Fix serialization of models from js -> kernel

IPython/html/static/widgets/js/types.js

@@ -1,35 +1,37
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define([
     "base/js/utils"
 ], function(utils){
     return {
         models: {
             deserialize: function deserialize_models(value, model) {
                 /**
                  * Replace model ids with models recursively.
                  */
                 var unpacked;
                 if ($.isArray(value)) {
                     unpacked = [];
                     _.each(value, function(sub_value, key) {
                         unpacked.push(deserialize_models(sub_value, model));
                     });
                     return Promise.all(unpacked);
                 } else if (value instanceof Object) {
                     unpacked = {};
                     _.each(value, function(sub_value, key) {
                         unpacked[key] = deserialize_models(sub_value, model);
                     });
                     return utils.resolve_promises_dict(unpacked);
                 } else if (typeof value === 'string' && value.slice(0,10) === "IPY_MODEL_") {
                     // get_model returns a promise already
                     return model.widget_manager.get_model(value.slice(10, value.length));
                 } else {
                     return Promise.resolve(value);
                 }
             },
+            /* We don't need a serializer since models automatically serialize to their UUIDs */
+            /* courtesy of the model toJSON */
         },
     }
 });

IPython/html/static/widgets/js/widget.js

@@ -1,816 +1,824
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define(["widgets/js/manager",
         "underscore",
         "backbone",
         "jquery",
         "base/js/utils",
         "base/js/namespace",
 ], function(widgetmanager, _, Backbone, $, utils, IPython){
     "use strict";
 
     var WidgetModel = Backbone.Model.extend({
         constructor: function (widget_manager, model_id, comm) {
             /**
              * Constructor
              *
              * Creates a WidgetModel instance.
              *
              * Parameters
              * ----------
              * widget_manager : WidgetManager instance
              * model_id : string
              *      An ID unique to this model.
              * comm : Comm instance (optional)
              */
             this.widget_manager = widget_manager;
             this.state_change = Promise.resolve();
             this._buffered_state_diff = {};
             this.pending_msgs = 0;
             this.msg_buffer = null;
             this.state_lock = null;
             this.id = model_id;
             this.views = {};
             this.serializers = {};
             this._resolve_received_state = {};
 
             if (comm !== undefined) {
                 // Remember comm associated with the model.
                 this.comm = comm;
                 comm.model = this;
 
                 // Hook comm messages up to model.
                 comm.on_close($.proxy(this._handle_comm_closed, this));
                 comm.on_msg($.proxy(this._handle_comm_msg, this));
 
                 // Assume the comm is alive.
                 this.set_comm_live(true);
             } else {
                 this.set_comm_live(false);
             }
 
             // Listen for the events that lead to the websocket being terminated.
             var that = this;
             var died = function() {
                 that.set_comm_live(false);
             };
             widget_manager.notebook.events.on('kernel_disconnected.Kernel', died);
             widget_manager.notebook.events.on('kernel_killed.Kernel', died);
             widget_manager.notebook.events.on('kernel_restarting.Kernel', died);
             widget_manager.notebook.events.on('kernel_dead.Kernel', died);
 
             return Backbone.Model.apply(this);
         },
 
         send: function (content, callbacks, buffers) {
             /**
              * Send a custom msg over the comm.
              */
             if (this.comm !== undefined) {
                 var data = {method: 'custom', content: content};
                 this.comm.send(data, callbacks, {}, buffers);
                 this.pending_msgs++;
             }
         },
 
         request_state: function(callbacks) {
             /** 
              * Request a state push from the back-end.
              */
             if (!this.comm) {
                 console.error("Could not request_state because comm doesn't exist!");
                 return;
             }
 
             var msg_id = this.comm.send({method: 'request_state'}, callbacks || this.widget_manager.callbacks());
 
