorForKey(object, k) {
    var edgeData = object[k];
    if (edgeData.next !== undefined) {
      return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
        return this;
      }), "next", function next() {
        if (!edgeData) return {
          done: true
        };
        var value = {
          edge: edgeData.key,
          attributes: edgeData.attributes,
          source: edgeData.source.key,
          target: edgeData.target.key,
          sourceAttributes: edgeData.source.attributes,
          targetAttributes: edgeData.target.attributes,
          undirected: edgeData.undirected
        };
        edgeData = edgeData.next;
        return {
          done: false,
          value: value
        };
      });
    }
    var done = false;
    return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
      return this;
    }), "next", function next() {
      if (done === true) return {
        done: true
      };
      done = true;
      return {
        done: false,
        value: {
          edge: edgeData.key,
          attributes: edgeData.attributes,
          source: edgeData.source.key,
          target: edgeData.target.key,
          sourceAttributes: edgeData.source.attributes,
          targetAttributes: edgeData.target.attributes,
          undirected: edgeData.undirected
        }
      };
    });
  }

  /**
   * Function creating an array of edges for the given type.
   *
   * @param  {Graph}   graph - Target Graph instance.
   * @param  {string}  type  - Type of edges to retrieve.
   * @return {array}         - Array of edges.
   */
  function createEdgeArray(graph, type) {
    if (graph.size === 0) return [];
    if (type === 'mixed' || type === graph.type) {
      return Array.from(graph._edges.keys());
    }
    var size = type === 'undirected' ? graph.undirectedSize : graph.directedSize;
    var list = new Array(size),
      mask = type === 'undirected';
    var iterator = graph._edges.values();
    var i = 0;
    var step, data;
    while (step = iterator.next(), step.done !== true) {
      data = step.value;
      if (data.undirected === mask) list[i++] = data.key;
    }
    return list;
  }

  /**
   * Function iterating over a graph's edges using a callback to match one of
   * them.
   *
   * @param  {Graph}    graph    - Target Graph instance.
   * @param  {string}   type     - Type of edges to retrieve.
   * @param  {function} callback - Function to call.
   */
  function forEachEdge(breakable, graph, type, callback) {
    if (graph.size === 0) return;
    var shouldFilter = type !== 'mixed' && type !== graph.type;
    var mask = type === 'undirected';
    var step, data;
    var shouldBreak = false;
    var iterator = graph._edges.values();
    while (step = iterator.next(), step.done !== true) {
      data = step.value;
      if (shouldFilter && data.undirected !== mask) continue;
      var _data = data,
        key = _data.key,
        attributes = _data.attributes,
        source = _data.source,
        target = _data.target;
      shouldBreak = callback(key, attributes, source.key, target.key, source.attributes, target.attributes, data.undirected);
      if (breakable && shouldBreak) return key;
    }
    return;
  }

  /**
   * Function creating an iterator of edges for the given type.
   *
   * @param  {Graph}    graph - Target Graph instance.
   * @param  {string}   type  - Type of edges to retrieve.
   * @return {Iterator}
   */
  function createEdgeIterator(graph, type) {
    if (graph.size === 0) return emptyIterator();
    var shouldFilter = type !== 'mixed' && type !== graph.type;
    var mask = type === 'undirected';
    var iterator = graph._edges.values();
    return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
      return this;
    }), "next", function next() {
      var step, data;

      // eslint-disable-next-line no-constant-condition
      while (true) {
        step = iterator.next();
        if (step.done) return step;
        data = step.value;
        if (shouldFilter && data.undirected !== mask) continue;
        break;
      }
      var value = {
        edge: data.key,
        attributes: data.attributes,
        source: data.source.key,
        target: data.target.key,
        sourceAttributes: data.source.attributes,
        targetAttributes: data.target.attributes,
        undirected: data.undirected
      };
      return {
        value: value,
        done: false
      };
    });
  }

  /**
   * Function iterating over a node's edges using a callback to match one of them.
   *
   * @param  {boolean}  multi     - Whether the graph is multi or not.
   * @param  {string}   type      - Type of edges to retrieve.
   * @param  {string}   direction - In or out?
   * @param  {any}      nodeData  - Target node's data.
   * @param  {function} callback  - Function to call.
   */
  function forEachEdgeForNode(breakable, multi, type, direction, nodeData, callback) {
    var fn = multi ? forEachMulti : forEachSimple;
    var found;
    if (type !== 'undirected') {
      if (direction !== 'out') {
        found = fn(breakable, nodeData["in"], callback);
        if (breakable && found) return found;
      }
      if (direction !== 'in') {
        found = fn(breakable, nodeData.out, callback, !direction ? nodeData.key : undefined);
        if (breakable && found) return found;
      }
    }
    if (type !== 'directed') {
      found = fn(breakable, nodeData.undirected, callback);
      if (breakable && found) return found;
    }
    return;
  }

  /**
   * Function creating an array of edges for the given type & the given node.
   *
   * @param  {boolean} multi     - Whether the graph is multi or not.
   * @param  {string}  type      - Type of edges to retrieve.
   * @param  {string}  direction - In or out?
   * @param  {any}     nodeData  - Target node's data.
   * @return {array}             - Array of edges.
   */
  function createEdgeArrayForNode(multi, type, direction, nodeData) {
    var edges = []; // TODO: possibility to know size beforehand or factorize with map

    forEachEdgeForNode(false, multi, type, direction, nodeData, function (key) {
      edges.push(key);
    });
    return edges;
  }

  /**
   * Function iterating over a node's edges using a callback.
   *
   * @param  {string}   type      - Type of edges to retrieve.
   * @param  {string}   direction - In or out?
   * @param  {any}      nodeData  - Target node's data.
   * @return {Iterator}
   */
  function createEdgeIteratorForNode(type, direction, nodeData) {
    var iterator = emptyIterator();
    if (type !== 'undirected') {
      if (direction !== 'out' && typeof nodeData["in"] !== 'undefined') iterator = chain(iterator, createIterator(nodeData["in"]));
      if (direction !== 'in' && typeof nodeData.out !== 'undefined') iterator = chain(iterator, createIterator(nodeData.out, !direction ? nodeData.key : undefined));
    }
    if (type !== 'directed' && typeof nodeData.undirected !== 'undefined') {
      iterator = chain(iterator, createIterator(nodeData.undirected));
    }
    return iterator;
  }

  /**
   * Function iterating over edges for the given path using a callback to match
   * one of them.
   *
   * @param  {string}   type       - Type of edges to retrieve.
   * @param  {boolean}  multi      - Whether the graph is multi.
   * @param  {string}   direction  - In or out?
   * @param  {NodeData} sourceData - Source node's data.
   * @param  {string}   target     - Target node.
   * @param  {function} callback   - Function to call.
   */
  function forEachEdgeForPath(breakable, type, multi, direction, sourceData, target, callback) {
    var fn = multi ? forEachForKeyMulti : forEachForKeySimple;
    var found;
    if (type !== 'undirected') {
      if (typeof sourceData["in"] !== 'undefined' && direction !== 'out') {
        found = fn(breakable, sourceData["in"], target, callback);
        if (breakable && found) return found;
      }
      if (typeof sourceData.out !== 'undefined' && direction !== 'in' && (direction || sourceData.key !== target)) {
        found = fn(breakable, sourceData.out, target, callback);
        if (breakable && found) return found;
      }
    }
    if (type !== 'directed') {
      if (typeof sourceData.undirected !== 'undefined') {
        found = fn(breakable, sourceData.undirected, target, callback);
        if (breakable && found) return found;
      }
    }
    return;
  }

  /**
   * Function creating an array of edges for the given path.
   *
   * @param  {string}   type       - Type of edges to retrieve.
   * @param  {boolean}  multi      - Whether the graph is multi.
   * @param  {string}   direction  - In or out?
   * @param  {NodeData} sourceData - Source node's data.
   * @param  {any}      target     - Target node.
   * @return {array}               - Array of edges.
   */
  function createEdgeArrayForPath(type, multi, direction, sourceData, target) {
    var edges = []; // TODO: possibility to know size beforehand or factorize with map

    forEachEdgeForPath(false, type, multi, direction, sourceData, target, function (key) {
      edges.push(key);
    });
    return edges;
  }

  /**
   * Function returning an iterator over edges for the given path.
   *
   * @param  {string}   type       - Type of edges to retrieve.
   * @param  {string}   direction  - In or out?
   * @param  {NodeData} sourceData - Source node's data.
   * @param  {string}   target     - Target node.
   * @param  {function} callback   - Function to call.
   */
  function createEdgeIteratorForPath(type, direction, sourceData, target) {
    var iterator = emptyIterator();
    if (type !== 'undirected') {
      if (typeof sourceData["in"] !== 'undefined' && direction !== 'out' && target in sourceData["in"]) iterator = chain(iterator, createIteratorForKey(sourceData["in"], target));
      if (typeof sourceData.out !== 'undefined' && direction !== 'in' && target in sourceData.out && (direction || sourceData.key !== target)) iterator = chain(iterator, createIteratorForKey(sourceData.out, target));
    }
    if (type !== 'directed') {
      if (typeof sourceData.undirected !== 'undefined' && target in sourceData.undirected) iterator = chain(iterator, createIteratorForKey(sourceData.undirected, target));
    }
    return iterator;
  }

  /**
   * Function attaching an edge array creator method to the Graph prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachEdgeArrayCreator(Class, description) {
    var name = description.name,
      type = description.type,
      direction = description.direction;

    /**
     * Function returning an array of certain edges.
     *
     * Arity 0: Return all the relevant edges.
     *
     * Arity 1: Return all of a node's relevant edges.
     * @param  {any}   node   - Target node.
     *
     * Arity 2: Return the relevant edges across the given path.
     * @param  {any}   source - Source node.
     * @param  {any}   target - Target node.
     *
     * @return {array|number} - The edges or the number of edges.
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    Class.prototype[name] = function (source, target) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return [];
      if (!arguments.length) return createEdgeArray(this, type);
      if (arguments.length === 1) {
        source = '' + source;
        var nodeData = this._nodes.get(source);
        if (typeof nodeData === 'undefined') throw new NotFoundGraphError("Graph.".concat(name, ": could not find the \"").concat(source, "\" node in the graph."));

        // Iterating over a node's edges
        return createEdgeArrayForNode(this.multi, type === 'mixed' ? this.type : type, direction, nodeData);
      }
      if (arguments.length === 2) {
        source = '' + source;
        target = '' + target;
        var sourceData = this._nodes.get(source);
        if (!sourceData) throw new NotFoundGraphError("Graph.".concat(name, ":  could not find the \"").concat(source, "\" source node in the graph."));
        if (!this._nodes.has(target)) throw new NotFoundGraphError("Graph.".concat(name, ":  could not find the \"").concat(target, "\" target node in the graph."));

        // Iterating over the edges between source & target
        return createEdgeArrayForPath(type, this.multi, direction, sourceData, target);
      }
      throw new InvalidArgumentsGraphError("Graph.".concat(name, ": too many arguments (expecting 0, 1 or 2 and got ").concat(arguments.length, ")."));
    };
  }

  /**
   * Function attaching a edge callback iterator method to the Graph prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachForEachEdge(Class, description) {
    var name = description.name,
      type = description.type,
      direction = description.direction;
    var forEachName = 'forEach' + name[0].toUpperCase() + name.slice(1, -1);

    /**
     * Function iterating over the graph's relevant edges by applying the given
     * callback.
     *
     * Arity 1: Iterate over all the relevant edges.
     * @param  {function} callback - Callback to use.
     *
     * Arity 2: Iterate over all of a node's relevant edges.
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * Arity 3: Iterate over the relevant edges across the given path.
     * @param  {any}      source   - Source node.
     * @param  {any}      target   - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    Class.prototype[forEachName] = function (source, target, callback) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return;
      if (arguments.length === 1) {
        callback = source;
        return forEachEdge(false, this, type, callback);
      }
      if (arguments.length === 2) {
        source = '' + source;
        callback = target;
        var nodeData = this._nodes.get(source);
        if (typeof nodeData === 'undefined') throw new NotFoundGraphError("Graph.".concat(forEachName, ": could not find the \"").concat(source, "\" node in the graph."));

        // Iterating over a node's edges
        // TODO: maybe attach the sub method to the instance dynamically?
        return forEachEdgeForNode(false, this.multi, type === 'mixed' ? this.type : type, direction, nodeData, callback);
      }
      if (arguments.length === 3) {
        source = '' + source;
        target = '' + target;
        var sourceData = this._nodes.get(source);
        if (!sourceData) throw new NotFoundGraphError("Graph.".concat(forEachName, ":  could not find the \"").concat(source, "\" source node in the graph."));
        if (!this._nodes.has(target)) throw new NotFoundGraphError("Graph.".concat(forEachName, ":  could not find the \"").concat(target, "\" target node in the graph."));

        // Iterating over the edges between source & target
        return forEachEdgeForPath(false, type, this.multi, direction, sourceData, target, callback);
      }
      throw new InvalidArgumentsGraphError("Graph.".concat(forEachName, ": too many arguments (expecting 1, 2 or 3 and got ").concat(arguments.length, ")."));
    };

    /**
     * Function mapping the graph's relevant edges by applying the given
     * callback.
     *
     * Arity 1: Map all the relevant edges.
     * @param  {function} callback - Callback to use.
     *
     * Arity 2: Map all of a node's relevant edges.
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * Arity 3: Map the relevant edges across the given path.
     * @param  {any}      source   - Source node.
     * @param  {any}      target   - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var mapName = 'map' + name[0].toUpperCase() + name.slice(1);
    Class.prototype[mapName] = function () {
      var args = Array.prototype.slice.call(arguments);
      var callback = args.pop();
      var result;

      // We know the result length beforehand
      if (args.length === 0) {
        var length = 0;
        if (type !== 'directed') length += this.undirectedSize;
        if (type !== 'undirected') length += this.directedSize;
        result = new Array(length);
        var i = 0;
        args.push(function (e, ea, s, t, sa, ta, u) {
          result[i++] = callback(e, ea, s, t, sa, ta, u);
        });
      }

