diffList.js

define(['angular'], function(angular) {
    
    // add a few helpers
    Array.prototype.union = function(a){
        var r = this.slice(0);
        a.forEach(function(i) { if (r.indexOf(i) < 0) r.push(i); });
        return r;
    };

    Array.prototype.diff = function(a){
        return this.filter(function(i) {return a.indexOf(i) < 0;});
    };

    // Inspired from: https://gist.github.com/katowulf/6193808
    var module = angular.module('utils.diff', []);

    /**
     * A diff utility that compares arrays and returns a list of added, removed, and updated items
     *
     * Returns an object with two methods:
     *    diff:  do a one-time diff of two arrays
     *    watch: observe a variable on scope and report any changes to a callback
     *
     * Invoking the factory is done like so:
     * <code>
     *    function(listDiff) {
     *       // watch an object
     *       var watcher = listDiff();
     *
     *       // a function that creates a unique hash from each object (e.g. it's key or id)
     *       function hashFn(obj) { return obj.id; }
     *
     *       // a function to read the changeList when a change occurs
     *       function processChanges(changeList) { console.log('changes detected', changeList); }
     *
     *       // attach a listener to the watcher
     *       listDiff.watch($scope, 'variableName', processChanges, hashFn);
     *
     *       // directly process two arrays
     *       var changeList = watcher.diff( oldArray, newArray, hashFn );
     *    }
     * </code>
     */
    module.factory('listDiff', [
        function() {
            function diff(old, curr, hashFn) {
                var out = {
                    count: 0,
                    added: [],
                    removed: []
                };

                if (!old && curr) {
                    out.added = curr.slice(0);
                } else if (!curr && old) {
                    out.removed = old.slice(0);
                } else if (hashFn) {
                    //todo this could be more efficient (it's possibly worse than o(n) right now)
                    var oldMap = old.map(hashFn),
                        newMap = curr.map(hashFn);
                    out.removed = oldMap.filter(function(x, k) {
                        return !newMap.hasOwnProperty(k);
                    });
                    out.added = newMap.filter(function(x, k) {
                        return !oldMap.hasOwnProperty(k);
                    });
                } else {
                    // these don't work for angularFire because it returns 
                    // different objects in each set and === is used to compare
                    out.removed = old.diff(curr);
                    out.added = curr.diff(old);
                }
                out.count = out.removed.length + out.added.length;
                return out;
            }

            return {
                diff: diff,
                watch: function($scope, varName, callback, hashFn) {
                    //todo add a dispose method
                    return $scope.$watch(varName, function(newVal, oldVal) {
                        var out = diff(oldVal, newVal, hashFn);
                        if (out.count) {
                            callback(out);
                        }
                    }, true);
                }
            };
        }
    ]);

    /**
     * A diff utility that watches a variable in scope, which is assumed to be an object.
     * Any time it changes, the objects are compared (only one level deep) and a list
     * of added, removed, and updated elements is returned to anybody listening on watch().
     *
     * Invoking the factory is done like so:
     * <code>
     *    function(treeDiff) {
     *       // watch an object
     *       var watcher = treeDiff($scope, 'variableName');
     *
     *       // attach a listener to the watcher
     *       watcher.watch(function(changeList) {
     *           console.log('changes detected', changeList);
     *       });
     *
     *       // manually process an object
     *       var changeList = watcher.diff( oldObject, newObject );
     *    }
     * </code>
     *
     * The return value of that call contains an object with three methods:
     *    diff:  do a one-time diff of two arrays
     *    watch: add an observer to be notified of any changes
     *    orig:  when using watch() this method returns the old object before it changed
     */
    module.factory('treeDiff', function() {
        return function($scope, variableName) {
            var orig = angular.copy($scope[variableName]);
            var listeners = [];

            function update(newVal) {
                newVal || (newVal = {});
                var changes = diff(orig, newVal);
                if (changes.count) {
                    notify(changes, newVal, orig);
                    orig = angular.copy(newVal);
                }
            }

            function diff(orig, updated) {
                var newKeys = Object.keys(updated),
                    oldKeys = Object.keys(orig);
                var removed = oldKeys.diff(newKeys);
                var added = newKeys.diff(oldKeys);
                var union = newKeys.union(oldKeys);

                var changes = {
                    count: removed.length + added.length,
                    added: added,
                    removed: removed,
                    updated: []
                };

                union.forEach(function(k) {
                    if (!angular.equals(orig[k], updated[k])) {
                        changes.updated.push(k);
                        changes.count++;
                    }
                });

                return changes;
            }

            function notify(changes, newVal, orig) {
                listeners.each(function(fn) {
                    fn(changes, newVal, orig);
                });
            }

            $scope.$watch(variableName, update, true);

            return {
                orig: function() {
                    return orig;
                },
                diff: diff,
                watch: function(callback) {
                    listeners.push(callback);
                }
            }
        }
    });

    return module;

});

in line 157, please replace "listeners.each" with "listeners.forEach"