index.js

var MutationObserver = window.MutationObserver
  || window.WebKitMutationObserver
  || window.MozMutationObserver;

/*
 * Copyright 2012 The Polymer Authors. All rights reserved.
 * Use of this source code is goverened by a BSD-style
 * license that can be found in the LICENSE file.
 */

var WeakMap = window.WeakMap;

if (typeof WeakMap === 'undefined') {
  var defineProperty = Object.defineProperty;
  var counter = Date.now() % 1e9;

  WeakMap = function() {
    this.name = '__st' + (Math.random() * 1e9 >>> 0) + (counter++ + '__');
  };

  WeakMap.prototype = {
    set: function(key, value) {
      var entry = key[this.name];
      if (entry && entry[0] === key)
        entry[1] = value;
      else
        defineProperty(key, this.name, {value: [key, value], writable: true});
      return this;
    },
    get: function(key) {
      var entry;
      return (entry = key[this.name]) && entry[0] === key ?
          entry[1] : undefined;
    },
    'delete': function(key) {
      var entry = key[this.name];
      if (!entry) return false;
      var hasValue = entry[0] === key;
      entry[0] = entry[1] = undefined;
      return hasValue;
    },
    has: function(key) {
      var entry = key[this.name];
      if (!entry) return false;
      return entry[0] === key;
    }
  };
}

var registrationsTable = new WeakMap();

// We use setImmediate or postMessage for our future callback.
var setImmediate = window.msSetImmediate;

// Use post message to emulate setImmediate.
if (!setImmediate) {
  var setImmediateQueue = [];
  var sentinel = String(Math.random());
  window.addEventListener('message', function(e) {
    if (e.data === sentinel) {
      var queue = setImmediateQueue;
      setImmediateQueue = [];
      queue.forEach(function(func) {
        func();
      });
    }
  });
  setImmediate = function(func) {
    setImmediateQueue.push(func);
    window.postMessage(sentinel, '*');
  };
}

// This is used to ensure that we never schedule 2 callas to setImmediate
var isScheduled = false;

// Keep track of observers that needs to be notified next time.
var scheduledObservers = [];

/**
 * Schedules |dispatchCallback| to be called in the future.
 * @param {MutationObserver} observer
 */
function scheduleCallback(observer) {
  scheduledObservers.push(observer);
  if (!isScheduled) {
    isScheduled = true;
    setImmediate(dispatchCallbacks);
  }
}

function wrapIfNeeded(node) {
  return window.ShadowDOMPolyfill &&
      window.ShadowDOMPolyfill.wrapIfNeeded(node) ||
      node;
}

function dispatchCallbacks() {
  // http://dom.spec.whatwg.org/#mutation-observers

  isScheduled = false; // Used to allow a new setImmediate call above.

  var observers = scheduledObservers;
  scheduledObservers = [];
  // Sort observers based on their creation UID (incremental).
  observers.sort(function(o1, o2) {
    return o1.uid_ - o2.uid_;
  });

  var anyNonEmpty = false;
  observers.forEach(function(observer) {

    // 2.1, 2.2
    var queue = observer.takeRecords();
    // 2.3. Remove all transient registered observers whose observer is mo.
    removeTransientObserversFor(observer);

    // 2.4
    if (queue.length) {
      observer.callback_(queue, observer);
      anyNonEmpty = true;
    }
  });

  // 3.
  if (anyNonEmpty)
    dispatchCallbacks();
}

function removeTransientObserversFor(observer) {
  observer.nodes_.forEach(function(node) {
    var registrations = registrationsTable.get(node);
    if (!registrations)
      return;
    registrations.forEach(function(registration) {
      if (registration.observer === observer)
        registration.removeTransientObservers();
    });
  });
}

/**
 * This function is used for the "For each registered observer observer (with
 * observer's options as options) in target's list of registered observers,
 * run these substeps:" and the "For each ancestor ancestor of target, and for
 * each registered observer observer (with options options) in ancestor's list
 * of registered observers, run these substeps:" part of the algorithms. The
 * |options.subtree| is checked to ensure that the callback is called
 * correctly.
 *
 * @param {Node} target
 * @param {function(MutationObserverInit):MutationRecord} callback
 */
function forEachAncestorAndObserverEnqueueRecord(target, callback) {
  for (var node = target; node; node = node.parentNode) {
    var registrations = registrationsTable.get(node);

    if (registrations) {
      for (var j = 0; j < registrations.length; j++) {
        var registration = registrations[j];
        var options = registration.options;

        // Only target ignores subtree.
        if (node !== target && !options.subtree)
          continue;

        var record = callback(options);
        if (record)
          registration.enqueue(record);
      }
    }
  }
}

var uidCounter = 0;

/**
 * The class that maps to the DOM MutationObserver interface.
 * @param {Function} callback.
 * @constructor
 */
function JsMutationObserver(callback) {
  this.callback_ = callback;
  this.nodes_ = [];
  this.records_ = [];
  this.uid_ = ++uidCounter;
}

JsMutationObserver.prototype = {
  observe: function(target, options) {
    target = wrapIfNeeded(target);