      // We don't know the result length beforehand
      // TODO: we can in some instances of simple graphs, knowing degree
      else {
        result = [];
        args.push(function (e, ea, s, t, sa, ta, u) {
          result.push(callback(e, ea, s, t, sa, ta, u));
        });
      }
      this[forEachName].apply(this, args);
      return result;
    };

    /**
     * Function filtering the graph's relevant edges using the provided predicate
     * function.
     *
     * Arity 1: Filter all the relevant edges.
     * @param  {function} predicate - Predicate to use.
     *
     * Arity 2: Filter all of a node's relevant edges.
     * @param  {any}      node      - Target node.
     * @param  {function} predicate - Predicate to use.
     *
     * Arity 3: Filter the relevant edges across the given path.
     * @param  {any}      source    - Source node.
     * @param  {any}      target    - Target node.
     * @param  {function} predicate - Predicate to use.
     *
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var filterName = 'filter' + name[0].toUpperCase() + name.slice(1);
    Class.prototype[filterName] = function () {
      var args = Array.prototype.slice.call(arguments);
      var callback = args.pop();
      var result = [];
      args.push(function (e, ea, s, t, sa, ta, u) {
        if (callback(e, ea, s, t, sa, ta, u)) result.push(e);
      });
      this[forEachName].apply(this, args);
      return result;
    };

    /**
     * Function reducing the graph's relevant edges using the provided accumulator
     * function.
     *
     * Arity 1: Reduce all the relevant edges.
     * @param  {function} accumulator  - Accumulator to use.
     * @param  {any}      initialValue - Initial value.
     *
     * Arity 2: Reduce all of a node's relevant edges.
     * @param  {any}      node         - Target node.
     * @param  {function} accumulator  - Accumulator to use.
     * @param  {any}      initialValue - Initial value.
     *
     * Arity 3: Reduce the relevant edges across the given path.
     * @param  {any}      source       - Source node.
     * @param  {any}      target       - Target node.
     * @param  {function} accumulator  - Accumulator to use.
     * @param  {any}      initialValue - Initial value.
     *
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var reduceName = 'reduce' + name[0].toUpperCase() + name.slice(1);
    Class.prototype[reduceName] = function () {
      var args = Array.prototype.slice.call(arguments);
      if (args.length < 2 || args.length > 4) {
        throw new InvalidArgumentsGraphError("Graph.".concat(reduceName, ": invalid number of arguments (expecting 2, 3 or 4 and got ").concat(args.length, ")."));
      }
      if (typeof args[args.length - 1] === 'function' && typeof args[args.length - 2] !== 'function') {
        throw new InvalidArgumentsGraphError("Graph.".concat(reduceName, ": missing initial value. You must provide it because the callback takes more than one argument and we cannot infer the initial value from the first iteration, as you could with a simple array."));
      }
      var callback;
      var initialValue;
      if (args.length === 2) {
        callback = args[0];
        initialValue = args[1];
        args = [];
      } else if (args.length === 3) {
        callback = args[1];
        initialValue = args[2];
        args = [args[0]];
      } else if (args.length === 4) {
        callback = args[2];
        initialValue = args[3];
        args = [args[0], args[1]];
      }
      var accumulator = initialValue;
      args.push(function (e, ea, s, t, sa, ta, u) {
        accumulator = callback(accumulator, e, ea, s, t, sa, ta, u);
      });
      this[forEachName].apply(this, args);
      return accumulator;
    };
  }

  /**
   * Function attaching a breakable edge callback iterator method to the Graph
   * prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachFindEdge(Class, description) {
    var name = description.name,
      type = description.type,
      direction = description.direction;
    var findEdgeName = 'find' + name[0].toUpperCase() + name.slice(1, -1);

    /**
     * Function iterating over the graph's relevant edges in order to match
     * one of them using the provided predicate function.
     *
     * Arity 1: Iterate over all the relevant edges.
     * @param  {function} callback - Callback to use.
     *
     * Arity 2: Iterate over all of a node's relevant edges.
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * Arity 3: Iterate over the relevant edges across the given path.
     * @param  {any}      source   - Source node.
     * @param  {any}      target   - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    Class.prototype[findEdgeName] = function (source, target, callback) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return false;
      if (arguments.length === 1) {
        callback = source;
        return forEachEdge(true, this, type, callback);
      }
      if (arguments.length === 2) {
        source = '' + source;
        callback = target;
        var nodeData = this._nodes.get(source);
        if (typeof nodeData === 'undefined') throw new NotFoundGraphError("Graph.".concat(findEdgeName, ": could not find the \"").concat(source, "\" node in the graph."));

        // Iterating over a node's edges
        // TODO: maybe attach the sub method to the instance dynamically?
        return forEachEdgeForNode(true, this.multi, type === 'mixed' ? this.type : type, direction, nodeData, callback);
      }
      if (arguments.length === 3) {
        source = '' + source;
        target = '' + target;
        var sourceData = this._nodes.get(source);
        if (!sourceData) throw new NotFoundGraphError("Graph.".concat(findEdgeName, ":  could not find the \"").concat(source, "\" source node in the graph."));
        if (!this._nodes.has(target)) throw new NotFoundGraphError("Graph.".concat(findEdgeName, ":  could not find the \"").concat(target, "\" target node in the graph."));

        // Iterating over the edges between source & target
        return forEachEdgeForPath(true, type, this.multi, direction, sourceData, target, callback);
      }
      throw new InvalidArgumentsGraphError("Graph.".concat(findEdgeName, ": too many arguments (expecting 1, 2 or 3 and got ").concat(arguments.length, ")."));
    };

    /**
     * Function iterating over the graph's relevant edges in order to assert
     * whether any one of them matches the provided predicate function.
     *
     * Arity 1: Iterate over all the relevant edges.
     * @param  {function} callback - Callback to use.
     *
     * Arity 2: Iterate over all of a node's relevant edges.
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * Arity 3: Iterate over the relevant edges across the given path.
     * @param  {any}      source   - Source node.
     * @param  {any}      target   - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var someName = 'some' + name[0].toUpperCase() + name.slice(1, -1);
    Class.prototype[someName] = function () {
      var args = Array.prototype.slice.call(arguments);
      var callback = args.pop();
      args.push(function (e, ea, s, t, sa, ta, u) {
        return callback(e, ea, s, t, sa, ta, u);
      });
      var found = this[findEdgeName].apply(this, args);
      if (found) return true;
      return false;
    };

    /**
     * Function iterating over the graph's relevant edges in order to assert
     * whether all of them matche the provided predicate function.
     *
     * Arity 1: Iterate over all the relevant edges.
     * @param  {function} callback - Callback to use.
     *
     * Arity 2: Iterate over all of a node's relevant edges.
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * Arity 3: Iterate over the relevant edges across the given path.
     * @param  {any}      source   - Source node.
     * @param  {any}      target   - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var everyName = 'every' + name[0].toUpperCase() + name.slice(1, -1);
    Class.prototype[everyName] = function () {
      var args = Array.prototype.slice.call(arguments);
      var callback = args.pop();
      args.push(function (e, ea, s, t, sa, ta, u) {
        return !callback(e, ea, s, t, sa, ta, u);
      });
      var found = this[findEdgeName].apply(this, args);
      if (found) return false;
      return true;
    };
  }

  /**
   * Function attaching an edge iterator method to the Graph prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachEdgeIteratorCreator(Class, description) {
    var originalName = description.name,
      type = description.type,
      direction = description.direction;
    var name = originalName.slice(0, -1) + 'Entries';

    /**
     * Function returning an iterator over the graph's edges.
     *
     * Arity 0: Iterate over all the relevant edges.
     *
     * Arity 1: Iterate over all of a node's relevant edges.
     * @param  {any}   node   - Target node.
     *
     * Arity 2: Iterate over the relevant edges across the given path.
     * @param  {any}   source - Source node.
     * @param  {any}   target - Target node.
     *
     * @return {array|number} - The edges or the number of edges.
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    Class.prototype[name] = function (source, target) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return emptyIterator();
      if (!arguments.length) return createEdgeIterator(this, type);
      if (arguments.length === 1) {
        source = '' + source;
        var sourceData = this._nodes.get(source);
        if (!sourceData) throw new NotFoundGraphError("Graph.".concat(name, ": could not find the \"").concat(source, "\" node in the graph."));

        // Iterating over a node's edges
        return createEdgeIteratorForNode(type, direction, sourceData);
      }
      if (arguments.length === 2) {
        source = '' + source;
        target = '' + target;
        var _sourceData = this._nodes.get(source);
        if (!_sourceData) throw new NotFoundGraphError("Graph.".concat(name, ":  could not find the \"").concat(source, "\" source node in the graph."));
        if (!this._nodes.has(target)) throw new NotFoundGraphError("Graph.".concat(name, ":  could not find the \"").concat(target, "\" target node in the graph."));

        // Iterating over the edges between source & target
        return createEdgeIteratorForPath(type, direction, _sourceData, target);
      }
      throw new InvalidArgumentsGraphError("Graph.".concat(name, ": too many arguments (expecting 0, 1 or 2 and got ").concat(arguments.length, ")."));
    };
  }

  /**
   * Function attaching every edge iteration method to the Graph class.
   *
   * @param {function} Graph - Graph class.
   */
  function attachEdgeIterationMethods(Graph) {
    EDGES_ITERATION.forEach(function (description) {
      attachEdgeArrayCreator(Graph, description);
      attachForEachEdge(Graph, description);
      attachFindEdge(Graph, description);
      attachEdgeIteratorCreator(Graph, description);
    });
  }

  /**
   * Definitions.
   */
  var NEIGHBORS_ITERATION = [{
    name: 'neighbors',
    type: 'mixed'
  }, {
    name: 'inNeighbors',
    type: 'directed',
    direction: 'in'
  }, {
    name: 'outNeighbors',
    type: 'directed',
    direction: 'out'
  }, {
    name: 'inboundNeighbors',
    type: 'mixed',
    direction: 'in'
  }, {
    name: 'outboundNeighbors',
    type: 'mixed',
    direction: 'out'
  }, {
    name: 'directedNeighbors',
    type: 'directed'
  }, {
    name: 'undirectedNeighbors',
    type: 'undirected'
  }];

  /**
   * Helpers.
   */
  function CompositeSetWrapper() {
    this.A = null;
    this.B = null;
  }
  CompositeSetWrapper.prototype.wrap = function (set) {
    if (this.A === null) this.A = set;else if (this.B === null) this.B = set;
  };
  CompositeSetWrapper.prototype.has = function (key) {
    if (this.A !== null && key in this.A) return true;
    if (this.B !== null && key in this.B) return true;
    return false;
  };

  /**
   * Function iterating over the given node's relevant neighbors to match
   * one of them using a predicated function.
   *
   * @param  {string}   type      - Type of neighbors.
   * @param  {string}   direction - Direction.
   * @param  {any}      nodeData  - Target node's data.
   * @param  {function} callback  - Callback to use.
   */
  function forEachInObjectOnce(breakable, visited, nodeData, object, callback) {
    for (var k in object) {
      var edgeData = object[k];
      var sourceData = edgeData.source;
      var targetData = edgeData.target;
      var neighborData = sourceData === nodeData ? targetData : sourceData;
      if (visited && visited.has(neighborData.key)) continue;
      var shouldBreak = callback(neighborData.key, neighborData.attributes);
      if (breakable && shouldBreak) return neighborData.key;
    }
    return;
  }
  function forEachNeighbor(breakable, type, direction, nodeData, callback) {
    // If we want only undirected or in or out, we can roll some optimizations
    if (type !== 'mixed') {
      if (type === 'undirected') return forEachInObjectOnce(breakable, null, nodeData, nodeData.undirected, callback);
      if (typeof direction === 'string') return forEachInObjectOnce(breakable, null, nodeData, nodeData[direction], callback);
    }

    // Else we need to keep a set of neighbors not to return duplicates
    // We cheat by querying the other adjacencies
    var visited = new CompositeSetWrapper();
    var found;
    if (type !== 'undirected') {
      if (direction !== 'out') {
        found = forEachInObjectOnce(breakable, null, nodeData, nodeData["in"], callback);
        if (breakable && found) return found;
        visited.wrap(nodeData["in"]);
      }
      if (direction !== 'in') {
        found = forEachInObjectOnce(breakable, visited, nodeData, nodeData.out, callback);
        if (breakable && found) return found;
        visited.wrap(nodeData.out);
      }
    }
    if (type !== 'directed') {
      found = forEachInObjectOnce(breakable, visited, nodeData, nodeData.undirected, callback);
      if (breakable && found) return found;
    }
    return;
  }

  /**
   * Function creating an array of relevant neighbors for the given node.
   *
   * @param  {string}       type      - Type of neighbors.
   * @param  {string}       direction - Direction.
   * @param  {any}          nodeData  - Target node's data.
   * @return {Array}                  - The list of neighbors.
   */
  function createNeighborArrayForNode(type, direction, nodeData) {
    // If we want only undirected or in or out, we can roll some optimizations
    if (type !== 'mixed') {
      if (type === 'undirected') return Object.keys(nodeData.undirected);
      if (typeof direction === 'string') return Object.keys(nodeData[direction]);
    }
    var neighbors = [];
    forEachNeighbor(false, type, direction, nodeData, function (key) {
      neighbors.push(key);
    });
    return neighbors;
  }

  /**
   * Function returning an iterator over the given node's relevant neighbors.
   *
   * @param  {string}   type      - Type of neighbors.
   * @param  {string}   direction - Direction.
   * @param  {any}      nodeData  - Target node's data.
   * @return {Iterator}
   */
  function createDedupedObjectIterator(visited, nodeData, object) {
    var keys = Object.keys(object);
    var l = keys.length;
    var i = 0;
    return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
      return this;
    }), "next", function next() {
      var neighborData = null;
      do {
        if (i >= l) {
          if (visited) visited.wrap(object);
          return {
            done: true
          };
        }
        var edgeData = object[keys[i++]];
        var sourceData = edgeData.source;
        var targetData = edgeData.target;
        neighborData = sourceData === nodeData ? targetData : sourceData;
        if (visited && visited.has(neighborData.key)) {
          neighborData = null;
          continue;
        }
      } while (neighborData === null);
      return {
        done: false,
        value: {
          neighbor: neighborData.key,
          attributes: neighborData.attributes
        }
      };
    });
  }
  function createNeighborIterator(type, direction, nodeData) {
    // If we want only undirected or in or out, we can roll some optimizations
    if (type !== 'mixed') {
      if (type === 'undirected') return createDedupedObjectIterator(null, nodeData, nodeData.undirected);
      if (typeof direction === 'string') return createDedupedObjectIterator(null, nodeData, nodeData[direction]);
    }
    var iterator = emptyIterator();

