//     Backbone.js 1.1.0

//     (c) 2010-2011 Jeremy Ashkenas, DocumentCloud Inc.
//     (c) 2011-2013 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
//     Backbone may be freely distributed under the MIT license.
//     For all details and documentation:
//     http://backbonejs.org

(function () {
  // Initial Setup
  // -------------

  // Save a reference to the global object (`window` in the browser, `exports`
  // on the server).
  var root = this;

  // Save the previous value of the `Backbone` variable, so that it can be
  // restored later on, if `noConflict` is used.
  var previousBackbone = root.Backbone;

  // Create local references to array methods we'll want to use later.
  var array = [];
  var push = array.push;
  var slice = array.slice;
  var splice = array.splice;

  // The top-level namespace. All public Backbone classes and modules will
  // be attached to this. Exported for both the browser and the server.
  var Backbone;
  if (typeof exports !== "undefined") {
    Backbone = exports;
  } else {
    Backbone = root.Backbone = {};
  }

  // Current version of the library. Keep in sync with `package.json`.
  Backbone.VERSION = "1.1.0";

  // Require Underscore, if we're on the server, and it's not already present.
  var _ = root._;
  if (!_ && typeof require !== "undefined") _ = require("underscore");

  // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
  // the `$` variable.
  Backbone.$ = root.jQuery || root.Zepto || root.ender || root.$;

  // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
  // to its previous owner. Returns a reference to this Backbone object.
  Backbone.noConflict = function () {
    root.Backbone = previousBackbone;
    return this;
  };

  // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option
  // will fake `"PATCH"`, `"PUT"` and `"DELETE"` requests via the `_method` parameter and
  // set a `X-Http-Method-Override` header.
  Backbone.emulateHTTP = false;

  // Turn on `emulateJSON` to support legacy servers that can't deal with direct
  // `application/json` requests ... will encode the body as
  // `application/x-www-form-urlencoded` instead and will send the model in a
  // form param named `model`.
  Backbone.emulateJSON = false;

  // Backbone.Events
  // ---------------

  // A module that can be mixed in to *any object* in order to provide it with
  // custom events. You may bind with `on` or remove with `off` callback
  // functions to an event; `trigger`-ing an event fires all callbacks in
  // succession.
  //
  //     var object = {};
  //     _.extend(object, Backbone.Events);
  //     object.on('expand', function(){ alert('expanded'); });
  //     object.trigger('expand');
  //
  var Events = (Backbone.Events = {
    // Bind an event to a `callback` function. Passing `"all"` will bind
    // the callback to all events fired.
    on: function (name, callback, context) {
      if (!eventsApi(this, "on", name, [callback, context]) || !callback)
        return this;
      this._events || (this._events = {});
      var events = this._events[name] || (this._events[name] = []);
      events.push({
        callback: callback,
        context: context,
        ctx: context || this,
      });
      return this;
    },

    // Bind an event to only be triggered a single time. After the first time
    // the callback is invoked, it will be removed.
    once: function (name, callback, context) {
      if (!eventsApi(this, "once", name, [callback, context]) || !callback)
        return this;
      var self = this;
      var once = _.once(function () {
        self.off(name, once);
        callback.apply(this, arguments);
      });
      once._callback = callback;
      return this.on(name, once, context);
    },

    // Remove one or many callbacks. If `context` is null, removes all
    // callbacks with that function. If `callback` is null, removes all
    // callbacks for the event. If `name` is null, removes all bound
    // callbacks for all events.
    off: function (name, callback, context) {
      var retain, ev, events, names, i, l, j, k;
      if (!this._events || !eventsApi(this, "off", name, [callback, context]))
        return this;
      if (!name && !callback && !context) {
        this._events = {};
        return this;
      }
      names = name ? [name] : _.keys(this._events);
      for (i = 0, l = names.length; i < l; i++) {
        name = names[i];
        if ((events = this._events[name])) {
          this._events[name] = retain = [];
          if (callback || context) {
            for (j = 0, k = events.length; j < k; j++) {
              ev = events[j];
              if (
                (callback &&
                  callback !== ev.callback &&
                  callback !== ev.callback._callback) ||
                (context && context !== ev.context)
              ) {
                retain.push(ev);
              }
            }
          }
          if (!retain.length) delete this._events[name];
        }
      }

      return this;
    },

    // Trigger one or many events, firing all bound callbacks. Callbacks are
    // passed the same arguments as `trigger` is, apart from the event name
    // (unless you're listening on `"all"`, which will cause your callback to
    // receive the true name of the event as the first argument).
    trigger: function (name) {
      if (!this._events) return this;
      var args = slice.call(arguments, 1);
      if (!eventsApi(this, "trigger", name, args)) return this;
      var events = this._events[name];
      var allEvents = this._events.all;
      if (events) triggerEvents(events, args);
      if (allEvents) triggerEvents(allEvents, arguments);
      return this;
    },

    // Tell this object to stop listening to either specific events ... or
    // to every object it's currently listening to.
    stopListening: function (obj, name, callback) {
      var listeningTo = this._listeningTo;
      if (!listeningTo) return this;
      var remove = !name && !callback;
      if (!callback && typeof name === "object") callback = this;
      if (obj) (listeningTo = {})[obj._listenId] = obj;
      for (var id in listeningTo) {
        obj = listeningTo[id];
        obj.off(name, callback, this);
        if (remove || _.isEmpty(obj._events)) delete this._listeningTo[id];
      }
      return this;
    },
  });

  // Regular expression used to split event strings.
  var eventSplitter = /\s+/;

  // Implement fancy features of the Events API such as multiple event
  // names `"change blur"` and jQuery-style event maps `{change: action}`
  // in terms of the existing API.
  var eventsApi = function (obj, action, name, rest) {
    if (!name) return true;

    // Handle event maps.
    if (typeof name === "object") {
      for (var key in name) {
        obj[action].apply(obj, [key, name[key]].concat(rest));
      }
      return false;
    }

    // Handle space separated event names.
    if (eventSplitter.test(name)) {
      var names = name.split(eventSplitter);
      for (var i = 0, l = names.length; i < l; i++) {
        obj[action].apply(obj, [names[i]].concat(rest));
      }
      return false;
    }

    return true;
  };