    // 1.1
    if (!options.childList && !options.attributes && !options.characterData ||

        // 1.2
        options.attributeOldValue && !options.attributes ||

        // 1.3
        options.attributeFilter && options.attributeFilter.length &&
            !options.attributes ||

        // 1.4
        options.characterDataOldValue && !options.characterData) {

      throw new SyntaxError();
    }

    var registrations = registrationsTable.get(target);
    if (!registrations)
      registrationsTable.set(target, registrations = []);

    // 2
    // If target's list of registered observers already includes a registered
    // observer associated with the context object, replace that registered
    // observer's options with options.
    var registration;
    for (var i = 0; i < registrations.length; i++) {
      if (registrations[i].observer === this) {
        registration = registrations[i];
        registration.removeListeners();
        registration.options = options;
        break;
      }
    }

    // 3.
    // Otherwise, add a new registered observer to target's list of registered
    // observers with the context object as the observer and options as the
    // options, and add target to context object's list of nodes on which it
    // is registered.
    if (!registration) {
      registration = new Registration(this, target, options);
      registrations.push(registration);
      this.nodes_.push(target);
    }

    registration.addListeners();
  },

  disconnect: function() {
    this.nodes_.forEach(function(node) {
      var registrations = registrationsTable.get(node);
      for (var i = 0; i < registrations.length; i++) {
        var registration = registrations[i];
        if (registration.observer === this) {
          registration.removeListeners();
          registrations.splice(i, 1);
          // Each node can only have one registered observer associated with
          // this observer.
          break;
        }
      }
    }, this);
    this.records_ = [];
  },

  takeRecords: function() {
    var copyOfRecords = this.records_;
    this.records_ = [];
    return copyOfRecords;
  }
};

/**
 * @param {string} type
 * @param {Node} target
 * @constructor
 */
function MutationRecord(type, target) {
  this.type = type;
  this.target = target;
  this.addedNodes = [];
  this.removedNodes = [];
  this.previousSibling = null;
  this.nextSibling = null;
  this.attributeName = null;
  this.attributeNamespace = null;
  this.oldValue = null;
}

function copyMutationRecord(original) {
  var record = new MutationRecord(original.type, original.target);
  record.addedNodes = original.addedNodes.slice();
  record.removedNodes = original.removedNodes.slice();
  record.previousSibling = original.previousSibling;
  record.nextSibling = original.nextSibling;
  record.attributeName = original.attributeName;
  record.attributeNamespace = original.attributeNamespace;
  record.oldValue = original.oldValue;
  return record;
};

// We keep track of the two (possibly one) records used in a single mutation.
var currentRecord, recordWithOldValue;

/**
 * Creates a record without |oldValue| and caches it as |currentRecord| for
 * later use.
 * @param {string} oldValue
 * @return {MutationRecord}
 */
function getRecord(type, target) {
  return currentRecord = new MutationRecord(type, target);
}

/**
 * Gets or creates a record with |oldValue| based in the |currentRecord|
 * @param {string} oldValue
 * @return {MutationRecord}
 */
function getRecordWithOldValue(oldValue) {
  if (recordWithOldValue)
    return recordWithOldValue;
  recordWithOldValue = copyMutationRecord(currentRecord);
  recordWithOldValue.oldValue = oldValue;
  return recordWithOldValue;
}

function clearRecords() {
  currentRecord = recordWithOldValue = undefined;
}

/**
 * @param {MutationRecord} record
 * @return {boolean} Whether the record represents a record from the current
 * mutation event.
 */
function recordRepresentsCurrentMutation(record) {
  return record === recordWithOldValue || record === currentRecord;
}

/**
 * Selects which record, if any, to replace the last record in the queue.
 * This returns |null| if no record should be replaced.
 *
 * @param {MutationRecord} lastRecord
 * @param {MutationRecord} newRecord
 * @param {MutationRecord}
 */
function selectRecord(lastRecord, newRecord) {
  if (lastRecord === newRecord)
    return lastRecord;

  // Check if the the record we are adding represents the same record. If
  // so, we keep the one with the oldValue in it.
  if (recordWithOldValue && recordRepresentsCurrentMutation(lastRecord))
    return recordWithOldValue;

  return null;
}

/**
 * Class used to represent a registered observer.
 * @param {MutationObserver} observer
 * @param {Node} target
 * @param {MutationObserverInit} options
 * @constructor
 */
function Registration(observer, target, options) {
  this.observer = observer;
  this.target = target;
  this.options = options;
  this.transientObservedNodes = [];
}

Registration.prototype = {
  enqueue: function(record) {
    var records = this.observer.records_;
    var length = records.length;