    // Else we need to keep a set of neighbors not to return duplicates
    // We cheat by querying the other adjacencies
    var visited = new CompositeSetWrapper();
    if (type !== 'undirected') {
      if (direction !== 'out') {
        iterator = chain(iterator, createDedupedObjectIterator(visited, nodeData, nodeData["in"]));
      }
      if (direction !== 'in') {
        iterator = chain(iterator, createDedupedObjectIterator(visited, nodeData, nodeData.out));
      }
    }
    if (type !== 'directed') {
      iterator = chain(iterator, createDedupedObjectIterator(visited, nodeData, nodeData.undirected));
    }
    return iterator;
  }

  /**
   * Function attaching a neighbors array creator method to the Graph prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachNeighborArrayCreator(Class, description) {
    var name = description.name,
      type = description.type,
      direction = description.direction;

    /**
     * Function returning an array of certain neighbors.
     *
     * @param  {any}   node   - Target node.
     * @return {array} - The neighbors of neighbors.
     *
     * @throws {Error} - Will throw if node is not found in the graph.
     */
    Class.prototype[name] = function (node) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return [];
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (typeof nodeData === 'undefined') throw new NotFoundGraphError("Graph.".concat(name, ": could not find the \"").concat(node, "\" node in the graph."));

      // Here, we want to iterate over a node's relevant neighbors
      return createNeighborArrayForNode(type === 'mixed' ? this.type : type, direction, nodeData);
    };
  }

  /**
   * Function attaching a neighbors callback iterator method to the Graph prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachForEachNeighbor(Class, description) {
    var name = description.name,
      type = description.type,
      direction = description.direction;
    var forEachName = 'forEach' + name[0].toUpperCase() + name.slice(1, -1);

    /**
     * Function iterating over all the relevant neighbors using a callback.
     *
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    Class.prototype[forEachName] = function (node, callback) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return;
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (typeof nodeData === 'undefined') throw new NotFoundGraphError("Graph.".concat(forEachName, ": could not find the \"").concat(node, "\" node in the graph."));

      // Here, we want to iterate over a node's relevant neighbors
      forEachNeighbor(false, type === 'mixed' ? this.type : type, direction, nodeData, callback);
    };

    /**
     * Function mapping the relevant neighbors using a callback.
     *
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var mapName = 'map' + name[0].toUpperCase() + name.slice(1);
    Class.prototype[mapName] = function (node, callback) {
      // TODO: optimize when size is known beforehand
      var result = [];
      this[forEachName](node, function (n, a) {
        result.push(callback(n, a));
      });
      return result;
    };

    /**
     * Function filtering the relevant neighbors using a callback.
     *
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var filterName = 'filter' + name[0].toUpperCase() + name.slice(1);
    Class.prototype[filterName] = function (node, callback) {
      var result = [];
      this[forEachName](node, function (n, a) {
        if (callback(n, a)) result.push(n);
      });
      return result;
    };

    /**
     * Function reducing the relevant neighbors using a callback.
     *
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var reduceName = 'reduce' + name[0].toUpperCase() + name.slice(1);
    Class.prototype[reduceName] = function (node, callback, initialValue) {
      if (arguments.length < 3) throw new InvalidArgumentsGraphError("Graph.".concat(reduceName, ": missing initial value. You must provide it because the callback takes more than one argument and we cannot infer the initial value from the first iteration, as you could with a simple array."));
      var accumulator = initialValue;
      this[forEachName](node, function (n, a) {
        accumulator = callback(accumulator, n, a);
      });
      return accumulator;
    };
  }

  /**
   * Function attaching a breakable neighbors callback iterator method to the
   * Graph prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachFindNeighbor(Class, description) {
    var name = description.name,
      type = description.type,
      direction = description.direction;
    var capitalizedSingular = name[0].toUpperCase() + name.slice(1, -1);
    var findName = 'find' + capitalizedSingular;

    /**
     * Function iterating over all the relevant neighbors using a callback.
     *
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     * @return {undefined}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    Class.prototype[findName] = function (node, callback) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return;
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (typeof nodeData === 'undefined') throw new NotFoundGraphError("Graph.".concat(findName, ": could not find the \"").concat(node, "\" node in the graph."));

      // Here, we want to iterate over a node's relevant neighbors
      return forEachNeighbor(true, type === 'mixed' ? this.type : type, direction, nodeData, callback);
    };

    /**
     * Function iterating over all the relevant neighbors to find if any of them
     * matches the given predicate.
     *
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var someName = 'some' + capitalizedSingular;
    Class.prototype[someName] = function (node, callback) {
      var found = this[findName](node, callback);
      if (found) return true;
      return false;
    };

    /**
     * Function iterating over all the relevant neighbors to find if all of them
     * matche the given predicate.
     *
     * @param  {any}      node     - Target node.
     * @param  {function} callback - Callback to use.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    var everyName = 'every' + capitalizedSingular;
    Class.prototype[everyName] = function (node, callback) {
      var found = this[findName](node, function (n, a) {
        return !callback(n, a);
      });
      if (found) return false;
      return true;
    };
  }

  /**
   * Function attaching a neighbors callback iterator method to the Graph prototype.
   *
   * @param {function} Class       - Target class.
   * @param {object}   description - Method description.
   */
  function attachNeighborIteratorCreator(Class, description) {
    var name = description.name,
      type = description.type,
      direction = description.direction;
    var iteratorName = name.slice(0, -1) + 'Entries';

    /**
     * Function returning an iterator over all the relevant neighbors.
     *
     * @param  {any}      node     - Target node.
     * @return {Iterator}
     *
     * @throws {Error} - Will throw if there are too many arguments.
     */
    Class.prototype[iteratorName] = function (node) {
      // Early termination
      if (type !== 'mixed' && this.type !== 'mixed' && type !== this.type) return emptyIterator();
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (typeof nodeData === 'undefined') throw new NotFoundGraphError("Graph.".concat(iteratorName, ": could not find the \"").concat(node, "\" node in the graph."));

      // Here, we want to iterate over a node's relevant neighbors
      return createNeighborIterator(type === 'mixed' ? this.type : type, direction, nodeData);
    };
  }

  /**
   * Function attaching every neighbor iteration method to the Graph class.
   *
   * @param {function} Graph - Graph class.
   */
  function attachNeighborIterationMethods(Graph) {
    NEIGHBORS_ITERATION.forEach(function (description) {
      attachNeighborArrayCreator(Graph, description);
      attachForEachNeighbor(Graph, description);
      attachFindNeighbor(Graph, description);
      attachNeighborIteratorCreator(Graph, description);
    });
  }

  /**
   * Graphology Adjacency Iteration
   * ===============================
   *
   * Attaching some methods to the Graph class to be able to iterate over a
   * graph's adjacency.
   */

  /**
   * Function iterating over a simple graph's adjacency using a callback.
   *
   * @param {boolean}  breakable         - Can we break?
   * @param {boolean}  assymetric        - Whether to emit undirected edges only once.
   * @param {boolean}  disconnectedNodes - Whether to emit disconnected nodes.
   * @param {Graph}    graph             - Target Graph instance.
   * @param {callback} function          - Iteration callback.
   */
  function forEachAdjacency(breakable, assymetric, disconnectedNodes, graph, callback) {
    var iterator = graph._nodes.values();
    var type = graph.type;
    var step, sourceData, neighbor, adj, edgeData, targetData, shouldBreak;
    while (step = iterator.next(), step.done !== true) {
      var hasEdges = false;
      sourceData = step.value;
      if (type !== 'undirected') {
        adj = sourceData.out;
        for (neighbor in adj) {
          edgeData = adj[neighbor];
          do {
            targetData = edgeData.target;
            hasEdges = true;
            shouldBreak = callback(sourceData.key, targetData.key, sourceData.attributes, targetData.attributes, edgeData.key, edgeData.attributes, edgeData.undirected);
            if (breakable && shouldBreak) return edgeData;
            edgeData = edgeData.next;
          } while (edgeData);
        }
      }
      if (type !== 'directed') {
        adj = sourceData.undirected;
        for (neighbor in adj) {
          if (assymetric && sourceData.key > neighbor) continue;
          edgeData = adj[neighbor];
          do {
            targetData = edgeData.target;
            if (targetData.key !== neighbor) targetData = edgeData.source;
            hasEdges = true;
            shouldBreak = callback(sourceData.key, targetData.key, sourceData.attributes, targetData.attributes, edgeData.key, edgeData.attributes, edgeData.undirected);
            if (breakable && shouldBreak) return edgeData;
            edgeData = edgeData.next;
          } while (edgeData);
        }
      }
      if (disconnectedNodes && !hasEdges) {
        shouldBreak = callback(sourceData.key, null, sourceData.attributes, null, null, null, null);
        if (breakable && shouldBreak) return null;
      }
    }
    return;
  }

  /**
   * Graphology Serialization Utilities
   * ===================================
   *
   * Collection of functions used by the graph serialization schemes.
   */

  /**
   * Formats internal node data into a serialized node.
   *
   * @param  {any}    key  - The node's key.
   * @param  {object} data - Internal node's data.
   * @return {array}       - The serialized node.
   */
  function serializeNode(key, data) {
    var serialized = {
      key: key
    };
    if (!isEmpty(data.attributes)) serialized.attributes = assign({}, data.attributes);
    return serialized;
  }

  /**
   * Formats internal edge data into a serialized edge.
   *
   * @param  {string} type - The graph's type.
   * @param  {any}    key  - The edge's key.
   * @param  {object} data - Internal edge's data.
   * @return {array}       - The serialized edge.
   */
  function serializeEdge(type, key, data) {
    var serialized = {
      key: key,
      source: data.source.key,
      target: data.target.key
    };
    if (!isEmpty(data.attributes)) serialized.attributes = assign({}, data.attributes);
    if (type === 'mixed' && data.undirected) serialized.undirected = true;
    return serialized;
  }

  /**
   * Checks whether the given value is a serialized node.
   *
   * @param  {mixed} value - Target value.
   * @return {string|null}
   */
  function validateSerializedNode(value) {
    if (!isPlainObject(value)) throw new InvalidArgumentsGraphError('Graph.import: invalid serialized node. A serialized node should be a plain object with at least a "key" property.');
    if (!('key' in value)) throw new InvalidArgumentsGraphError('Graph.import: serialized node is missing its key.');
    if ('attributes' in value && (!isPlainObject(value.attributes) || value.attributes === null)) throw new InvalidArgumentsGraphError('Graph.import: invalid attributes. Attributes should be a plain object, null or omitted.');
  }

  /**
   * Checks whether the given value is a serialized edge.
   *
   * @param  {mixed} value - Target value.
   * @return {string|null}
   */
  function validateSerializedEdge(value) {
    if (!isPlainObject(value)) throw new InvalidArgumentsGraphError('Graph.import: invalid serialized edge. A serialized edge should be a plain object with at least a "source" & "target" property.');
    if (!('source' in value)) throw new InvalidArgumentsGraphError('Graph.import: serialized edge is missing its source.');
    if (!('target' in value)) throw new InvalidArgumentsGraphError('Graph.import: serialized edge is missing its target.');
    if ('attributes' in value && (!isPlainObject(value.attributes) || value.attributes === null)) throw new InvalidArgumentsGraphError('Graph.import: invalid attributes. Attributes should be a plain object, null or omitted.');
    if ('undirected' in value && typeof value.undirected !== 'boolean') throw new InvalidArgumentsGraphError('Graph.import: invalid undirectedness information. Undirected should be boolean or omitted.');
  }

  /**
   * Constants.
   */
  var INSTANCE_ID = incrementalIdStartingFromRandomByte();

  /**
   * Enums.
   */
  var TYPES = new Set(['directed', 'undirected', 'mixed']);
  var EMITTER_PROPS = new Set(['domain', '_events', '_eventsCount', '_maxListeners']);
  var EDGE_ADD_METHODS = [{
    name: function name(verb) {
      return "".concat(verb, "Edge");
    },
    generateKey: true
  }, {
    name: function name(verb) {
      return "".concat(verb, "DirectedEdge");
    },
    generateKey: true,
    type: 'directed'
  }, {
    name: function name(verb) {
      return "".concat(verb, "UndirectedEdge");
    },
    generateKey: true,
    type: 'undirected'
  }, {
    name: function name(verb) {
      return "".concat(verb, "EdgeWithKey");
    }
  }, {
    name: function name(verb) {
      return "".concat(verb, "DirectedEdgeWithKey");
    },
    type: 'directed'
  }, {
    name: function name(verb) {
      return "".concat(verb, "UndirectedEdgeWithKey");
    },
    type: 'undirected'
  }];

  /**
   * Default options.
   */
  var DEFAULTS = {
    allowSelfLoops: true,
    multi: false,
    type: 'mixed'
  };

  /**
   * Abstract functions used by the Graph class for various methods.
   */

  /**
   * Internal method used to add a node to the given graph
   *
   * @param  {Graph}   graph           - Target graph.
   * @param  {any}     node            - The node's key.
   * @param  {object}  [attributes]    - Optional attributes.
   * @return {NodeData}                - Created node data.
   */
  function _addNode(graph, node, attributes) {
    if (attributes && !isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.addNode: invalid attributes. Expecting an object but got \"".concat(attributes, "\""));

    // String coercion
    node = '' + node;
    attributes = attributes || {};
    if (graph._nodes.has(node)) throw new UsageGraphError("Graph.addNode: the \"".concat(node, "\" node already exist in the graph."));
    var data = new graph.NodeDataClass(node, attributes);

    // Adding the node to internal register
    graph._nodes.set(node, data);

    // Emitting
    graph.emit('nodeAdded', {
      key: node,
      attributes: attributes
    });
    return data;
  }

  /**
   * Same as the above but without sanity checks because we call this in contexts
   * where necessary checks were already done.
   */
  function unsafeAddNode(graph, node, attributes) {
    var data = new graph.NodeDataClass(node, attributes);
    graph._nodes.set(node, data);
    graph.emit('nodeAdded', {
      key: node,
      attributes: attributes
    });
    return data;
  }