  // A difficult-to-believe, but optimized internal dispatch function for
  // triggering events. Tries to keep the usual cases speedy (most internal
  // Backbone events have 3 arguments).
  var triggerEvents = function (events, args) {
    var ev,
      i = -1,
      l = events.length,
      a1 = args[0],
      a2 = args[1],
      a3 = args[2];
    switch (args.length) {
      case 0:
        while (++i < l) (ev = events[i]).callback.call(ev.ctx);
        return;
      case 1:
        while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1);
        return;
      case 2:
        while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2);
        return;
      case 3:
        while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3);
        return;
      default:
        while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args);
    }
  };

  var listenMethods = { listenTo: "on", listenToOnce: "once" };

  // Inversion-of-control versions of `on` and `once`. Tell *this* object to
  // listen to an event in another object ... keeping track of what it's
  // listening to.
  _.each(listenMethods, function (implementation, method) {
    Events[method] = function (obj, name, callback) {
      var listeningTo = this._listeningTo || (this._listeningTo = {});
      var id = obj._listenId || (obj._listenId = _.uniqueId("l"));
      listeningTo[id] = obj;
      if (!callback && typeof name === "object") callback = this;
      obj[implementation](name, callback, this);
      return this;
    };
  });

  // Aliases for backwards compatibility.
  Events.bind = Events.on;
  Events.unbind = Events.off;

  // Allow the `Backbone` object to serve as a global event bus, for folks who
  // want global "pubsub" in a convenient place.
  _.extend(Backbone, Events);

  // Backbone.Model
  // --------------

  // Backbone **Models** are the basic data object in the framework --
  // frequently representing a row in a table in a database on your server.
  // A discrete chunk of data and a bunch of useful, related methods for
  // performing computations and transformations on that data.

  // Create a new model with the specified attributes. A client id (`cid`)
  // is automatically generated and assigned for you.
  var Model = (Backbone.Model = function (attributes, options) {
    var attrs = attributes || {};
    options || (options = {});
    this.cid = _.uniqueId("c");
    this.attributes = {};
    if (options.collection) this.collection = options.collection;
    if (options.parse) attrs = this.parse(attrs, options) || {};
    attrs = _.defaults({}, attrs, _.result(this, "defaults"));
    this.set(attrs, options);
    this.changed = {};
    this.initialize.apply(this, arguments);
  });

  // Attach all inheritable methods to the Model prototype.
  _.extend(Model.prototype, Events, {
    // A hash of attributes whose current and previous value differ.
    changed: null,

    // The value returned during the last failed validation.
    validationError: null,

    // The default name for the JSON `id` attribute is `"id"`. MongoDB and
    // CouchDB users may want to set this to `"_id"`.
    idAttribute: "id",

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize: function () {},

    // Return a copy of the model's `attributes` object.
    toJSON: function (options) {
      return _.clone(this.attributes);
    },

    // Proxy `Backbone.sync` by default -- but override this if you need
    // custom syncing semantics for *this* particular model.
    sync: function () {
      return Backbone.sync.apply(this, arguments);
    },

    // Get the value of an attribute.
    get: function (attr) {
      return this.attributes[attr];
    },

    // Get the HTML-escaped value of an attribute.
    escape: function (attr) {
      return _.escape(this.get(attr));
    },

    // Returns `true` if the attribute contains a value that is not null
    // or undefined.
    has: function (attr) {
      return this.get(attr) != null;
    },

    // Set a hash of model attributes on the object, firing `"change"`. This is
    // the core primitive operation of a model, updating the data and notifying
    // anyone who needs to know about the change in state. The heart of the beast.
    set: function (key, val, options) {
      var attr, attrs, unset, changes, silent, changing, prev, current;
      if (key == null) return this;

      // Handle both `"key", value` and `{key: value}` -style arguments.
      if (typeof key === "object") {
        attrs = key;
        options = val;
      } else {
        (attrs = {})[key] = val;
      }

      options || (options = {});

      // Run validation.
      if (!this._validate(attrs, options)) return false;

      // Extract attributes and options.
      unset = options.unset;
      silent = options.silent;
      changes = [];
      changing = this._changing;
      this._changing = true;

      if (!changing) {
        this._previousAttributes = _.clone(this.attributes);
        this.changed = {};
      }
      (current = this.attributes), (prev = this._previousAttributes);

      // Check for changes of `id`.
      if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];

      // For each `set` attribute, update or delete the current value.
      for (attr in attrs) {
        val = attrs[attr];
        if (!_.isEqual(current[attr], val)) changes.push(attr);
        if (!_.isEqual(prev[attr], val)) {
          this.changed[attr] = val;
        } else {
          delete this.changed[attr];
        }
        unset ? delete current[attr] : (current[attr] = val);
      }

      // Trigger all relevant attribute changes.
      if (!silent) {
        if (changes.length) this._pending = true;
        for (var i = 0, l = changes.length; i < l; i++) {
          this.trigger(
            "change:" + changes[i],
            this,
            current[changes[i]],
            options,
          );
        }
      }

      // You might be wondering why there's a `while` loop here. Changes can
      // be recursively nested within `"change"` events.
      if (changing) return this;
      if (!silent) {
        while (this._pending) {
          this._pending = false;
          this.trigger("change", this, options);
        }
      }
      this._pending = false;
      this._changing = false;
      return this;
    },

    // Remove an attribute from the model, firing `"change"`. `unset` is a noop
    // if the attribute doesn't exist.
    unset: function (attr, options) {
      return this.set(attr, void 0, _.extend({}, options, { unset: true }));
    },

    // Clear all attributes on the model, firing `"change"`.
    clear: function (options) {
      var attrs = {};
      for (var key in this.attributes) attrs[key] = void 0;
      return this.set(attrs, _.extend({}, options, { unset: true }));
    },

    // Determine if the model has changed since the last `"change"` event.
    // If you specify an attribute name, determine if that attribute has changed.
    hasChanged: function (attr) {
      if (attr == null) return !_.isEmpty(this.changed);
      return _.has(this.changed, attr);
    },

    // Return an object containing all the attributes that have changed, or
    // false if there are no changed attributes. Useful for determining what
    // parts of a view need to be updated and/or what attributes need to be
    // persisted to the server. Unset attributes will be set to undefined.
    // You can also pass an attributes object to diff against the model,
    // determining if there *would be* a change.
    changedAttributes: function (diff) {
      if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
      var val,
        changed = false;
      var old = this._changing ? this._previousAttributes : this.attributes;
      for (var attr in diff) {
        if (_.isEqual(old[attr], (val = diff[attr]))) continue;
        (changed || (changed = {}))[attr] = val;
      }
      return changed;
    },