    // There are cases where we replace the last record with the new record.
    // For example if the record represents the same mutation we need to use
    // the one with the oldValue. If we get same record (this can happen as we
    // walk up the tree) we ignore the new record.
    if (records.length > 0) {
      var lastRecord = records[length - 1];
      var recordToReplaceLast = selectRecord(lastRecord, record);
      if (recordToReplaceLast) {
        records[length - 1] = recordToReplaceLast;
        return;
      }
    } else {
      scheduleCallback(this.observer);
    }

    records[length] = record;
  },

  addListeners: function() {
    this.addListeners_(this.target);
  },

  addListeners_: function(node) {
    var options = this.options;
    if (options.attributes)
      node.addEventListener('DOMAttrModified', this, true);

    if (options.characterData)
      node.addEventListener('DOMCharacterDataModified', this, true);

    if (options.childList)
      node.addEventListener('DOMNodeInserted', this, true);

    if (options.childList || options.subtree)
      node.addEventListener('DOMNodeRemoved', this, true);
  },

  removeListeners: function() {
    this.removeListeners_(this.target);
  },

  removeListeners_: function(node) {
    var options = this.options;
    if (options.attributes)
      node.removeEventListener('DOMAttrModified', this, true);

    if (options.characterData)
      node.removeEventListener('DOMCharacterDataModified', this, true);

    if (options.childList)
      node.removeEventListener('DOMNodeInserted', this, true);

    if (options.childList || options.subtree)
      node.removeEventListener('DOMNodeRemoved', this, true);
  },

  /**
   * Adds a transient observer on node. The transient observer gets removed
   * next time we deliver the change records.
   * @param {Node} node
   */
  addTransientObserver: function(node) {
    // Don't add transient observers on the target itself. We already have all
    // the required listeners set up on the target.
    if (node === this.target)
      return;

    this.addListeners_(node);
    this.transientObservedNodes.push(node);
    var registrations = registrationsTable.get(node);
    if (!registrations)
      registrationsTable.set(node, registrations = []);

    // We know that registrations does not contain this because we already
    // checked if node === this.target.
    registrations.push(this);
  },

  removeTransientObservers: function() {
    var transientObservedNodes = this.transientObservedNodes;
    this.transientObservedNodes = [];

    transientObservedNodes.forEach(function(node) {
      // Transient observers are never added to the target.
      this.removeListeners_(node);

      var registrations = registrationsTable.get(node);
      for (var i = 0; i < registrations.length; i++) {
        if (registrations[i] === this) {
          registrations.splice(i, 1);
          // Each node can only have one registered observer associated with
          // this observer.
          break;
        }
      }
    }, this);
  },

  handleEvent: function(e) {
    // Stop propagation since we are managing the propagation manually.
    // This means that other mutation events on the page will not work
    // correctly but that is by design.
    e.stopImmediatePropagation();

    switch (e.type) {
      case 'DOMAttrModified':
        // http://dom.spec.whatwg.org/#concept-mo-queue-attributes

        var name = e.attrName;
        var namespace = e.relatedNode.namespaceURI;
        var target = e.target;

        // 1.
        var record = new getRecord('attributes', target);
        record.attributeName = name;
        record.attributeNamespace = namespace;

        // 2.
        var oldValue =
            e.attrChange === MutationEvent.ADDITION ? null : e.prevValue;

        forEachAncestorAndObserverEnqueueRecord(target, function(options) {
          // 3.1, 4.2
          if (!options.attributes)
            return;

          // 3.2, 4.3
          if (options.attributeFilter && options.attributeFilter.length &&
              options.attributeFilter.indexOf(name) === -1 &&
              options.attributeFilter.indexOf(namespace) === -1) {
            return;
          }
          // 3.3, 4.4
          if (options.attributeOldValue)
            return getRecordWithOldValue(oldValue);

          // 3.4, 4.5
          return record;
        });

        break;

      case 'DOMCharacterDataModified':
        // http://dom.spec.whatwg.org/#concept-mo-queue-characterdata
        var target = e.target;

        // 1.
        var record = getRecord('characterData', target);

        // 2.
        var oldValue = e.prevValue;


        forEachAncestorAndObserverEnqueueRecord(target, function(options) {
          // 3.1, 4.2
          if (!options.characterData)
            return;

          // 3.2, 4.3
          if (options.characterDataOldValue)
            return getRecordWithOldValue(oldValue);

          // 3.3, 4.4
          return record;
        });

        break;

      case 'DOMNodeRemoved':
        this.addTransientObserver(e.target);
        // Fall through.
      case 'DOMNodeInserted':
        // http://dom.spec.whatwg.org/#concept-mo-queue-childlist
        var target = e.relatedNode;
        var changedNode = e.target;
        var addedNodes, removedNodes;
        if (e.type === 'DOMNodeInserted') {
          addedNodes = [changedNode];
          removedNodes = [];
        } else {

          addedNodes = [];
          removedNodes = [changedNode];
        }
        var previousSibling = changedNode.previousSibling;
        var nextSibling = changedNode.nextSibling;

        // 1.
        var record = getRecord('childList', target);
        record.addedNodes = addedNodes;
        record.removedNodes = removedNodes;
        record.previousSibling = previousSibling;
        record.nextSibling = nextSibling;

        forEachAncestorAndObserverEnqueueRecord(target, function(options) {
          // 2.1, 3.2
          if (!options.childList)
            return;

          // 2.2, 3.3
          return record;
        });

    }

    clearRecords();
  }
};

if (!MutationObserver) {
  MutationObserver = JsMutationObserver;
}

module.exports = MutationObserver;