  /**
   * Internal method used to add an arbitrary edge to the given graph.
   *
   * @param  {Graph}   graph           - Target graph.
   * @param  {string}  name            - Name of the child method for errors.
   * @param  {boolean} mustGenerateKey - Should the graph generate an id?
   * @param  {boolean} undirected      - Whether the edge is undirected.
   * @param  {any}     edge            - The edge's key.
   * @param  {any}     source          - The source node.
   * @param  {any}     target          - The target node.
   * @param  {object}  [attributes]    - Optional attributes.
   * @return {any}                     - The edge.
   *
   * @throws {Error} - Will throw if the graph is of the wrong type.
   * @throws {Error} - Will throw if the given attributes are not an object.
   * @throws {Error} - Will throw if source or target doesn't exist.
   * @throws {Error} - Will throw if the edge already exist.
   */
  function addEdge(graph, name, mustGenerateKey, undirected, edge, source, target, attributes) {
    // Checking validity of operation
    if (!undirected && graph.type === 'undirected') throw new UsageGraphError("Graph.".concat(name, ": you cannot add a directed edge to an undirected graph. Use the #.addEdge or #.addUndirectedEdge instead."));
    if (undirected && graph.type === 'directed') throw new UsageGraphError("Graph.".concat(name, ": you cannot add an undirected edge to a directed graph. Use the #.addEdge or #.addDirectedEdge instead."));
    if (attributes && !isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.".concat(name, ": invalid attributes. Expecting an object but got \"").concat(attributes, "\""));

    // Coercion of source & target:
    source = '' + source;
    target = '' + target;
    attributes = attributes || {};
    if (!graph.allowSelfLoops && source === target) throw new UsageGraphError("Graph.".concat(name, ": source & target are the same (\"").concat(source, "\"), thus creating a loop explicitly forbidden by this graph 'allowSelfLoops' option set to false."));
    var sourceData = graph._nodes.get(source),
      targetData = graph._nodes.get(target);
    if (!sourceData) throw new NotFoundGraphError("Graph.".concat(name, ": source node \"").concat(source, "\" not found."));
    if (!targetData) throw new NotFoundGraphError("Graph.".concat(name, ": target node \"").concat(target, "\" not found."));

    // Must the graph generate an id for this edge?
    var eventData = {
      key: null,
      undirected: undirected,
      source: source,
      target: target,
      attributes: attributes
    };
    if (mustGenerateKey) {
      // NOTE: in this case we can guarantee that the key does not already
      // exist and is already correctly casted as a string
      edge = graph._edgeKeyGenerator();
    } else {
      // Coercion of edge key
      edge = '' + edge;

      // Here, we have a key collision
      if (graph._edges.has(edge)) throw new UsageGraphError("Graph.".concat(name, ": the \"").concat(edge, "\" edge already exists in the graph."));
    }

    // Here, we might have a source / target collision
    if (!graph.multi && (undirected ? typeof sourceData.undirected[target] !== 'undefined' : typeof sourceData.out[target] !== 'undefined')) {
      throw new UsageGraphError("Graph.".concat(name, ": an edge linking \"").concat(source, "\" to \"").concat(target, "\" already exists. If you really want to add multiple edges linking those nodes, you should create a multi graph by using the 'multi' option."));
    }

    // Storing some data
    var edgeData = new EdgeData(undirected, edge, sourceData, targetData, attributes);

    // Adding the edge to the internal register
    graph._edges.set(edge, edgeData);

    // Incrementing node degree counters
    var isSelfLoop = source === target;
    if (undirected) {
      sourceData.undirectedDegree++;
      targetData.undirectedDegree++;
      if (isSelfLoop) {
        sourceData.undirectedLoops++;
        graph._undirectedSelfLoopCount++;
      }
    } else {
      sourceData.outDegree++;
      targetData.inDegree++;
      if (isSelfLoop) {
        sourceData.directedLoops++;
        graph._directedSelfLoopCount++;
      }
    }

    // Updating relevant index
    if (graph.multi) edgeData.attachMulti();else edgeData.attach();
    if (undirected) graph._undirectedSize++;else graph._directedSize++;

    // Emitting
    eventData.key = edge;
    graph.emit('edgeAdded', eventData);
    return edge;
  }

  /**
   * Internal method used to add an arbitrary edge to the given graph.
   *
   * @param  {Graph}   graph           - Target graph.
   * @param  {string}  name            - Name of the child method for errors.
   * @param  {boolean} mustGenerateKey - Should the graph generate an id?
   * @param  {boolean} undirected      - Whether the edge is undirected.
   * @param  {any}     edge            - The edge's key.
   * @param  {any}     source          - The source node.
   * @param  {any}     target          - The target node.
   * @param  {object}  [attributes]    - Optional attributes.
   * @param  {boolean} [asUpdater]       - Are we updating or merging?
   * @return {any}                     - The edge.
   *
   * @throws {Error} - Will throw if the graph is of the wrong type.
   * @throws {Error} - Will throw if the given attributes are not an object.
   * @throws {Error} - Will throw if source or target doesn't exist.
   * @throws {Error} - Will throw if the edge already exist.
   */
  function mergeEdge(graph, name, mustGenerateKey, undirected, edge, source, target, attributes, asUpdater) {
    // Checking validity of operation
    if (!undirected && graph.type === 'undirected') throw new UsageGraphError("Graph.".concat(name, ": you cannot merge/update a directed edge to an undirected graph. Use the #.mergeEdge/#.updateEdge or #.addUndirectedEdge instead."));
    if (undirected && graph.type === 'directed') throw new UsageGraphError("Graph.".concat(name, ": you cannot merge/update an undirected edge to a directed graph. Use the #.mergeEdge/#.updateEdge or #.addDirectedEdge instead."));
    if (attributes) {
      if (asUpdater) {
        if (typeof attributes !== 'function') throw new InvalidArgumentsGraphError("Graph.".concat(name, ": invalid updater function. Expecting a function but got \"").concat(attributes, "\""));
      } else {
        if (!isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.".concat(name, ": invalid attributes. Expecting an object but got \"").concat(attributes, "\""));
      }
    }

    // Coercion of source & target:
    source = '' + source;
    target = '' + target;
    var updater;
    if (asUpdater) {
      updater = attributes;
      attributes = undefined;
    }
    if (!graph.allowSelfLoops && source === target) throw new UsageGraphError("Graph.".concat(name, ": source & target are the same (\"").concat(source, "\"), thus creating a loop explicitly forbidden by this graph 'allowSelfLoops' option set to false."));
    var sourceData = graph._nodes.get(source);
    var targetData = graph._nodes.get(target);
    var edgeData;

    // Do we need to handle duplicate?
    var alreadyExistingEdgeData;
    if (!mustGenerateKey) {
      edgeData = graph._edges.get(edge);
      if (edgeData) {
        // Here, we need to ensure, if the user gave a key, that source & target
        // are consistent
        if (edgeData.source.key !== source || edgeData.target.key !== target) {
          // If source or target inconsistent
          if (!undirected || edgeData.source.key !== target || edgeData.target.key !== source) {
            // If directed, or source/target aren't flipped
            throw new UsageGraphError("Graph.".concat(name, ": inconsistency detected when attempting to merge the \"").concat(edge, "\" edge with \"").concat(source, "\" source & \"").concat(target, "\" target vs. (\"").concat(edgeData.source.key, "\", \"").concat(edgeData.target.key, "\")."));
          }
        }
        alreadyExistingEdgeData = edgeData;
      }
    }

    // Here, we might have a source / target collision
    if (!alreadyExistingEdgeData && !graph.multi && sourceData) {
      alreadyExistingEdgeData = undirected ? sourceData.undirected[target] : sourceData.out[target];
    }

    // Handling duplicates
    if (alreadyExistingEdgeData) {
      var info = [alreadyExistingEdgeData.key, false, false, false];

      // We can skip the attribute merging part if the user did not provide them
      if (asUpdater ? !updater : !attributes) return info;

      // Updating the attributes
      if (asUpdater) {
        var oldAttributes = alreadyExistingEdgeData.attributes;
        alreadyExistingEdgeData.attributes = updater(oldAttributes);
        graph.emit('edgeAttributesUpdated', {
          type: 'replace',
          key: alreadyExistingEdgeData.key,
          attributes: alreadyExistingEdgeData.attributes
        });
      }

      // Merging the attributes
      else {
        assign(alreadyExistingEdgeData.attributes, attributes);
        graph.emit('edgeAttributesUpdated', {
          type: 'merge',
          key: alreadyExistingEdgeData.key,
          attributes: alreadyExistingEdgeData.attributes,
          data: attributes
        });
      }
      return info;
    }
    attributes = attributes || {};
    if (asUpdater && updater) attributes = updater(attributes);

    // Must the graph generate an id for this edge?
    var eventData = {
      key: null,
      undirected: undirected,
      source: source,
      target: target,
      attributes: attributes
    };
    if (mustGenerateKey) {
      // NOTE: in this case we can guarantee that the key does not already
      // exist and is already correctly casted as a string
      edge = graph._edgeKeyGenerator();
    } else {
      // Coercion of edge key
      edge = '' + edge;

      // Here, we have a key collision
      if (graph._edges.has(edge)) throw new UsageGraphError("Graph.".concat(name, ": the \"").concat(edge, "\" edge already exists in the graph."));
    }
    var sourceWasAdded = false;
    var targetWasAdded = false;
    if (!sourceData) {
      sourceData = unsafeAddNode(graph, source, {});
      sourceWasAdded = true;
      if (source === target) {
        targetData = sourceData;
        targetWasAdded = true;
      }
    }
    if (!targetData) {
      targetData = unsafeAddNode(graph, target, {});
      targetWasAdded = true;
    }

    // Storing some data
    edgeData = new EdgeData(undirected, edge, sourceData, targetData, attributes);

    // Adding the edge to the internal register
    graph._edges.set(edge, edgeData);

    // Incrementing node degree counters
    var isSelfLoop = source === target;
    if (undirected) {
      sourceData.undirectedDegree++;
      targetData.undirectedDegree++;
      if (isSelfLoop) {
        sourceData.undirectedLoops++;
        graph._undirectedSelfLoopCount++;
      }
    } else {
      sourceData.outDegree++;
      targetData.inDegree++;
      if (isSelfLoop) {
        sourceData.directedLoops++;
        graph._directedSelfLoopCount++;
      }
    }

    // Updating relevant index
    if (graph.multi) edgeData.attachMulti();else edgeData.attach();
    if (undirected) graph._undirectedSize++;else graph._directedSize++;

    // Emitting
    eventData.key = edge;
    graph.emit('edgeAdded', eventData);
    return [edge, true, sourceWasAdded, targetWasAdded];
  }

  /**
   * Internal method used to drop an edge.
   *
   * @param  {Graph}    graph    - Target graph.
   * @param  {EdgeData} edgeData - Data of the edge to drop.
   */
  function dropEdgeFromData(graph, edgeData) {
    // Dropping the edge from the register
    graph._edges["delete"](edgeData.key);

    // Updating related degrees
    var sourceData = edgeData.source,
      targetData = edgeData.target,
      attributes = edgeData.attributes;
    var undirected = edgeData.undirected;
    var isSelfLoop = sourceData === targetData;
    if (undirected) {
      sourceData.undirectedDegree--;
      targetData.undirectedDegree--;
      if (isSelfLoop) {
        sourceData.undirectedLoops--;
        graph._undirectedSelfLoopCount--;
      }
    } else {
      sourceData.outDegree--;
      targetData.inDegree--;
      if (isSelfLoop) {
        sourceData.directedLoops--;
        graph._directedSelfLoopCount--;
      }
    }

    // Clearing index
    if (graph.multi) edgeData.detachMulti();else edgeData.detach();
    if (undirected) graph._undirectedSize--;else graph._directedSize--;

    // Emitting
    graph.emit('edgeDropped', {
      key: edgeData.key,
      attributes: attributes,
      source: sourceData.key,
      target: targetData.key,
      undirected: undirected
    });
  }

  /**
   * Graph class
   *
   * @constructor
   * @param  {object}  [options] - Options:
   * @param  {boolean}   [allowSelfLoops] - Allow self loops?
   * @param  {string}    [type]           - Type of the graph.
   * @param  {boolean}   [map]            - Allow references as keys?
   * @param  {boolean}   [multi]          - Allow parallel edges?
   *
   * @throws {Error} - Will throw if the arguments are not valid.
   */
  var Graph = /*#__PURE__*/function (_EventEmitter) {
    _inheritsLoose(Graph, _EventEmitter);
    function Graph(options) {
      var _this;
      _this = _EventEmitter.call(this) || this;

      //-- Solving options
      options = assign({}, DEFAULTS, options);

      // Enforcing options validity
      if (typeof options.multi !== 'boolean') throw new InvalidArgumentsGraphError("Graph.constructor: invalid 'multi' option. Expecting a boolean but got \"".concat(options.multi, "\"."));
      if (!TYPES.has(options.type)) throw new InvalidArgumentsGraphError("Graph.constructor: invalid 'type' option. Should be one of \"mixed\", \"directed\" or \"undirected\" but got \"".concat(options.type, "\"."));
      if (typeof options.allowSelfLoops !== 'boolean') throw new InvalidArgumentsGraphError("Graph.constructor: invalid 'allowSelfLoops' option. Expecting a boolean but got \"".concat(options.allowSelfLoops, "\"."));

      //-- Private properties

      // Utilities
      var NodeDataClass = options.type === 'mixed' ? MixedNodeData : options.type === 'directed' ? DirectedNodeData : UndirectedNodeData;
      privateProperty(_assertThisInitialized(_this), 'NodeDataClass', NodeDataClass);

      // Internal edge key generator

      // NOTE: this internal generator produce keys that are strings
      // composed of a weird prefix, an incremental instance id starting from
      // a random byte and finally an internal instance incremental id.
      // All this to avoid intra-frame and cross-frame adversarial inputs
      // that can force a single #.addEdge call to degenerate into a O(n)
      // available key search loop.