    // Get the previous value of an attribute, recorded at the time the last
    // `"change"` event was fired.
    previous: function (attr) {
      if (attr == null || !this._previousAttributes) return null;
      return this._previousAttributes[attr];
    },

    // Get all of the attributes of the model at the time of the previous
    // `"change"` event.
    previousAttributes: function () {
      return _.clone(this._previousAttributes);
    },

    // Fetch the model from the server. If the server's representation of the
    // model differs from its current attributes, they will be overridden,
    // triggering a `"change"` event.
    fetch: function (options) {
      options = options ? _.clone(options) : {};
      if (options.parse === void 0) options.parse = true;
      var model = this;
      var success = options.success;
      options.success = function (resp) {
        if (!model.set(model.parse(resp, options), options)) return false;
        if (success) success(model, resp, options);
        model.trigger("sync", model, resp, options);
      };
      wrapError(this, options);
      return this.sync("read", this, options);
    },

    // Set a hash of model attributes, and sync the model to the server.
    // If the server returns an attributes hash that differs, the model's
    // state will be `set` again.
    save: function (key, val, options) {
      var attrs,
        method,
        xhr,
        attributes = this.attributes;

      // Handle both `"key", value` and `{key: value}` -style arguments.
      if (key == null || typeof key === "object") {
        attrs = key;
        options = val;
      } else {
        (attrs = {})[key] = val;
      }

      options = _.extend({ validate: true }, options);

      // If we're not waiting and attributes exist, save acts as
      // `set(attr).save(null, opts)` with validation. Otherwise, check if
      // the model will be valid when the attributes, if any, are set.
      if (attrs && !options.wait) {
        if (!this.set(attrs, options)) return false;
      } else {
        if (!this._validate(attrs, options)) return false;
      }

      // Set temporary attributes if `{wait: true}`.
      if (attrs && options.wait) {
        this.attributes = _.extend({}, attributes, attrs);
      }

      // After a successful server-side save, the client is (optionally)
      // updated with the server-side state.
      if (options.parse === void 0) options.parse = true;
      var model = this;
      var success = options.success;
      options.success = function (resp) {
        // Ensure attributes are restored during synchronous saves.
        model.attributes = attributes;
        var serverAttrs = model.parse(resp, options);
        if (options.wait) serverAttrs = _.extend(attrs || {}, serverAttrs);
        if (_.isObject(serverAttrs) && !model.set(serverAttrs, options)) {
          return false;
        }
        if (success) success(model, resp, options);
        model.trigger("sync", model, resp, options);
      };
      wrapError(this, options);

      method = this.isNew() ? "create" : options.patch ? "patch" : "update";
      if (method === "patch") options.attrs = attrs;
      xhr = this.sync(method, this, options);

      // Restore attributes.
      if (attrs && options.wait) this.attributes = attributes;

      return xhr;
    },

    // Destroy this model on the server if it was already persisted.
    // Optimistically removes the model from its collection, if it has one.
    // If `wait: true` is passed, waits for the server to respond before removal.
    destroy: function (options) {
      options = options ? _.clone(options) : {};
      var model = this;
      var success = options.success;

      var destroy = function () {
        model.trigger("destroy", model, model.collection, options);
      };

      options.success = function (resp) {
        if (options.wait || model.isNew()) destroy();
        if (success) success(model, resp, options);
        if (!model.isNew()) model.trigger("sync", model, resp, options);
      };

      if (this.isNew()) {
        options.success();
        return false;
      }
      wrapError(this, options);

      var xhr = this.sync("delete", this, options);
      if (!options.wait) destroy();
      return xhr;
    },

    // Default URL for the model's representation on the server -- if you're
    // using Backbone's restful methods, override this to change the endpoint
    // that will be called.
    url: function () {
      var base =
        _.result(this, "urlRoot") ||
        _.result(this.collection, "url") ||
        urlError();
      if (this.isNew()) return base;
      return (
        base +
        (base.charAt(base.length - 1) === "/" ? "" : "/") +
        encodeURIComponent(this.id)
      );
    },

    // **parse** converts a response into the hash of attributes to be `set` on
    // the model. The default implementation is just to pass the response along.
    parse: function (resp, options) {
      return resp;
    },

    // Create a new model with identical attributes to this one.
    clone: function () {
      return new this.constructor(this.attributes);
    },

    // A model is new if it has never been saved to the server, and lacks an id.
    isNew: function () {
      return this.id == null;
    },

    // Check if the model is currently in a valid state.
    isValid: function (options) {
      return this._validate({}, _.extend(options || {}, { validate: true }));
    },

    // Run validation against the next complete set of model attributes,
    // returning `true` if all is well. Otherwise, fire an `"invalid"` event.
    _validate: function (attrs, options) {
      if (!options.validate || !this.validate) return true;
      attrs = _.extend({}, this.attributes, attrs);
      var error = (this.validationError =
        this.validate(attrs, options) || null);
      if (!error) return true;
      this.trigger(
        "invalid",
        this,
        error,
        _.extend(options, { validationError: error }),
      );
      return false;
    },
  });

  // Underscore methods that we want to implement on the Model.
  var modelMethods = ["keys", "values", "pairs", "invert", "pick", "omit"];

  // Mix in each Underscore method as a proxy to `Model#attributes`.
  _.each(modelMethods, function (method) {
    Model.prototype[method] = function () {
      var args = slice.call(arguments);
      args.unshift(this.attributes);
      return _[method].apply(_, args);
    };
  });

  // Backbone.Collection
  // -------------------

  // If models tend to represent a single row of data, a Backbone Collection is
  // more analagous to a table full of data ... or a small slice or page of that
  // table, or a collection of rows that belong together for a particular reason
  // -- all of the messages in this particular folder, all of the documents
  // belonging to this particular author, and so on. Collections maintain
  // indexes of their models, both in order, and for lookup by `id`.