      // It also ensures that automatically generated edge keys are unlikely
      // to produce collisions with arbitrary keys given by users.
      var instancePrefix = 'geid_' + INSTANCE_ID() + '_';
      var edgeId = 0;
      var edgeKeyGenerator = function edgeKeyGenerator() {
        var availableEdgeKey;
        do {
          availableEdgeKey = instancePrefix + edgeId++;
        } while (_this._edges.has(availableEdgeKey));
        return availableEdgeKey;
      };

      // Indexes
      privateProperty(_assertThisInitialized(_this), '_attributes', {});
      privateProperty(_assertThisInitialized(_this), '_nodes', new Map());
      privateProperty(_assertThisInitialized(_this), '_edges', new Map());
      privateProperty(_assertThisInitialized(_this), '_directedSize', 0);
      privateProperty(_assertThisInitialized(_this), '_undirectedSize', 0);
      privateProperty(_assertThisInitialized(_this), '_directedSelfLoopCount', 0);
      privateProperty(_assertThisInitialized(_this), '_undirectedSelfLoopCount', 0);
      privateProperty(_assertThisInitialized(_this), '_edgeKeyGenerator', edgeKeyGenerator);

      // Options
      privateProperty(_assertThisInitialized(_this), '_options', options);

      // Emitter properties
      EMITTER_PROPS.forEach(function (prop) {
        return privateProperty(_assertThisInitialized(_this), prop, _this[prop]);
      });

      //-- Properties readers
      readOnlyProperty(_assertThisInitialized(_this), 'order', function () {
        return _this._nodes.size;
      });
      readOnlyProperty(_assertThisInitialized(_this), 'size', function () {
        return _this._edges.size;
      });
      readOnlyProperty(_assertThisInitialized(_this), 'directedSize', function () {
        return _this._directedSize;
      });
      readOnlyProperty(_assertThisInitialized(_this), 'undirectedSize', function () {
        return _this._undirectedSize;
      });
      readOnlyProperty(_assertThisInitialized(_this), 'selfLoopCount', function () {
        return _this._directedSelfLoopCount + _this._undirectedSelfLoopCount;
      });
      readOnlyProperty(_assertThisInitialized(_this), 'directedSelfLoopCount', function () {
        return _this._directedSelfLoopCount;
      });
      readOnlyProperty(_assertThisInitialized(_this), 'undirectedSelfLoopCount', function () {
        return _this._undirectedSelfLoopCount;
      });
      readOnlyProperty(_assertThisInitialized(_this), 'multi', _this._options.multi);
      readOnlyProperty(_assertThisInitialized(_this), 'type', _this._options.type);
      readOnlyProperty(_assertThisInitialized(_this), 'allowSelfLoops', _this._options.allowSelfLoops);
      readOnlyProperty(_assertThisInitialized(_this), 'implementation', function () {
        return 'graphology';
      });
      return _this;
    }
    var _proto = Graph.prototype;
    _proto._resetInstanceCounters = function _resetInstanceCounters() {
      this._directedSize = 0;
      this._undirectedSize = 0;
      this._directedSelfLoopCount = 0;
      this._undirectedSelfLoopCount = 0;
    }

    /**---------------------------------------------------------------------------
     * Read
     **---------------------------------------------------------------------------
     */

    /**
     * Method returning whether the given node is found in the graph.
     *
     * @param  {any}     node - The node.
     * @return {boolean}
     */;
    _proto.hasNode = function hasNode(node) {
      return this._nodes.has('' + node);
    }

    /**
     * Method returning whether the given directed edge is found in the graph.
     *
     * Arity 1:
     * @param  {any}     edge - The edge's key.
     *
     * Arity 2:
     * @param  {any}     source - The edge's source.
     * @param  {any}     target - The edge's target.
     *
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the arguments are invalid.
     */;
    _proto.hasDirectedEdge = function hasDirectedEdge(source, target) {
      // Early termination
      if (this.type === 'undirected') return false;
      if (arguments.length === 1) {
        var edge = '' + source;
        var edgeData = this._edges.get(edge);
        return !!edgeData && !edgeData.undirected;
      } else if (arguments.length === 2) {
        source = '' + source;
        target = '' + target;

        // If the node source or the target is not in the graph we break
        var nodeData = this._nodes.get(source);
        if (!nodeData) return false;

        // Is there a directed edge pointing toward target?
        return nodeData.out.hasOwnProperty(target);
      }
      throw new InvalidArgumentsGraphError("Graph.hasDirectedEdge: invalid arity (".concat(arguments.length, ", instead of 1 or 2). You can either ask for an edge id or for the existence of an edge between a source & a target."));
    }

    /**
     * Method returning whether the given undirected edge is found in the graph.
     *
     * Arity 1:
     * @param  {any}     edge - The edge's key.
     *
     * Arity 2:
     * @param  {any}     source - The edge's source.
     * @param  {any}     target - The edge's target.
     *
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the arguments are invalid.
     */;
    _proto.hasUndirectedEdge = function hasUndirectedEdge(source, target) {
      // Early termination
      if (this.type === 'directed') return false;
      if (arguments.length === 1) {
        var edge = '' + source;
        var edgeData = this._edges.get(edge);
        return !!edgeData && edgeData.undirected;
      } else if (arguments.length === 2) {
        source = '' + source;
        target = '' + target;

        // If the node source or the target is not in the graph we break
        var nodeData = this._nodes.get(source);
        if (!nodeData) return false;

        // Is there a directed edge pointing toward target?
        return nodeData.undirected.hasOwnProperty(target);
      }
      throw new InvalidArgumentsGraphError("Graph.hasDirectedEdge: invalid arity (".concat(arguments.length, ", instead of 1 or 2). You can either ask for an edge id or for the existence of an edge between a source & a target."));
    }

    /**
     * Method returning whether the given edge is found in the graph.
     *
     * Arity 1:
     * @param  {any}     edge - The edge's key.
     *
     * Arity 2:
     * @param  {any}     source - The edge's source.
     * @param  {any}     target - The edge's target.
     *
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the arguments are invalid.
     */;
    _proto.hasEdge = function hasEdge(source, target) {
      if (arguments.length === 1) {
        var edge = '' + source;
        return this._edges.has(edge);
      } else if (arguments.length === 2) {
        source = '' + source;
        target = '' + target;

        // If the node source or the target is not in the graph we break
        var nodeData = this._nodes.get(source);
        if (!nodeData) return false;

        // Is there a directed edge pointing toward target?
        return typeof nodeData.out !== 'undefined' && nodeData.out.hasOwnProperty(target) || typeof nodeData.undirected !== 'undefined' && nodeData.undirected.hasOwnProperty(target);
      }
      throw new InvalidArgumentsGraphError("Graph.hasEdge: invalid arity (".concat(arguments.length, ", instead of 1 or 2). You can either ask for an edge id or for the existence of an edge between a source & a target."));
    }

    /**
     * Method returning the edge matching source & target in a directed fashion.
     *
     * @param  {any} source - The edge's source.
     * @param  {any} target - The edge's target.
     *
     * @return {any|undefined}
     *
     * @throws {Error} - Will throw if the graph is multi.
     * @throws {Error} - Will throw if source or target doesn't exist.
     */;
    _proto.directedEdge = function directedEdge(source, target) {
      if (this.type === 'undirected') return;
      source = '' + source;
      target = '' + target;
      if (this.multi) throw new UsageGraphError('Graph.directedEdge: this method is irrelevant with multigraphs since there might be multiple edges between source & target. See #.directedEdges instead.');
      var sourceData = this._nodes.get(source);
      if (!sourceData) throw new NotFoundGraphError("Graph.directedEdge: could not find the \"".concat(source, "\" source node in the graph."));
      if (!this._nodes.has(target)) throw new NotFoundGraphError("Graph.directedEdge: could not find the \"".concat(target, "\" target node in the graph."));
      var edgeData = sourceData.out && sourceData.out[target] || undefined;
      if (edgeData) return edgeData.key;
    }

    /**
     * Method returning the edge matching source & target in a undirected fashion.
     *
     * @param  {any} source - The edge's source.
     * @param  {any} target - The edge's target.
     *
     * @return {any|undefined}
     *
     * @throws {Error} - Will throw if the graph is multi.
     * @throws {Error} - Will throw if source or target doesn't exist.
     */;
    _proto.undirectedEdge = function undirectedEdge(source, target) {
      if (this.type === 'directed') return;
      source = '' + source;
      target = '' + target;
      if (this.multi) throw new UsageGraphError('Graph.undirectedEdge: this method is irrelevant with multigraphs since there might be multiple edges between source & target. See #.undirectedEdges instead.');
      var sourceData = this._nodes.get(source);
      if (!sourceData) throw new NotFoundGraphError("Graph.undirectedEdge: could not find the \"".concat(source, "\" source node in the graph."));
      if (!this._nodes.has(target)) throw new NotFoundGraphError("Graph.undirectedEdge: could not find the \"".concat(target, "\" target node in the graph."));
      var edgeData = sourceData.undirected && sourceData.undirected[target] || undefined;
      if (edgeData) return edgeData.key;
    }

    /**
     * Method returning the edge matching source & target in a mixed fashion.
     *
     * @param  {any} source - The edge's source.
     * @param  {any} target - The edge's target.
     *
     * @return {any|undefined}
     *
     * @throws {Error} - Will throw if the graph is multi.
     * @throws {Error} - Will throw if source or target doesn't exist.
     */;
    _proto.edge = function edge(source, target) {
      if (this.multi) throw new UsageGraphError('Graph.edge: this method is irrelevant with multigraphs since there might be multiple edges between source & target. See #.edges instead.');
      source = '' + source;
      target = '' + target;
      var sourceData = this._nodes.get(source);
      if (!sourceData) throw new NotFoundGraphError("Graph.edge: could not find the \"".concat(source, "\" source node in the graph."));
      if (!this._nodes.has(target)) throw new NotFoundGraphError("Graph.edge: could not find the \"".concat(target, "\" target node in the graph."));
      var edgeData = sourceData.out && sourceData.out[target] || sourceData.undirected && sourceData.undirected[target] || undefined;
      if (edgeData) return edgeData.key;
    }

    /**
     * Method returning whether two nodes are directed neighbors.
     *
     * @param  {any}     node     - The node's key.
     * @param  {any}     neighbor - The neighbor's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.areDirectedNeighbors = function areDirectedNeighbors(node, neighbor) {
      node = '' + node;
      neighbor = '' + neighbor;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.areDirectedNeighbors: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return false;
      return neighbor in nodeData["in"] || neighbor in nodeData.out;
    }

    /**
     * Method returning whether two nodes are out neighbors.
     *
     * @param  {any}     node     - The node's key.
     * @param  {any}     neighbor - The neighbor's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.areOutNeighbors = function areOutNeighbors(node, neighbor) {
      node = '' + node;
      neighbor = '' + neighbor;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.areOutNeighbors: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return false;
      return neighbor in nodeData.out;
    }

    /**
     * Method returning whether two nodes are in neighbors.
     *
     * @param  {any}     node     - The node's key.
     * @param  {any}     neighbor - The neighbor's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.areInNeighbors = function areInNeighbors(node, neighbor) {
      node = '' + node;
      neighbor = '' + neighbor;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.areInNeighbors: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return false;
      return neighbor in nodeData["in"];
    }

    /**
     * Method returning whether two nodes are undirected neighbors.
     *
     * @param  {any}     node     - The node's key.
     * @param  {any}     neighbor - The neighbor's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.areUndirectedNeighbors = function areUndirectedNeighbors(node, neighbor) {
      node = '' + node;
      neighbor = '' + neighbor;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.areUndirectedNeighbors: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'directed') return false;
      return neighbor in nodeData.undirected;
    }

    /**
     * Method returning whether two nodes are neighbors.
     *
     * @param  {any}     node     - The node's key.
     * @param  {any}     neighbor - The neighbor's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.areNeighbors = function areNeighbors(node, neighbor) {
      node = '' + node;
      neighbor = '' + neighbor;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.areNeighbors: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type !== 'undirected') {
        if (neighbor in nodeData["in"] || neighbor in nodeData.out) return true;
      }
      if (this.type !== 'directed') {
        if (neighbor in nodeData.undirected) return true;
      }
      return false;
    }

    /**
     * Method returning whether two nodes are inbound neighbors.
     *
     * @param  {any}     node     - The node's key.
     * @param  {any}     neighbor - The neighbor's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.areInboundNeighbors = function areInboundNeighbors(node, neighbor) {
      node = '' + node;
      neighbor = '' + neighbor;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.areInboundNeighbors: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type !== 'undirected') {
        if (neighbor in nodeData["in"]) return true;
      }
      if (this.type !== 'directed') {
        if (neighbor in nodeData.undirected) return true;
      }
      return false;
    }

    /**
     * Method returning whether two nodes are outbound neighbors.
     *
     * @param  {any}     node     - The node's key.
     * @param  {any}     neighbor - The neighbor's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.areOutboundNeighbors = function areOutboundNeighbors(node, neighbor) {
      node = '' + node;
      neighbor = '' + neighbor;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.areOutboundNeighbors: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type !== 'undirected') {
        if (neighbor in nodeData.out) return true;
      }
      if (this.type !== 'directed') {
        if (neighbor in nodeData.undirected) return true;
      }
      return false;
    }

    /**
     * Method returning the given node's in degree.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.inDegree = function inDegree(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.inDegree: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return 0;
      return nodeData.inDegree;
    }

    /**
     * Method returning the given node's out degree.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.outDegree = function outDegree(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.outDegree: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return 0;
      return nodeData.outDegree;
    }

    /**
     * Method returning the given node's directed degree.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.directedDegree = function directedDegree(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.directedDegree: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return 0;
      return nodeData.inDegree + nodeData.outDegree;
    }

    /**
     * Method returning the given node's undirected degree.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.undirectedDegree = function undirectedDegree(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.undirectedDegree: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'directed') return 0;
      return nodeData.undirectedDegree;
    }

    /**
     * Method returning the given node's inbound degree.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's inbound degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.inboundDegree = function inboundDegree(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.inboundDegree: could not find the \"".concat(node, "\" node in the graph."));
      var degree = 0;
      if (this.type !== 'directed') {
        degree += nodeData.undirectedDegree;
      }
      if (this.type !== 'undirected') {
        degree += nodeData.inDegree;
      }
      return degree;
    }