  // Create a new **Collection**, perhaps to contain a specific type of `model`.
  // If a `comparator` is specified, the Collection will maintain
  // its models in sort order, as they're added and removed.
  var Collection = (Backbone.Collection = function (models, options) {
    options || (options = {});
    if (options.model) this.model = options.model;
    if (options.comparator !== void 0) this.comparator = options.comparator;
    this._reset();
    this.initialize.apply(this, arguments);
    if (models) this.reset(models, _.extend({ silent: true }, options));
  });

  // Default options for `Collection#set`.
  var setOptions = { add: true, remove: true, merge: true };
  var addOptions = { add: true, remove: false };

  // Define the Collection's inheritable methods.
  _.extend(Collection.prototype, Events, {
    // The default model for a collection is just a **Backbone.Model**.
    // This should be overridden in most cases.
    model: Model,

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize: function () {},

    // The JSON representation of a Collection is an array of the
    // models' attributes.
    toJSON: function (options) {
      return this.map(function (model) {
        return model.toJSON(options);
      });
    },

    // Proxy `Backbone.sync` by default.
    sync: function () {
      return Backbone.sync.apply(this, arguments);
    },

    // Add a model, or list of models to the set.
    add: function (models, options) {
      return this.set(models, _.extend({ merge: false }, options, addOptions));
    },

    // Remove a model, or a list of models from the set.
    remove: function (models, options) {
      var singular = !_.isArray(models);
      models = singular ? [models] : _.clone(models);
      options || (options = {});
      var i, l, index, model;
      for (i = 0, l = models.length; i < l; i++) {
        model = models[i] = this.get(models[i]);
        if (!model) continue;
        delete this._byId[model.id];
        delete this._byId[model.cid];
        index = this.indexOf(model);
        this.models.splice(index, 1);
        this.length--;
        if (!options.silent) {
          options.index = index;
          model.trigger("remove", model, this, options);
        }
        this._removeReference(model);
      }
      return singular ? models[0] : models;
    },

    // Update a collection by `set`-ing a new list of models, adding new ones,
    // removing models that are no longer present, and merging models that
    // already exist in the collection, as necessary. Similar to **Model#set**,
    // the core operation for updating the data contained by the collection.
    set: function (models, options) {
      options = _.defaults({}, options, setOptions);
      if (options.parse) models = this.parse(models, options);
      var singular = !_.isArray(models);
      models = singular ? (models ? [models] : []) : _.clone(models);
      var i, l, id, model, attrs, existing, sort;
      var at = options.at;
      var targetModel = this.model;
      var sortable = this.comparator && at == null && options.sort !== false;
      var sortAttr = _.isString(this.comparator) ? this.comparator : null;
      var toAdd = [],
        toRemove = [],
        modelMap = {};
      var add = options.add,
        merge = options.merge,
        remove = options.remove;
      var order = !sortable && add && remove ? [] : false;

      // Turn bare objects into model references, and prevent invalid models
      // from being added.
      for (i = 0, l = models.length; i < l; i++) {
        attrs = models[i];
        if (attrs instanceof Model) {
          id = model = attrs;
        } else {
          id = attrs[targetModel.prototype.idAttribute];
        }

        // If a duplicate is found, prevent it from being added and
        // optionally merge it into the existing model.
        if ((existing = this.get(id))) {
          if (remove) modelMap[existing.cid] = true;
          if (merge) {
            attrs = attrs === model ? model.attributes : attrs;
            if (options.parse) attrs = existing.parse(attrs, options);
            existing.set(attrs, options);
            if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;
          }
          models[i] = existing;

          // If this is a new, valid model, push it to the `toAdd` list.
        } else if (add) {
          model = models[i] = this._prepareModel(attrs, options);
          if (!model) continue;
          toAdd.push(model);

          // Listen to added models' events, and index models for lookup by
          // `id` and by `cid`.
          model.on("all", this._onModelEvent, this);
          this._byId[model.cid] = model;
          if (model.id != null) this._byId[model.id] = model;
        }
        if (order) order.push(existing || model);
      }

      // Remove nonexistent models if appropriate.
      if (remove) {
        for (i = 0, l = this.length; i < l; ++i) {
          if (!modelMap[(model = this.models[i]).cid]) toRemove.push(model);
        }
        if (toRemove.length) this.remove(toRemove, options);
      }

      // See if sorting is needed, update `length` and splice in new models.
      if (toAdd.length || (order && order.length)) {
        if (sortable) sort = true;
        this.length += toAdd.length;
        if (at != null) {
          for (i = 0, l = toAdd.length; i < l; i++) {
            this.models.splice(at + i, 0, toAdd[i]);
          }
        } else {
          if (order) this.models.length = 0;
          var orderedModels = order || toAdd;
          for (i = 0, l = orderedModels.length; i < l; i++) {
            this.models.push(orderedModels[i]);
          }
        }
      }

      // Silently sort the collection if appropriate.
      if (sort) this.sort({ silent: true });

      // Unless silenced, it's time to fire all appropriate add/sort events.
      if (!options.silent) {
        for (i = 0, l = toAdd.length; i < l; i++) {
          (model = toAdd[i]).trigger("add", model, this, options);
        }
        if (sort || (order && order.length))
          this.trigger("sort", this, options);
      }

      // Return the added (or merged) model (or models).
      return singular ? models[0] : models;
    },

    // When you have more items than you want to add or remove individually,
    // you can reset the entire set with a new list of models, without firing
    // any granular `add` or `remove` events. Fires `reset` when finished.
    // Useful for bulk operations and optimizations.
    reset: function (models, options) {
      options || (options = {});
      for (var i = 0, l = this.models.length; i < l; i++) {
        this._removeReference(this.models[i]);
      }
      options.previousModels = this.models;
      this._reset();
      models = this.add(models, _.extend({ silent: true }, options));
      if (!options.silent) this.trigger("reset", this, options);
      return models;
    },

    // Add a model to the end of the collection.
    push: function (model, options) {
      return this.add(model, _.extend({ at: this.length }, options));
    },

    // Remove a model from the end of the collection.
    pop: function (options) {
      var model = this.at(this.length - 1);
      this.remove(model, options);
      return model;
    },

    // Add a model to the beginning of the collection.
    unshift: function (model, options) {
      return this.add(model, _.extend({ at: 0 }, options));
    },

    // Remove a model from the beginning of the collection.
    shift: function (options) {
      var model = this.at(0);
      this.remove(model, options);
      return model;
    },

    // Slice out a sub-array of models from the collection.
    slice: function () {
      return slice.apply(this.models, arguments);
    },

    // Get a model from the set by id.
    get: function (obj) {
      if (obj == null) return void 0;
      return this._byId[obj.id] || this._byId[obj.cid] || this._byId[obj];
    },

    // Get the model at the given index.
    at: function (index) {
      return this.models[index];
    },

    // Return models with matching attributes. Useful for simple cases of
    // `filter`.
    where: function (attrs, first) {
      if (_.isEmpty(attrs)) return first ? void 0 : [];
      return this[first ? "find" : "filter"](function (model) {
        for (var key in attrs) {
          if (attrs[key] !== model.get(key)) return false;
        }
        return true;
      });
    },

    // Return the first model with matching attributes. Useful for simple cases
    // of `find`.
    findWhere: function (attrs) {
      return this.where(attrs, true);
    },

    // Force the collection to re-sort itself. You don't need to call this under
    // normal circumstances, as the set will maintain sort order as each item
    // is added.
    sort: function (options) {
      if (!this.comparator)
        throw new Error("Cannot sort a set without a comparator");
      options || (options = {});

      // Run sort based on type of `comparator`.
      if (_.isString(this.comparator) || this.comparator.length === 1) {
        this.models = this.sortBy(this.comparator, this);
      } else {
        this.models.sort(_.bind(this.comparator, this));
      }

      if (!options.silent) this.trigger("sort", this, options);
      return this;
    },

    // Pluck an attribute from each model in the collection.
    pluck: function (attr) {
      return _.invoke(this.models, "get", attr);
    },

    // Fetch the default set of models for this collection, resetting the
    // collection when they arrive. If `reset: true` is passed, the response
    // data will be passed through the `reset` method instead of `set`.
    fetch: function (options) {
      options = options ? _.clone(options) : {};
      if (options.parse === void 0) options.parse = true;
      var success = options.success;
      var collection = this;
      options.success = function (resp) {
        var method = options.reset ? "reset" : "set";
        collection[method](resp, options);
        if (success) success(collection, resp, options);
        collection.trigger("sync", collection, resp, options);
      };
      wrapError(this, options);
      return this.sync("read", this, options);
    },

    // Create a new instance of a model in this collection. Add the model to the
    // collection immediately, unless `wait: true` is passed, in which case we
    // wait for the server to agree.
    create: function (model, options) {
      options = options ? _.clone(options) : {};
      if (!(model = this._prepareModel(model, options))) return false;
      if (!options.wait) this.add(model, options);
      var collection = this;
      var success = options.success;
      options.success = function (model, resp, options) {
        if (options.wait) collection.add(model, options);
        if (success) success(model, resp, options);
      };
      model.save(null, options);
      return model;
    },

    // **parse** converts a response into a list of models to be added to the
    // collection. The default implementation is just to pass it through.
    parse: function (resp, options) {
      return resp;
    },

    // Create a new collection with an identical list of models as this one.
    clone: function () {
      return new this.constructor(this.models);
    },

    // Private method to reset all internal state. Called when the collection
    // is first initialized or reset.
    _reset: function () {
      this.length = 0;
      this.models = [];
      this._byId = {};
    },

    // Prepare a hash of attributes (or other model) to be added to this
    // collection.
    _prepareModel: function (attrs, options) {
      if (attrs instanceof Model) {
        if (!attrs.collection) attrs.collection = this;
        return attrs;
      }
      options = options ? _.clone(options) : {};
      options.collection = this;
      var model = new this.model(attrs, options);
      if (!model.validationError) return model;
      this.trigger("invalid", this, model.validationError, options);
      return false;
    },

    // Internal method to sever a model's ties to a collection.
    _removeReference: function (model) {
      if (this === model.collection) delete model.collection;
      model.off("all", this._onModelEvent, this);
    },

    // Internal method called every time a model in the set fires an event.
    // Sets need to update their indexes when models change ids. All other
    // events simply proxy through. "add" and "remove" events that originate
    // in other collections are ignored.
    _onModelEvent: function (event, model, collection, options) {
      if ((event === "add" || event === "remove") && collection !== this)
        return;
      if (event === "destroy") this.remove(model, options);
      if (model && event === "change:" + model.idAttribute) {
        delete this._byId[model.previous(model.idAttribute)];
        if (model.id != null) this._byId[model.id] = model;
      }
      this.trigger.apply(this, arguments);
    },
  });

  // Underscore methods that we want to implement on the Collection.
  // 90% of the core usefulness of Backbone Collections is actually implemented
  // right here:
  var methods = [
    "forEach",
    "each",
    "map",
    "collect",
    "reduce",
    "foldl",
    "inject",
    "reduceRight",
    "foldr",
    "find",
    "detect",
    "filter",
    "select",
    "reject",
    "every",
    "all",
    "some",
    "any",
    "include",
    "contains",
    "invoke",
    "max",
    "min",
    "toArray",
    "size",
    "first",
    "head",
    "take",
    "initial",
    "rest",
    "tail",
    "drop",
    "last",
    "without",
    "difference",
    "indexOf",
    "shuffle",
    "lastIndexOf",
    "isEmpty",
    "chain",
  ];

  // Mix in each Underscore method as a proxy to `Collection#models`.
  _.each(methods, function (method) {
    Collection.prototype[method] = function () {
      var args = slice.call(arguments);
      args.unshift(this.models);
      return _[method].apply(_, args);
    };
  });

  // Underscore methods that take a property name as an argument.
  var attributeMethods = ["groupBy", "countBy", "sortBy"];

  // Use attributes instead of properties.
  _.each(attributeMethods, function (method) {
    Collection.prototype[method] = function (value, context) {
      var iterator = _.isFunction(value)
        ? value
        : function (model) {
            return model.get(value);
          };
      return _[method](this.models, iterator, context);
    };
  });

  // Backbone.View
  // -------------

  // Backbone Views are almost more convention than they are actual code. A View
  // is simply a JavaScript object that represents a logical chunk of UI in the
  // DOM. This might be a single item, an entire list, a sidebar or panel, or
  // even the surrounding frame which wraps your whole app. Defining a chunk of
  // UI as a **View** allows you to define your DOM events declaratively, without
  // having to worry about render order ... and makes it easy for the view to
  // react to specific changes in the state of your models.