    /**
     * Method returning the given node's outbound degree.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's outbound degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.outboundDegree = function outboundDegree(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.outboundDegree: could not find the \"".concat(node, "\" node in the graph."));
      var degree = 0;
      if (this.type !== 'directed') {
        degree += nodeData.undirectedDegree;
      }
      if (this.type !== 'undirected') {
        degree += nodeData.outDegree;
      }
      return degree;
    }

    /**
     * Method returning the given node's directed degree.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.degree = function degree(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.degree: could not find the \"".concat(node, "\" node in the graph."));
      var degree = 0;
      if (this.type !== 'directed') {
        degree += nodeData.undirectedDegree;
      }
      if (this.type !== 'undirected') {
        degree += nodeData.inDegree + nodeData.outDegree;
      }
      return degree;
    }

    /**
     * Method returning the given node's in degree without considering self loops.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.inDegreeWithoutSelfLoops = function inDegreeWithoutSelfLoops(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.inDegreeWithoutSelfLoops: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return 0;
      return nodeData.inDegree - nodeData.directedLoops;
    }

    /**
     * Method returning the given node's out degree without considering self loops.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.outDegreeWithoutSelfLoops = function outDegreeWithoutSelfLoops(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.outDegreeWithoutSelfLoops: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return 0;
      return nodeData.outDegree - nodeData.directedLoops;
    }

    /**
     * Method returning the given node's directed degree without considering self loops.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.directedDegreeWithoutSelfLoops = function directedDegreeWithoutSelfLoops(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.directedDegreeWithoutSelfLoops: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'undirected') return 0;
      return nodeData.inDegree + nodeData.outDegree - nodeData.directedLoops * 2;
    }

    /**
     * Method returning the given node's undirected degree without considering self loops.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's in degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.undirectedDegreeWithoutSelfLoops = function undirectedDegreeWithoutSelfLoops(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.undirectedDegreeWithoutSelfLoops: could not find the \"".concat(node, "\" node in the graph."));
      if (this.type === 'directed') return 0;
      return nodeData.undirectedDegree - nodeData.undirectedLoops * 2;
    }

    /**
     * Method returning the given node's inbound degree without considering self loops.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's inbound degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.inboundDegreeWithoutSelfLoops = function inboundDegreeWithoutSelfLoops(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.inboundDegreeWithoutSelfLoops: could not find the \"".concat(node, "\" node in the graph."));
      var degree = 0;
      var loops = 0;
      if (this.type !== 'directed') {
        degree += nodeData.undirectedDegree;
        loops += nodeData.undirectedLoops * 2;
      }
      if (this.type !== 'undirected') {
        degree += nodeData.inDegree;
        loops += nodeData.directedLoops;
      }
      return degree - loops;
    }

    /**
     * Method returning the given node's outbound degree without considering self loops.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's outbound degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.outboundDegreeWithoutSelfLoops = function outboundDegreeWithoutSelfLoops(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.outboundDegreeWithoutSelfLoops: could not find the \"".concat(node, "\" node in the graph."));
      var degree = 0;
      var loops = 0;
      if (this.type !== 'directed') {
        degree += nodeData.undirectedDegree;
        loops += nodeData.undirectedLoops * 2;
      }
      if (this.type !== 'undirected') {
        degree += nodeData.outDegree;
        loops += nodeData.directedLoops;
      }
      return degree - loops;
    }

    /**
     * Method returning the given node's directed degree without considering self loops.
     *
     * @param  {any}     node - The node's key.
     * @return {number}       - The node's degree.
     *
     * @throws {Error} - Will throw if the node isn't in the graph.
     */;
    _proto.degreeWithoutSelfLoops = function degreeWithoutSelfLoops(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.degreeWithoutSelfLoops: could not find the \"".concat(node, "\" node in the graph."));
      var degree = 0;
      var loops = 0;
      if (this.type !== 'directed') {
        degree += nodeData.undirectedDegree;
        loops += nodeData.undirectedLoops * 2;
      }
      if (this.type !== 'undirected') {
        degree += nodeData.inDegree + nodeData.outDegree;
        loops += nodeData.directedLoops * 2;
      }
      return degree - loops;
    }

    /**
     * Method returning the given edge's source.
     *
     * @param  {any} edge - The edge's key.
     * @return {any}      - The edge's source.
     *
     * @throws {Error} - Will throw if the edge isn't in the graph.
     */;
    _proto.source = function source(edge) {
      edge = '' + edge;
      var data = this._edges.get(edge);
      if (!data) throw new NotFoundGraphError("Graph.source: could not find the \"".concat(edge, "\" edge in the graph."));
      return data.source.key;
    }

    /**
     * Method returning the given edge's target.
     *
     * @param  {any} edge - The edge's key.
     * @return {any}      - The edge's target.
     *
     * @throws {Error} - Will throw if the edge isn't in the graph.
     */;
    _proto.target = function target(edge) {
      edge = '' + edge;
      var data = this._edges.get(edge);
      if (!data) throw new NotFoundGraphError("Graph.target: could not find the \"".concat(edge, "\" edge in the graph."));
      return data.target.key;
    }

    /**
     * Method returning the given edge's extremities.
     *
     * @param  {any}   edge - The edge's key.
     * @return {array}      - The edge's extremities.
     *
     * @throws {Error} - Will throw if the edge isn't in the graph.
     */;
    _proto.extremities = function extremities(edge) {
      edge = '' + edge;
      var edgeData = this._edges.get(edge);
      if (!edgeData) throw new NotFoundGraphError("Graph.extremities: could not find the \"".concat(edge, "\" edge in the graph."));
      return [edgeData.source.key, edgeData.target.key];
    }

    /**
     * Given a node & an edge, returns the other extremity of the edge.
     *
     * @param  {any}   node - The node's key.
     * @param  {any}   edge - The edge's key.
     * @return {any}        - The related node.
     *
     * @throws {Error} - Will throw if the edge isn't in the graph or if the
     *                   edge & node are not related.
     */;
    _proto.opposite = function opposite(node, edge) {
      node = '' + node;
      edge = '' + edge;
      var data = this._edges.get(edge);
      if (!data) throw new NotFoundGraphError("Graph.opposite: could not find the \"".concat(edge, "\" edge in the graph."));
      var source = data.source.key;
      var target = data.target.key;
      if (node === source) return target;
      if (node === target) return source;
      throw new NotFoundGraphError("Graph.opposite: the \"".concat(node, "\" node is not attached to the \"").concat(edge, "\" edge (").concat(source, ", ").concat(target, ")."));
    }

    /**
     * Returns whether the given edge has the given node as extremity.
     *
     * @param  {any}     edge - The edge's key.
     * @param  {any}     node - The node's key.
     * @return {boolean}      - The related node.
     *
     * @throws {Error} - Will throw if either the node or the edge isn't in the graph.
     */;
    _proto.hasExtremity = function hasExtremity(edge, node) {
      edge = '' + edge;
      node = '' + node;
      var data = this._edges.get(edge);
      if (!data) throw new NotFoundGraphError("Graph.hasExtremity: could not find the \"".concat(edge, "\" edge in the graph."));
      return data.source.key === node || data.target.key === node;
    }

    /**
     * Method returning whether the given edge is undirected.
     *
     * @param  {any}     edge - The edge's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the edge isn't in the graph.
     */;
    _proto.isUndirected = function isUndirected(edge) {
      edge = '' + edge;
      var data = this._edges.get(edge);
      if (!data) throw new NotFoundGraphError("Graph.isUndirected: could not find the \"".concat(edge, "\" edge in the graph."));
      return data.undirected;
    }

    /**
     * Method returning whether the given edge is directed.
     *
     * @param  {any}     edge - The edge's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the edge isn't in the graph.
     */;
    _proto.isDirected = function isDirected(edge) {
      edge = '' + edge;
      var data = this._edges.get(edge);
      if (!data) throw new NotFoundGraphError("Graph.isDirected: could not find the \"".concat(edge, "\" edge in the graph."));
      return !data.undirected;
    }

    /**
     * Method returning whether the given edge is a self loop.
     *
     * @param  {any}     edge - The edge's key.
     * @return {boolean}
     *
     * @throws {Error} - Will throw if the edge isn't in the graph.
     */;
    _proto.isSelfLoop = function isSelfLoop(edge) {
      edge = '' + edge;
      var data = this._edges.get(edge);
      if (!data) throw new NotFoundGraphError("Graph.isSelfLoop: could not find the \"".concat(edge, "\" edge in the graph."));
      return data.source === data.target;
    }

    /**---------------------------------------------------------------------------
     * Mutation
     **---------------------------------------------------------------------------
     */

    /**
     * Method used to add a node to the graph.
     *
     * @param  {any}    node         - The node.
     * @param  {object} [attributes] - Optional attributes.
     * @return {any}                 - The node.
     *
     * @throws {Error} - Will throw if the given node already exist.
     * @throws {Error} - Will throw if the given attributes are not an object.
     */;
    _proto.addNode = function addNode(node, attributes) {
      var nodeData = _addNode(this, node, attributes);
      return nodeData.key;
    }

    /**
     * Method used to merge a node into the graph.
     *
     * @param  {any}    node         - The node.
     * @param  {object} [attributes] - Optional attributes.
     * @return {any}                 - The node.
     */;
    _proto.mergeNode = function mergeNode(node, attributes) {
      if (attributes && !isPlainObject(attributes)) throw new InvalidArgumentsGraphError("Graph.mergeNode: invalid attributes. Expecting an object but got \"".concat(attributes, "\""));

      // String coercion
      node = '' + node;
      attributes = attributes || {};

      // If the node already exists, we merge the attributes
      var data = this._nodes.get(node);
      if (data) {
        if (attributes) {
          assign(data.attributes, attributes);
          this.emit('nodeAttributesUpdated', {
            type: 'merge',
            key: node,
            attributes: data.attributes,
            data: attributes
          });
        }
        return [node, false];
      }
      data = new this.NodeDataClass(node, attributes);

      // Adding the node to internal register
      this._nodes.set(node, data);

      // Emitting
      this.emit('nodeAdded', {
        key: node,
        attributes: attributes
      });
      return [node, true];
    }

    /**
     * Method used to add a node if it does not exist in the graph or else to
     * update its attributes using a function.
     *
     * @param  {any}      node      - The node.
     * @param  {function} [updater] - Optional updater function.
     * @return {any}                - The node.
     */;
    _proto.updateNode = function updateNode(node, updater) {
      if (updater && typeof updater !== 'function') throw new InvalidArgumentsGraphError("Graph.updateNode: invalid updater function. Expecting a function but got \"".concat(updater, "\""));

      // String coercion
      node = '' + node;

      // If the node already exists, we update the attributes
      var data = this._nodes.get(node);
      if (data) {
        if (updater) {
          var oldAttributes = data.attributes;
          data.attributes = updater(oldAttributes);
          this.emit('nodeAttributesUpdated', {
            type: 'replace',
            key: node,
            attributes: data.attributes
          });
        }
        return [node, false];
      }
      var attributes = updater ? updater({}) : {};
      data = new this.NodeDataClass(node, attributes);

      // Adding the node to internal register
      this._nodes.set(node, data);

      // Emitting
      this.emit('nodeAdded', {
        key: node,
        attributes: attributes
      });
      return [node, true];
    }

    /**
     * Method used to drop a single node & all its attached edges from the graph.
     *
     * @param  {any}    node - The node.
     * @return {Graph}
     *
     * @throws {Error} - Will throw if the node doesn't exist.
     */;
    _proto.dropNode = function dropNode(node) {
      node = '' + node;
      var nodeData = this._nodes.get(node);
      if (!nodeData) throw new NotFoundGraphError("Graph.dropNode: could not find the \"".concat(node, "\" node in the graph."));
      var edgeData;

      // Removing attached edges
      // NOTE: we could be faster here, but this is such a pain to maintain
      if (this.type !== 'undirected') {
        for (var neighbor in nodeData.out) {
          edgeData = nodeData.out[neighbor];
          do {
            dropEdgeFromData(this, edgeData);
            edgeData = edgeData.next;
          } while (edgeData);
        }
        for (var _neighbor in nodeData["in"]) {
          edgeData = nodeData["in"][_neighbor];
          do {
            dropEdgeFromData(this, edgeData);
            edgeData = edgeData.next;
          } while (edgeData);
        }
      }
      if (this.type !== 'directed') {
        for (var _neighbor2 in nodeData.undirected) {
          edgeData = nodeData.undirected[_neighbor2];
          do {
            dropEdgeFromData(this, edgeData);
            edgeData = edgeData.next;
          } while (edgeData);
        }
      }

      // Dropping the node from the register
      this._nodes["delete"](node);

      // Emitting
      this.emit('nodeDropped', {
        key: node,
        attributes: nodeData.attributes
      });
    }

    /**
     * Method used to drop a single edge from the graph.
     *
     * Arity 1:
     * @param  {any}    edge - The edge.
     *
     * Arity 2:
     * @param  {any}    source - Source node.
     * @param  {any}    target - Target node.
     *
     * @return {Graph}
     *
     * @throws {Error} - Will throw if the edge doesn't exist.
     */;
    _proto.dropEdge = function dropEdge(edge) {
      var edgeData;
      if (arguments.length > 1) {
        var source = '' + arguments[0];
        var target = '' + arguments[1];
        edgeData = getMatchingEdge(this, source, target, this.type);
        if (!edgeData) throw new NotFoundGraphError("Graph.dropEdge: could not find the \"".concat(source, "\" -> \"").concat(target, "\" edge in the graph."));
      } else {
        edge = '' + edge;
        edgeData = this._edges.get(edge);
        if (!edgeData) throw new NotFoundGraphError("Graph.dropEdge: could not find the \"".concat(edge, "\" edge in the graph."));
      }
      dropEdgeFromData(this, edgeData);
      return this;
    }