  // Creating a Backbone.View creates its initial element outside of the DOM,
  // if an existing element is not provided...
  var View = (Backbone.View = function (options) {
    this.cid = _.uniqueId("view");
    options || (options = {});
    _.extend(this, _.pick(options, viewOptions));
    this._ensureElement();
    this.initialize.apply(this, arguments);
    this.delegateEvents();
  });

  // Cached regex to split keys for `delegate`.
  var delegateEventSplitter = /^(\S+)\s*(.*)$/;

  // List of view options to be merged as properties.
  var viewOptions = [
    "model",
    "collection",
    "el",
    "id",
    "attributes",
    "className",
    "tagName",
    "events",
  ];

  // Set up all inheritable **Backbone.View** properties and methods.
  _.extend(View.prototype, Events, {
    // The default `tagName` of a View's element is `"div"`.
    tagName: "div",

    // jQuery delegate for element lookup, scoped to DOM elements within the
    // current view. This should be preferred to global lookups where possible.
    $: function (selector) {
      return this.$el.find(selector);
    },

    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize: function () {},

    // **render** is the core function that your view should override, in order
    // to populate its element (`this.el`), with the appropriate HTML. The
    // convention is for **render** to always return `this`.
    render: function () {
      return this;
    },

    // Remove this view by taking the element out of the DOM, and removing any
    // applicable Backbone.Events listeners.
    remove: function () {
      this.$el.remove();
      this.stopListening();
      return this;
    },

    // Change the view's element (`this.el` property), including event
    // re-delegation.
    setElement: function (element, delegate) {
      if (this.$el) this.undelegateEvents();
      this.$el = element instanceof Backbone.$ ? element : Backbone.$(element);
      this.el = this.$el[0];
      if (delegate !== false) this.delegateEvents();
      return this;
    },

    // Set callbacks, where `this.events` is a hash of
    //
    // *{"event selector": "callback"}*
    //
    //     {
    //       'mousedown .title':  'edit',
    //       'click .button':     'save',
    //       'click .open':       function(e) { ... }
    //     }
    //
    // pairs. Callbacks will be bound to the view, with `this` set properly.
    // Uses event delegation for efficiency.
    // Omitting the selector binds the event to `this.el`.
    // This only works for delegate-able events: not `focus`, `blur`, and
    // not `change`, `submit`, and `reset` in Internet Explorer.
    delegateEvents: function (events) {
      if (!(events || (events = _.result(this, "events")))) return this;
      this.undelegateEvents();
      for (var key in events) {
        var method = events[key];
        if (!_.isFunction(method)) method = this[events[key]];
        if (!method) continue;

        var match = key.match(delegateEventSplitter);
        var eventName = match[1],
          selector = match[2];
        method = _.bind(method, this);
        eventName += ".delegateEvents" + this.cid;
        if (selector === "") {
          this.$el.on(eventName, method);
        } else {
          this.$el.on(eventName, selector, method);
        }
      }
      return this;
    },

    // Clears all callbacks previously bound to the view with `delegateEvents`.
    // You usually don't need to use this, but may wish to if you have multiple
    // Backbone views attached to the same DOM element.
    undelegateEvents: function () {
      this.$el.off(".delegateEvents" + this.cid);
      return this;
    },

    // Ensure that the View has a DOM element to render into.
    // If `this.el` is a string, pass it through `$()`, take the first
    // matching element, and re-assign it to `el`. Otherwise, create
    // an element from the `id`, `className` and `tagName` properties.
    _ensureElement: function () {
      if (!this.el) {
        var attrs = _.extend({}, _.result(this, "attributes"));
        if (this.id) attrs.id = _.result(this, "id");
        if (this.className) attrs["class"] = _.result(this, "className");
        var $el = Backbone.$("<" + _.result(this, "tagName") + ">").attr(attrs);
        this.setElement($el, false);
      } else {
        this.setElement(_.result(this, "el"), false);
      }
    },
  });

  // Backbone.sync
  // -------------

  // Override this function to change the manner in which Backbone persists
  // models to the server. You will be passed the type of request, and the
  // model in question. By default, makes a RESTful Ajax request
  // to the model's `url()`. Some possible customizations could be:
  //
  // * Use `setTimeout` to batch rapid-fire updates into a single request.
  // * Send up the models as XML instead of JSON.
  // * Persist models via WebSockets instead of Ajax.
  //
  // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
  // as `POST`, with a `_method` parameter containing the true HTTP method,
  // as well as all requests with the body as `application/x-www-form-urlencoded`
  // instead of `application/json` with the model in a param named `model`.
  // Useful when interfacing with server-side languages like **PHP** that make
  // it difficult to read the body of `PUT` requests.
  Backbone.sync = function (method, model, options) {
    var type = methodMap[method];

    // Default options, unless specified.
    _.defaults(options || (options = {}), {
      emulateHTTP: Backbone.emulateHTTP,
      emulateJSON: Backbone.emulateJSON,
    });

    // Default JSON-request options.
    var params = { type: type, dataType: "json" };

    // Ensure that we have a URL.
    if (!options.url) {
      params.url = _.result(model, "url") || urlError();
    }

    // Ensure that we have the appropriate request data.
    if (
      options.data == null &&
      model &&
      (method === "create" || method === "update" || method === "patch")
    ) {
      params.contentType = "application/json";
      params.data = JSON.stringify(options.attrs || model.toJSON(options));
    }

    // For older servers, emulate JSON by encoding the request into an HTML-form.
    if (options.emulateJSON) {
      params.contentType = "application/x-www-form-urlencoded";
      params.data = params.data ? { model: params.data } : {};
    }

    // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
    // And an `X-HTTP-Method-Override` header.
    if (
      options.emulateHTTP &&
      (type === "PUT" || type === "DELETE" || type === "PATCH")
    ) {
      params.type = "POST";
      if (options.emulateJSON) params.data._method = type;
      var beforeSend = options.beforeSend;
      options.beforeSend = function (xhr) {
        xhr.setRequestHeader("X-HTTP-Method-Override", type);
        if (beforeSend) return beforeSend.apply(this, arguments);
      };
    }

    // Don't process data on a non-GET request.
    if (params.type !== "GET" && !options.emulateJSON) {
      params.processData = false;
    }

    // If we're sending a `PATCH` request, and we're in an old Internet Explorer
    // that still has ActiveX enabled by default, override jQuery to use that
    // for XHR instead. Remove this line when jQuery supports `PATCH` on IE8.
    if (params.type === "PATCH" && noXhrPatch) {
      params.xhr = function () {
        return new ActiveXObject("Microsoft.XMLHTTP");
      };
    }

    // Make the request, allowing the user to override any Ajax options.
    var xhr = (options.xhr = Backbone.ajax(_.extend(params, options)));
    model.trigger("request", model, xhr, options);
    return xhr;
  };

  var noXhrPatch =
    typeof window !== "undefined" &&
    !!window.ActiveXObject &&
    !(window.XMLHttpRequest && new XMLHttpRequest().dispatchEvent);

  // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
  var methodMap = {
    create: "POST",
    update: "PUT",
    patch: "PATCH",
    delete: "DELETE",
    read: "GET",
  };

  // Set the default implementation of `Backbone.ajax` to proxy through to `$`.
  // Override this if you'd like to use a different library.
  Backbone.ajax = function () {
    return Backbone.$.ajax.apply(Backbone.$, arguments);
  };

  // Backbone.Router
  // ---------------

  // Routers map faux-URLs to actions, and fire events when routes are
  // matched. Creating a new one sets its `routes` hash, if not set statically.
  var Router = (Backbone.Router = function (options) {
    options || (options = {});
    if (options.routes) this.routes = options.routes;
    this._bindRoutes();
    this.initialize.apply(this, arguments);
  });

  // Cached regular expressions for matching named param parts and splatted
  // parts of route strings.
  var optionalParam = /\((.*?)\)/g;
  var namedParam = /(\(\?)?:\w+/g;
  var splatParam = /\*\w+/g;
  var escapeRegExp = /[\-{}\[\]+?.,\\\^$|#\s]/g;

  // Set up all inheritable **Backbone.Router** properties and methods.
  _.extend(Router.prototype, Events, {
    // Initialize is an empty function by default. Override it with your own
    // initialization logic.
    initialize: function () {},

    // Manually bind a single named route to a callback. For example:
    //
    //     this.route('search/:query/p:num', 'search', function(query, num) {
    //       ...
    //     });
    //
    route: function (route, name, callback) {
      if (!_.isRegExp(route)) route = this._routeToRegExp(route);
      if (_.isFunction(name)) {
        callback = name;
        name = "";
      }
      if (!callback) callback = this[name];
      var router = this;
      Backbone.history.route(route, function (fragment) {
        var args = router._extractParameters(route, fragment);
        callback && callback.apply(router, args);
        router.trigger.apply(router, ["route:" + name].concat(args));
        router.trigger("route", name, args);
        Backbone.history.trigger("route", router, name, args);
      });
      return this;
    },

    // Simple proxy to `Backbone.history` to save a fragment into the history.
    navigate: function (fragment, options) {
      Backbone.history.navigate(fragment, options);
      return this;
    },

    // Bind all defined routes to `Backbone.history`. We have to reverse the
    // order of the routes here to support behavior where the most general
    // routes can be defined at the bottom of the route map.
    _bindRoutes: function () {
      if (!this.routes) return;
      this.routes = _.result(this, "routes");
      var route,
        routes = _.keys(this.routes);
      while ((route = routes.pop()) != null) {
        this.route(route, this.routes[route]);
      }
    },

    // Convert a route string into a regular expression, suitable for matching
    // against the current location hash.
    _routeToRegExp: function (route) {
      route = route
        .replace(escapeRegExp, "\\$&")
        .replace(optionalParam, "(?:$1)?")
        .replace(namedParam, function (match, optional) {
          return optional ? match : "([^/]+)";
        })
        .replace(splatParam, "(.*?)");
      return new RegExp("^" + route + "$");
    },

    // Given a route, and a URL fragment that it matches, return the array of
    // extracted decoded parameters. Empty or unmatched parameters will be
    // treated as `null` to normalize cross-browser behavior.
    _extractParameters: function (route, fragment) {
      var params = route.exec(fragment).slice(1);
      return _.map(params, function (param) {
        return param ? decodeURIComponent(param) : null;
      });
    },
  });

  // Backbone.History
  // ----------------

  // Handles cross-browser history management, based on either
  // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
  // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
  // and URL fragments. If the browser supports neither (old IE, natch),
  // falls back to polling.
  var History = (Backbone.History = function () {
    this.handlers = [];
    _.bindAll(this, "checkUrl");

    // Ensure that `History` can be used outside of the browser.
    if (typeof window !== "undefined") {
      this.location = window.location;
      this.history = window.history;
    }
  });

  // Cached regex for stripping a leading hash/slash and trailing space.
  var routeStripper = /^[#\/]|\s+$/g;

  // Cached regex for stripping leading and trailing slashes.
  var rootStripper = /^\/+|\/+$/g;

  // Cached regex for detecting MSIE.
  var isExplorer = /msie [\w.]+/;

  // Cached regex for removing a trailing slash.
  var trailingSlash = /\/$/;

  // Cached regex for stripping urls of hash and query.
  var pathStripper = /[?#].*$/;

  // Has the history handling already been started?
  History.started = false;

  // Set up all inheritable **Backbone.History** properties and methods.
  _.extend(History.prototype, Events, {
    // The default interval to poll for hash changes, if necessary, is
    // twenty times a second.
    interval: 50,

    // Gets the true hash value. Cannot use location.hash directly due to bug
    // in Firefox where location.hash will always be decoded.
    getHash: function (window) {
      var match = (window || this).location.href.match(/#(.*)$/);
      return match ? match[1] : "";
    },

    // Get the cross-browser normalized URL fragment, either from the URL,
    // the hash, or the override.
    getFragment: function (fragment, forcePushState) {
      if (fragment == null) {
        if (this._hasPushState || !this._wantsHashChange || forcePushState) {
          fragment = this.location.pathname;
          var root = this.root.replace(trailingSlash, "");
          if (!fragment.indexOf(root)) fragment = fragment.slice(root.length);
        } else {
          fragment = this.getHash();
        }
      }
      return fragment.replace(routeStripper, "");
    },

    // Start the hash change handling, returning `true` if the current URL matches
    // an existing route, and `false` otherwise.
    start: function (options) {
      if (History.started)
        throw new Error("Backbone.history has already been started");
      History.started = true;

      // Figure out the initial configuration. Do we need an iframe?
      // Is pushState desired ... is it available?
      this.options = _.extend({ root: "/" }, this.options, options);
      this.root = this.options.root;
      this._wantsHashChange = this.options.hashChange !== false;
      this._wantsPushState = !!this.options.pushState;
      this._hasPushState = !!(
        this.options.pushState &&
        this.history &&
        this.history.pushState
      );
      var fragment = this.getFragment();
      var docMode = document.documentMode;
      var oldIE =
        isExplorer.exec(navigator.userAgent.toLowerCase()) &&
        (!docMode || docMode <= 7);

      // Normalize root to always include a leading and trailing slash.
      this.root = ("/" + this.root + "/").replace(rootStripper, "/");

      if (oldIE && this._wantsHashChange) {
        this.iframe = Backbone.$('<iframe src="javascript:0" tabindex="-1" />')
          .hide()
          .appendTo("body")[0].contentWindow;
        this.navigate(fragment);
      }

      // Depending on whether we're using pushState or hashes, and whether
      // 'onhashchange' is supported, determine how we check the URL state.
      if (this._hasPushState) {
        Backbone.$(window).on("popstate", this.checkUrl);
      } else if (this._wantsHashChange && "onhashchange" in window && !oldIE) {
        Backbone.$(window).on("hashchange", this.checkUrl);
      } else if (this._wantsHashChange) {
        this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
      }