    /**
     * Method used to drop a single directed edge from the graph.
     *
     * @param  {any}    source - Source node.
     * @param  {any}    target - Target node.
     *
     * @return {Graph}
     *
     * @throws {Error} - Will throw if the edge doesn't exist.
     */;
    _proto.dropDirectedEdge = function dropDirectedEdge(source, target) {
      if (arguments.length < 2) throw new UsageGraphError('Graph.dropDirectedEdge: it does not make sense to try and drop a directed edge by key. What if the edge with this key is undirected? Use #.dropEdge for this purpose instead.');
      if (this.multi) throw new UsageGraphError('Graph.dropDirectedEdge: cannot use a {source,target} combo when dropping an edge in a MultiGraph since we cannot infer the one you want to delete as there could be multiple ones.');
      source = '' + source;
      target = '' + target;
      var edgeData = getMatchingEdge(this, source, target, 'directed');
      if (!edgeData) throw new NotFoundGraphError("Graph.dropDirectedEdge: could not find a \"".concat(source, "\" -> \"").concat(target, "\" edge in the graph."));
      dropEdgeFromData(this, edgeData);
      return this;
    }

    /**
     * Method used to drop a single undirected edge from the graph.
     *
     * @param  {any}    source - Source node.
     * @param  {any}    target - Target node.
     *
     * @return {Graph}
     *
     * @throws {Error} - Will throw if the edge doesn't exist.
     */;
    _proto.dropUndirectedEdge = function dropUndirectedEdge(source, target) {
      if (arguments.length < 2) throw new UsageGraphError('Graph.dropUndirectedEdge: it does not make sense to drop a directed edge by key. What if the edge with this key is undirected? Use #.dropEdge for this purpose instead.');
      if (this.multi) throw new UsageGraphError('Graph.dropUndirectedEdge: cannot use a {source,target} combo when dropping an edge in a MultiGraph since we cannot infer the one you want to delete as there could be multiple ones.');
      var edgeData = getMatchingEdge(this, source, target, 'undirected');
      if (!edgeData) throw new NotFoundGraphError("Graph.dropUndirectedEdge: could not find a \"".concat(source, "\" -> \"").concat(target, "\" edge in the graph."));
      dropEdgeFromData(this, edgeData);
      return this;
    }

    /**
     * Method used to remove every edge & every node from the graph.
     *
     * @return {Graph}
     */;
    _proto.clear = function clear() {
      // Clearing edges
      this._edges.clear();

      // Clearing nodes
      this._nodes.clear();

      // Reset counters
      this._resetInstanceCounters();

      // Emitting
      this.emit('cleared');
    }

    /**
     * Method used to remove every edge from the graph.
     *
     * @return {Graph}
     */;
    _proto.clearEdges = function clearEdges() {
      // Clearing structure index
      var iterator = this._nodes.values();
      var step;
      while (step = iterator.next(), step.done !== true) {
        step.value.clear();
      }

      // Clearing edges
      this._edges.clear();

      // Reset counters
      this._resetInstanceCounters();

      // Emitting
      this.emit('edgesCleared');
    }

    /**---------------------------------------------------------------------------
     * Attributes-related methods
     **---------------------------------------------------------------------------
     */

    /**
     * Method returning the desired graph's attribute.
     *
     * @param  {string} name - Name of the attribute.
     * @return {any}
     */;
    _proto.getAttribute = function getAttribute(name) {
      return this._attributes[name];
    }

    /**
     * Method returning the graph's attributes.
     *
     * @return {object}
     */;
    _proto.getAttributes = function getAttributes() {
      return this._attributes;
    }

    /**
     * Method returning whether the graph has the desired attribute.
     *
     * @param  {string}  name - Name of the attribute.
     * @return {boolean}
     */;
    _proto.hasAttribute = function hasAttribute(name) {
      return this._attributes.hasOwnProperty(name);
    }

    /**
     * Method setting a value for the desired graph's attribute.
     *
     * @param  {string}  name  - Name of the attribute.
     * @param  {any}     value - Value for the attribute.
     * @return {Graph}
     */;
    _proto.setAttribute = function setAttribute(name, value) {
      this._attributes[name] = value;

      // Emitting
      this.emit('attributesUpdated', {
        type: 'set',
        attributes: this._attributes,
        name: name
      });
      return this;
    }

    /**
     * Method using a function to update the desired graph's attribute's value.
     *
     * @param  {string}   name    - Name of the attribute.
     * @param  {function} updater - Function use to update the attribute's value.
     * @return {Graph}
     */;
    _proto.updateAttribute = function updateAttribute(name, updater) {
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError('Graph.updateAttribute: updater should be a function.');
      var value = this._attributes[name];
      this._attributes[name] = updater(value);

      // Emitting
      this.emit('attributesUpdated', {
        type: 'set',
        attributes: this._attributes,
        name: name
      });
      return this;
    }

    /**
     * Method removing the desired graph's attribute.
     *
     * @param  {string} name  - Name of the attribute.
     * @return {Graph}
     */;
    _proto.removeAttribute = function removeAttribute(name) {
      delete this._attributes[name];

      // Emitting
      this.emit('attributesUpdated', {
        type: 'remove',
        attributes: this._attributes,
        name: name
      });
      return this;
    }

    /**
     * Method replacing the graph's attributes.
     *
     * @param  {object} attributes - New attributes.
     * @return {Graph}
     *
     * @throws {Error} - Will throw if given attributes are not a plain object.
     */;
    _proto.replaceAttributes = function replaceAttributes(attributes) {
      if (!isPlainObject(attributes)) throw new InvalidArgumentsGraphError('Graph.replaceAttributes: provided attributes are not a plain object.');
      this._attributes = attributes;

      // Emitting
      this.emit('attributesUpdated', {
        type: 'replace',
        attributes: this._attributes
      });
      return this;
    }

    /**
     * Method merging the graph's attributes.
     *
     * @param  {object} attributes - Attributes to merge.
     * @return {Graph}
     *
     * @throws {Error} - Will throw if given attributes are not a plain object.
     */;
    _proto.mergeAttributes = function mergeAttributes(attributes) {
      if (!isPlainObject(attributes)) throw new InvalidArgumentsGraphError('Graph.mergeAttributes: provided attributes are not a plain object.');
      assign(this._attributes, attributes);

      // Emitting
      this.emit('attributesUpdated', {
        type: 'merge',
        attributes: this._attributes,
        data: attributes
      });
      return this;
    }

    /**
     * Method updating the graph's attributes.
     *
     * @param  {function} updater - Function used to update the attributes.
     * @return {Graph}
     *
     * @throws {Error} - Will throw if given updater is not a function.
     */;
    _proto.updateAttributes = function updateAttributes(updater) {
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError('Graph.updateAttributes: provided updater is not a function.');
      this._attributes = updater(this._attributes);

      // Emitting
      this.emit('attributesUpdated', {
        type: 'update',
        attributes: this._attributes
      });
      return this;
    }

    /**
     * Method used to update each node's attributes using the given function.
     *
     * @param {function}  updater - Updater function to use.
     * @param {object}    [hints] - Optional hints.
     */;
    _proto.updateEachNodeAttributes = function updateEachNodeAttributes(updater, hints) {
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError('Graph.updateEachNodeAttributes: expecting an updater function.');
      if (hints && !validateHints(hints)) throw new InvalidArgumentsGraphError('Graph.updateEachNodeAttributes: invalid hints. Expecting an object having the following shape: {attributes?: [string]}');
      var iterator = this._nodes.values();
      var step, nodeData;
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        nodeData.attributes = updater(nodeData.key, nodeData.attributes);
      }
      this.emit('eachNodeAttributesUpdated', {
        hints: hints ? hints : null
      });
    }

    /**
     * Method used to update each edge's attributes using the given function.
     *
     * @param {function}  updater - Updater function to use.
     * @param {object}    [hints] - Optional hints.
     */;
    _proto.updateEachEdgeAttributes = function updateEachEdgeAttributes(updater, hints) {
      if (typeof updater !== 'function') throw new InvalidArgumentsGraphError('Graph.updateEachEdgeAttributes: expecting an updater function.');
      if (hints && !validateHints(hints)) throw new InvalidArgumentsGraphError('Graph.updateEachEdgeAttributes: invalid hints. Expecting an object having the following shape: {attributes?: [string]}');
      var iterator = this._edges.values();
      var step, edgeData, sourceData, targetData;
      while (step = iterator.next(), step.done !== true) {
        edgeData = step.value;
        sourceData = edgeData.source;
        targetData = edgeData.target;
        edgeData.attributes = updater(edgeData.key, edgeData.attributes, sourceData.key, targetData.key, sourceData.attributes, targetData.attributes, edgeData.undirected);
      }
      this.emit('eachEdgeAttributesUpdated', {
        hints: hints ? hints : null
      });
    }

    /**---------------------------------------------------------------------------
     * Iteration-related methods
     **---------------------------------------------------------------------------
     */

    /**
     * Method iterating over the graph's adjacency using the given callback.
     *
     * @param  {function}  callback - Callback to use.
     */;
    _proto.forEachAdjacencyEntry = function forEachAdjacencyEntry(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.forEachAdjacencyEntry: expecting a callback.');
      forEachAdjacency(false, false, false, this, callback);
    };
    _proto.forEachAdjacencyEntryWithOrphans = function forEachAdjacencyEntryWithOrphans(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.forEachAdjacencyEntryWithOrphans: expecting a callback.');
      forEachAdjacency(false, false, true, this, callback);
    }

    /**
     * Method iterating over the graph's assymetric adjacency using the given callback.
     *
     * @param  {function}  callback - Callback to use.
     */;
    _proto.forEachAssymetricAdjacencyEntry = function forEachAssymetricAdjacencyEntry(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.forEachAssymetricAdjacencyEntry: expecting a callback.');
      forEachAdjacency(false, true, false, this, callback);
    };
    _proto.forEachAssymetricAdjacencyEntryWithOrphans = function forEachAssymetricAdjacencyEntryWithOrphans(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.forEachAssymetricAdjacencyEntryWithOrphans: expecting a callback.');
      forEachAdjacency(false, true, true, this, callback);
    }

    /**
     * Method returning the list of the graph's nodes.
     *
     * @return {array} - The nodes.
     */;
    _proto.nodes = function nodes() {
      return Array.from(this._nodes.keys());
    }

    /**
     * Method iterating over the graph's nodes using the given callback.
     *
     * @param  {function}  callback - Callback (key, attributes, index).
     */;
    _proto.forEachNode = function forEachNode(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.forEachNode: expecting a callback.');
      var iterator = this._nodes.values();
      var step, nodeData;
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        callback(nodeData.key, nodeData.attributes);
      }
    }

    /**
     * Method iterating attempting to find a node matching the given predicate
     * function.
     *
     * @param  {function}  callback - Callback (key, attributes).
     */;
    _proto.findNode = function findNode(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.findNode: expecting a callback.');
      var iterator = this._nodes.values();
      var step, nodeData;
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        if (callback(nodeData.key, nodeData.attributes)) return nodeData.key;
      }
      return;
    }

    /**
     * Method mapping nodes.
     *
     * @param  {function}  callback - Callback (key, attributes).
     */;
    _proto.mapNodes = function mapNodes(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.mapNode: expecting a callback.');
      var iterator = this._nodes.values();
      var step, nodeData;
      var result = new Array(this.order);
      var i = 0;
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        result[i++] = callback(nodeData.key, nodeData.attributes);
      }
      return result;
    }

    /**
     * Method returning whether some node verify the given predicate.
     *
     * @param  {function}  callback - Callback (key, attributes).
     */;
    _proto.someNode = function someNode(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.someNode: expecting a callback.');
      var iterator = this._nodes.values();
      var step, nodeData;
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        if (callback(nodeData.key, nodeData.attributes)) return true;
      }
      return false;
    }

    /**
     * Method returning whether all node verify the given predicate.
     *
     * @param  {function}  callback - Callback (key, attributes).
     */;
    _proto.everyNode = function everyNode(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.everyNode: expecting a callback.');
      var iterator = this._nodes.values();
      var step, nodeData;
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        if (!callback(nodeData.key, nodeData.attributes)) return false;
      }
      return true;
    }

    /**
     * Method filtering nodes.
     *
     * @param  {function}  callback - Callback (key, attributes).
     */;
    _proto.filterNodes = function filterNodes(callback) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.filterNodes: expecting a callback.');
      var iterator = this._nodes.values();
      var step, nodeData;
      var result = [];
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        if (callback(nodeData.key, nodeData.attributes)) result.push(nodeData.key);
      }
      return result;
    }

    /**
     * Method reducing nodes.
     *
     * @param  {function}  callback - Callback (accumulator, key, attributes).
     */;
    _proto.reduceNodes = function reduceNodes(callback, initialValue) {
      if (typeof callback !== 'function') throw new InvalidArgumentsGraphError('Graph.reduceNodes: expecting a callback.');
      if (arguments.length < 2) throw new InvalidArgumentsGraphError('Graph.reduceNodes: missing initial value. You must provide it because the callback takes more than one argument and we cannot infer the initial value from the first iteration, as you could with a simple array.');
      var accumulator = initialValue;
      var iterator = this._nodes.values();
      var step, nodeData;
      while (step = iterator.next(), step.done !== true) {
        nodeData = step.value;
        accumulator = callback(accumulator, nodeData.key, nodeData.attributes);
      }
      return accumulator;
    }

    /**
     * Method returning an iterator over the graph's node entries.
     *
     * @return {Iterator}
     */;
    _proto.nodeEntries = function nodeEntries() {
      var iterator = this._nodes.values();
      return _defineProperty(_defineProperty({}, Symbol.iterator, function () {
        return this;
      }), "next", function next() {
        var step = iterator.next();
        if (step.done) return step;
        var data = step.value;
        return {
          value: {
            node: data.key,
            attributes: data.attributes
          },
          done: false
        };
      });
    }

    /**---------------------------------------------------------------------------
     * Serialization
     **---------------------------------------------------------------------------
     */

    /**
     * Method used to export the whole graph.
     *
     * @return {object} - The serialized graph.
     */;
    _proto["export"] = function _export() {
      var _this2 = this;
      var nodes = new Array(this._nodes.size);
      var i = 0;
      this._nodes.forEach(function (data, key) {
        nodes[i++] = serializeNode(key, data);
      });
      var edges = new Array(this._edges.size);
      i = 0;
      this._edges.forEach(function (data, key) {
        edges[i++] = serializeEdge(_this2.type, key, data);
      });
      return {
        options: {
          type: this.type,
          multi: this.multi,
          allowSelfLoops: this.allowSelfLoops
        },
        attributes: this.getAttributes(),
        nodes: nodes,
        edges: edges
      };
    }