      // Determine if we need to change the base url, for a pushState link
      // opened by a non-pushState browser.
      this.fragment = fragment;
      var loc = this.location;
      var atRoot = loc.pathname.replace(/[^\/]$/, "$&/") === this.root;

      // Transition from hashChange to pushState or vice versa if both are
      // requested.
      if (this._wantsHashChange && this._wantsPushState) {
        // If we've started off with a route from a `pushState`-enabled
        // browser, but we're currently in a browser that doesn't support it...
        if (!this._hasPushState && !atRoot) {
          this.fragment = this.getFragment(null, true);
          this.location.replace(
            this.root + this.location.search + "#" + this.fragment,
          );
          // Return immediately as browser will do redirect to new url
          return true;

          // Or if we've started out with a hash-based route, but we're currently
          // in a browser where it could be `pushState`-based instead...
        } else if (this._hasPushState && atRoot && loc.hash) {
          this.fragment = this.getHash().replace(routeStripper, "");
          this.history.replaceState(
            {},
            document.title,
            this.root + this.fragment + loc.search,
          );
        }
      }

      if (!this.options.silent) return this.loadUrl();
    },

    // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
    // but possibly useful for unit testing Routers.
    stop: function () {
      Backbone.$(window)
        .off("popstate", this.checkUrl)
        .off("hashchange", this.checkUrl);
      clearInterval(this._checkUrlInterval);
      History.started = false;
    },

    // Add a route to be tested when the fragment changes. Routes added later
    // may override previous routes.
    route: function (route, callback) {
      this.handlers.unshift({ route: route, callback: callback });
    },

    // Checks the current URL to see if it has changed, and if it has,
    // calls `loadUrl`, normalizing across the hidden iframe.
    checkUrl: function (e) {
      var current = this.getFragment();
      if (current === this.fragment && this.iframe) {
        current = this.getFragment(this.getHash(this.iframe));
      }
      if (current === this.fragment) return false;
      if (this.iframe) this.navigate(current);
      this.loadUrl();
    },

    // Attempt to load the current URL fragment. If a route succeeds with a
    // match, returns `true`. If no defined routes matches the fragment,
    // returns `false`.
    loadUrl: function (fragment) {
      fragment = this.fragment = this.getFragment(fragment);
      return _.any(this.handlers, function (handler) {
        if (handler.route.test(fragment)) {
          handler.callback(fragment);
          return true;
        }
      });
    },

    // Save a fragment into the hash history, or replace the URL state if the
    // 'replace' option is passed. You are responsible for properly URL-encoding
    // the fragment in advance.
    //
    // The options object can contain `trigger: true` if you wish to have the
    // route callback be fired (not usually desirable), or `replace: true`, if
    // you wish to modify the current URL without adding an entry to the history.
    navigate: function (fragment, options) {
      if (!History.started) return false;
      if (!options || options === true) options = { trigger: !!options };

      var url = this.root + (fragment = this.getFragment(fragment || ""));

      // Strip the fragment of the query and hash for matching.
      fragment = fragment.replace(pathStripper, "");

      if (this.fragment === fragment) return;
      this.fragment = fragment;

      // Don't include a trailing slash on the root.
      if (fragment === "" && url !== "/") url = url.slice(0, -1);

      // If pushState is available, we use it to set the fragment as a real URL.
      if (this._hasPushState) {
        this.history[options.replace ? "replaceState" : "pushState"](
          {},
          document.title,
          url,
        );

        // If hash changes haven't been explicitly disabled, update the hash
        // fragment to store history.
      } else if (this._wantsHashChange) {
        this._updateHash(this.location, fragment, options.replace);
        if (
          this.iframe &&
          fragment !== this.getFragment(this.getHash(this.iframe))
        ) {
          // Opening and closing the iframe tricks IE7 and earlier to push a
          // history entry on hash-tag change.  When replace is true, we don't
          // want this.
          if (!options.replace) this.iframe.document.open().close();
          this._updateHash(this.iframe.location, fragment, options.replace);
        }

        // If you've told us that you explicitly don't want fallback hashchange-
        // based history, then `navigate` becomes a page refresh.
      } else {
        return this.location.assign(url);
      }
      if (options.trigger) return this.loadUrl(fragment);
    },

    // Update the hash location, either replacing the current entry, or adding
    // a new one to the browser history.
    _updateHash: function (location, fragment, replace) {
      if (replace) {
        var href = location.href.replace(/(javascript:|#).*$/, "");
        location.replace(href + "#" + fragment);
      } else {
        // Some browsers require that `hash` contains a leading #.
        location.hash = "#" + fragment;
      }
    },
  });

  // Create the default Backbone.history.
  Backbone.history = new History();

  // Helpers
  // -------

  // Helper function to correctly set up the prototype chain, for subclasses.
  // Similar to `goog.inherits`, but uses a hash of prototype properties and
  // class properties to be extended.
  var extend = function (protoProps, staticProps) {
    var parent = this;
    var child;

    // The constructor function for the new subclass is either defined by you
    // (the "constructor" property in your `extend` definition), or defaulted
    // by us to simply call the parent's constructor.
    if (protoProps && _.has(protoProps, "constructor")) {
      child = protoProps.constructor;
    } else {
      child = function () {
        return parent.apply(this, arguments);
      };
    }

    // Add static properties to the constructor function, if supplied.
    _.extend(child, parent, staticProps);

    // Set the prototype chain to inherit from `parent`, without calling
    // `parent`'s constructor function.
    var Surrogate = function () {
      this.constructor = child;
    };
    Surrogate.prototype = parent.prototype;
    child.prototype = new Surrogate();

    // Add prototype properties (instance properties) to the subclass,
    // if supplied.
    if (protoProps) _.extend(child.prototype, protoProps);

    // Set a convenience property in case the parent's prototype is needed
    // later.
    child.__super__ = parent.prototype;

    return child;
  };

  // Set up inheritance for the model, collection, router, view and history.
  Model.extend =
    Collection.extend =
    Router.extend =
    View.extend =
    History.extend =
      extend;

  // Throw an error when a URL is needed, and none is supplied.
  var urlError = function () {
    throw new Error('A "url" property or function must be specified');
  };

  // Wrap an optional error callback with a fallback error event.
  var wrapError = function (model, options) {
    var error = options.error;
    options.error = function (resp) {
      if (error) error(model, resp, options);
      model.trigger("error", model, resp, options);
    };
  };
}.call(this));