    /**
     * Method used to import a serialized graph.
     *
     * @param  {object|Graph} data  - The serialized graph.
     * @param  {boolean}      merge - Whether to merge data.
     * @return {Graph}              - Returns itself for chaining.
     */;
    _proto["import"] = function _import(data) {
      var _this3 = this;
      var merge = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : false;
      // Importing a Graph instance directly
      if (data instanceof Graph) {
        // Nodes
        data.forEachNode(function (n, a) {
          if (merge) _this3.mergeNode(n, a);else _this3.addNode(n, a);
        });

        // Edges
        data.forEachEdge(function (e, a, s, t, _sa, _ta, u) {
          if (merge) {
            if (u) _this3.mergeUndirectedEdgeWithKey(e, s, t, a);else _this3.mergeDirectedEdgeWithKey(e, s, t, a);
          } else {
            if (u) _this3.addUndirectedEdgeWithKey(e, s, t, a);else _this3.addDirectedEdgeWithKey(e, s, t, a);
          }
        });
        return this;
      }

      // Importing a serialized graph
      if (!isPlainObject(data)) throw new InvalidArgumentsGraphError('Graph.import: invalid argument. Expecting a serialized graph or, alternatively, a Graph instance.');
      if (data.attributes) {
        if (!isPlainObject(data.attributes)) throw new InvalidArgumentsGraphError('Graph.import: invalid attributes. Expecting a plain object.');
        if (merge) this.mergeAttributes(data.attributes);else this.replaceAttributes(data.attributes);
      }
      var i, l, list, node, edge;
      if (data.nodes) {
        list = data.nodes;
        if (!Array.isArray(list)) throw new InvalidArgumentsGraphError('Graph.import: invalid nodes. Expecting an array.');
        for (i = 0, l = list.length; i < l; i++) {
          node = list[i];

          // Validating
          validateSerializedNode(node);

          // Adding the node
          var _node = node,
            key = _node.key,
            attributes = _node.attributes;
          if (merge) this.mergeNode(key, attributes);else this.addNode(key, attributes);
        }
      }
      if (data.edges) {
        var undirectedByDefault = false;
        if (this.type === 'undirected') {
          undirectedByDefault = true;
        }
        list = data.edges;
        if (!Array.isArray(list)) throw new InvalidArgumentsGraphError('Graph.import: invalid edges. Expecting an array.');
        for (i = 0, l = list.length; i < l; i++) {
          edge = list[i];

          // Validating
          validateSerializedEdge(edge);

          // Adding the edge
          var _edge = edge,
            source = _edge.source,
            target = _edge.target,
            _attributes = _edge.attributes,
            _edge$undirected = _edge.undirected,
            undirected = _edge$undirected === void 0 ? undirectedByDefault : _edge$undirected;
          var method = void 0;
          if ('key' in edge) {
            method = merge ? undirected ? this.mergeUndirectedEdgeWithKey : this.mergeDirectedEdgeWithKey : undirected ? this.addUndirectedEdgeWithKey : this.addDirectedEdgeWithKey;
            method.call(this, edge.key, source, target, _attributes);
          } else {
            method = merge ? undirected ? this.mergeUndirectedEdge : this.mergeDirectedEdge : undirected ? this.addUndirectedEdge : this.addDirectedEdge;
            method.call(this, source, target, _attributes);
          }
        }
      }
      return this;
    }

    /**---------------------------------------------------------------------------
     * Utils
     **---------------------------------------------------------------------------
     */

    /**
     * Method returning a null copy of the graph, i.e. a graph without nodes
     * & edges but with the exact same options.
     *
     * @param  {object} options - Options to merge with the current ones.
     * @return {Graph}          - The null copy.
     */;
    _proto.nullCopy = function nullCopy(options) {
      var graph = new Graph(assign({}, this._options, options));
      graph.replaceAttributes(assign({}, this.getAttributes()));
      return graph;
    }

    /**
     * Method returning an empty copy of the graph, i.e. a graph without edges but
     * with the exact same options.
     *
     * @param  {object} options - Options to merge with the current ones.
     * @return {Graph}          - The empty copy.
     */;
    _proto.emptyCopy = function emptyCopy(options) {
      var graph = this.nullCopy(options);
      this._nodes.forEach(function (nodeData, key) {
        var attributes = assign({}, nodeData.attributes);

        // NOTE: no need to emit events since user cannot access the instance yet
        nodeData = new graph.NodeDataClass(key, attributes);
        graph._nodes.set(key, nodeData);
      });
      return graph;
    }

    /**
     * Method returning an exact copy of the graph.
     *
     * @param  {object} options - Upgrade options.
     * @return {Graph}          - The copy.
     */;
    _proto.copy = function copy(options) {
      options = options || {};
      if (typeof options.type === 'string' && options.type !== this.type && options.type !== 'mixed') throw new UsageGraphError("Graph.copy: cannot create an incompatible copy from \"".concat(this.type, "\" type to \"").concat(options.type, "\" because this would mean losing information about the current graph."));
      if (typeof options.multi === 'boolean' && options.multi !== this.multi && options.multi !== true) throw new UsageGraphError('Graph.copy: cannot create an incompatible copy by downgrading a multi graph to a simple one because this would mean losing information about the current graph.');
      if (typeof options.allowSelfLoops === 'boolean' && options.allowSelfLoops !== this.allowSelfLoops && options.allowSelfLoops !== true) throw new UsageGraphError('Graph.copy: cannot create an incompatible copy from a graph allowing self loops to one that does not because this would mean losing information about the current graph.');
      var graph = this.emptyCopy(options);
      var iterator = this._edges.values();
      var step, edgeData;
      while (step = iterator.next(), step.done !== true) {
        edgeData = step.value;

        // NOTE: no need to emit events since user cannot access the instance yet
        addEdge(graph, 'copy', false, edgeData.undirected, edgeData.key, edgeData.source.key, edgeData.target.key, assign({}, edgeData.attributes));
      }
      return graph;
    }

    /**---------------------------------------------------------------------------
     * Known methods
     **---------------------------------------------------------------------------
     */

    /**
     * Method used by JavaScript to perform JSON serialization.
     *
     * @return {object} - The serialized graph.
     */;
    _proto.toJSON = function toJSON() {
      return this["export"]();
    }

    /**
     * Method returning [object Graph].
     */;
    _proto.toString = function toString() {
      return '[object Graph]';
    }

    /**
     * Method used internally by node's console to display a custom object.
     *
     * @return {object} - Formatted object representation of the graph.
     */;
    _proto.inspect = function inspect() {
      var _this4 = this;
      var nodes = {};
      this._nodes.forEach(function (data, key) {
        nodes[key] = data.attributes;
      });
      var edges = {},
        multiIndex = {};
      this._edges.forEach(function (data, key) {
        var direction = data.undirected ? '--' : '->';
        var label = '';
        var source = data.source.key;
        var target = data.target.key;
        var tmp;
        if (data.undirected && source > target) {
          tmp = source;
          source = target;
          target = tmp;
        }
        var desc = "(".concat(source, ")").concat(direction, "(").concat(target, ")");
        if (!key.startsWith('geid_')) {
          label += "[".concat(key, "]: ");
        } else if (_this4.multi) {
          if (typeof multiIndex[desc] === 'undefined') {
            multiIndex[desc] = 0;
          } else {
            multiIndex[desc]++;
          }
          label += "".concat(multiIndex[desc], ". ");
        }
        label += desc;
        edges[label] = data.attributes;
      });
      var dummy = {};
      for (var k in this) {
        if (this.hasOwnProperty(k) && !EMITTER_PROPS.has(k) && typeof this[k] !== 'function' && _typeof(k) !== 'symbol') dummy[k] = this[k];
      }
      dummy.attributes = this._attributes;
      dummy.nodes = nodes;
      dummy.edges = edges;
      privateProperty(dummy, 'constructor', this.constructor);
      return dummy;
    };
    return Graph;
  }(events.exports.EventEmitter);
  if (typeof Symbol !== 'undefined') Graph.prototype[Symbol["for"]('nodejs.util.inspect.custom')] = Graph.prototype.inspect;

  /**
   * Related to edge addition.
   */
  EDGE_ADD_METHODS.forEach(function (method) {
    ['add', 'merge', 'update'].forEach(function (verb) {
      var name = method.name(verb);
      var fn = verb === 'add' ? addEdge : mergeEdge;
      if (method.generateKey) {
        Graph.prototype[name] = function (source, target, attributes) {
          return fn(this, name, true, (method.type || this.type) === 'undirected', null, source, target, attributes, verb === 'update');
        };
      } else {
        Graph.prototype[name] = function (edge, source, target, attributes) {
          return fn(this, name, false, (method.type || this.type) === 'undirected', edge, source, target, attributes, verb === 'update');
        };
      }
    });
  });

  /**
   * Attributes-related.
   */
  attachNodeAttributesMethods(Graph);
  attachEdgeAttributesMethods(Graph);

  /**
   * Edge iteration-related.
   */
  attachEdgeIterationMethods(Graph);

  /**
   * Neighbor iteration-related.
   */
  attachNeighborIterationMethods(Graph);

  /**
   * Alternative constructors.
   */
  var DirectedGraph = /*#__PURE__*/function (_Graph) {
    _inheritsLoose(DirectedGraph, _Graph);
    function DirectedGraph(options) {
      var finalOptions = assign({
        type: 'directed'
      }, options);
      if ('multi' in finalOptions && finalOptions.multi !== false) throw new InvalidArgumentsGraphError('DirectedGraph.from: inconsistent indication that the graph should be multi in given options!');
      if (finalOptions.type !== 'directed') throw new InvalidArgumentsGraphError('DirectedGraph.from: inconsistent "' + finalOptions.type + '" type in given options!');
      return _Graph.call(this, finalOptions) || this;
    }
    return DirectedGraph;
  }(Graph);
  var UndirectedGraph = /*#__PURE__*/function (_Graph2) {
    _inheritsLoose(UndirectedGraph, _Graph2);
    function UndirectedGraph(options) {
      var finalOptions = assign({
        type: 'undirected'
      }, options);
      if ('multi' in finalOptions && finalOptions.multi !== false) throw new InvalidArgumentsGraphError('UndirectedGraph.from: inconsistent indication that the graph should be multi in given options!');
      if (finalOptions.type !== 'undirected') throw new InvalidArgumentsGraphError('UndirectedGraph.from: inconsistent "' + finalOptions.type + '" type in given options!');
      return _Graph2.call(this, finalOptions) || this;
    }
    return UndirectedGraph;
  }(Graph);
  var MultiGraph = /*#__PURE__*/function (_Graph3) {
    _inheritsLoose(MultiGraph, _Graph3);
    function MultiGraph(options) {
      var finalOptions = assign({
        multi: true
      }, options);
      if ('multi' in finalOptions && finalOptions.multi !== true) throw new InvalidArgumentsGraphError('MultiGraph.from: inconsistent indication that the graph should be simple in given options!');
      return _Graph3.call(this, finalOptions) || this;
    }
    return MultiGraph;
  }(Graph);
  var MultiDirectedGraph = /*#__PURE__*/function (_Graph4) {
    _inheritsLoose(MultiDirectedGraph, _Graph4);
    function MultiDirectedGraph(options) {
      var finalOptions = assign({
        type: 'directed',
        multi: true
      }, options);
      if ('multi' in finalOptions && finalOptions.multi !== true) throw new InvalidArgumentsGraphError('MultiDirectedGraph.from: inconsistent indication that the graph should be simple in given options!');
      if (finalOptions.type !== 'directed') throw new InvalidArgumentsGraphError('MultiDirectedGraph.from: inconsistent "' + finalOptions.type + '" type in given options!');
      return _Graph4.call(this, finalOptions) || this;
    }
    return MultiDirectedGraph;
  }(Graph);
  var MultiUndirectedGraph = /*#__PURE__*/function (_Graph5) {
    _inheritsLoose(MultiUndirectedGraph, _Graph5);
    function MultiUndirectedGraph(options) {
      var finalOptions = assign({
        type: 'undirected',
        multi: true
      }, options);
      if ('multi' in finalOptions && finalOptions.multi !== true) throw new InvalidArgumentsGraphError('MultiUndirectedGraph.from: inconsistent indication that the graph should be simple in given options!');
      if (finalOptions.type !== 'undirected') throw new InvalidArgumentsGraphError('MultiUndirectedGraph.from: inconsistent "' + finalOptions.type + '" type in given options!');
      return _Graph5.call(this, finalOptions) || this;
    }
    return MultiUndirectedGraph;
  }(Graph);
  /**
   * Attaching static #.from method to each of the constructors.
   */
  function attachStaticFromMethod(Class) {
    /**
     * Builds a graph from serialized data or another graph's data.
     *
     * @param  {Graph|SerializedGraph} data      - Hydratation data.
     * @param  {object}                [options] - Options.
     * @return {Class}
     */
    Class.from = function (data, options) {
      // Merging given options with serialized ones
      var finalOptions = assign({}, data.options, options);
      var instance = new Class(finalOptions);
      instance["import"](data);
      return instance;
    };
  }
  attachStaticFromMethod(Graph);
  attachStaticFromMethod(DirectedGraph);
  attachStaticFromMethod(UndirectedGraph);
  attachStaticFromMethod(MultiGraph);
  attachStaticFromMethod(MultiDirectedGraph);
  attachStaticFromMethod(MultiUndirectedGraph);
  Graph.Graph = Graph;
  Graph.DirectedGraph = DirectedGraph;
  Graph.UndirectedGraph = UndirectedGraph;
  Graph.MultiGraph = MultiGraph;
  Graph.MultiDirectedGraph = MultiDirectedGraph;
  Graph.MultiUndirectedGraph = MultiUndirectedGraph;
  Graph.InvalidArgumentsGraphError = InvalidArgumentsGraphError;
  Graph.NotFoundGraphError = NotFoundGraphError;
  Graph.UsageGraphError = UsageGraphError;

  /**
   * Graphology CommonJS Endoint
   * ============================
   *
   * Endpoint for CommonJS modules consumers.
   */

  return Graph;

}));
//# sourceMappingURL=graphology.umd.js.map