             // Promise that is resolved when a state is received
             // from the back-end.
             var that = this;
             var received_state = new Promise(function(resolve) {
                 that._resolve_received_state[msg_id] = resolve;
             });
             return received_state;
         },
 
         set_comm_live: function(live) {
             /** 
              * Change the comm_live state of the model.
              */
             if (this.comm_live === undefined || this.comm_live != live) {
                 this.comm_live = live;
                 this.trigger(live ? 'comm:live' : 'comm:dead', {model: this});
             }
         },
 
         close: function(comm_closed) {
             /**
              * Close model
              */
             if (this.comm && !comm_closed) {
                 this.comm.close();
             }
             this.stopListening();
             this.trigger('destroy', this);
             delete this.comm.model; // Delete ref so GC will collect widget model.
             delete this.comm;
             delete this.model_id; // Delete id from model so widget manager cleans up.
             _.each(this.views, function(v, id, views) {
                 v.then(function(view) {
                     view.remove();
                     delete views[id];
                 });
             });
         },
 
         _handle_comm_closed: function (msg) {
             /** 
              * Handle when a widget is closed.
              */
             this.trigger('comm:close');
             this.close(true);
         },
 
         _handle_comm_msg: function (msg) {
             /**
              * Handle incoming comm msg.
              */
             var method = msg.content.data.method;
             
             var that = this;
             switch (method) {
                 case 'update':
                     this.state_change = this.state_change
                         .then(function() {
                             var state = msg.content.data.state || {};
                             var buffer_keys = msg.content.data.buffers || [];
                             var buffers = msg.buffers || [];
                             var metadata = msg.content.data.metadata || {};
                             var i,k;
                             for (var i=0; i<buffer_keys.length; i++) {
                                 k = buffer_keys[i];
                                 state[k] = buffers[i];
                             }
 
                             // for any metadata specifying a deserializer, set the
                             // state to a promise that resolves to the deserialized version
                             // also, store the serialization function for the attribute
                             var keys = Object.keys(metadata);
                             for (var i=0; i<keys.length; i++) {
                                 k = keys[i];
                                 if (metadata[k] && metadata[k].serialization) {
                                     that.serializers[k] = utils.load_class.apply(that,
                                                                                  metadata[k].serialization);
                                     state[k] = that.deserialize(that.serializers[k], state[k]);
                                 }
                             }
                             return utils.resolve_promises_dict(state);
                         }).then(function(state) {
                             return that.set_state(state);
                         }).catch(utils.reject("Couldn't process update msg for model id '" + String(that.id) + "'", true))
                         .then(function() {
                             var parent_id = msg.parent_header.msg_id;
                             if (that._resolve_received_state[parent_id] !== undefined) {
                                 that._resolve_received_state[parent_id].call();
                                 delete that._resolve_received_state[parent_id];
                             }
                         }).catch(utils.reject("Couldn't resolve state request promise", true));
                     break;
                 case 'custom':
                     this.trigger('msg:custom', msg.content.data.content, msg.buffers);
                     break;
                 case 'display':
                     this.state_change = this.state_change.then(function() {
                         that.widget_manager.display_view(msg, that);
                     }).catch(utils.reject('Could not process display view msg', true));
                     break;
             }
         },
 
         deserialize: function(serializer, value) {
             // given a serializer dict and a value,
             // return a promise for the deserialized value
             var that = this;
             return serializer.then(function(s) {
                 if (s.deserialize) {
                     return s.deserialize(value, that);
                 } else {
                     return value;
                 }
             });
         },
 
         set_state: function (state) {
             var that = this;
             // Handle when a widget is updated via the python side.
             return new Promise(function(resolve, reject) {
                 that.state_lock = state;
                 try {
                     WidgetModel.__super__.set.call(that, state);
                 } finally {
                     that.state_lock = null;
                 }
                 resolve();
             }).catch(utils.reject("Couldn't set model state", true));
         },
 
         get_state: function() {
             // Get the serializable state of the model.
             // Equivalent to Backbone.Model.toJSON()
             return _.clone(this.attributes);
         },
         
         _handle_status: function (msg, callbacks) {
             /**
              * Handle status msgs.
              *
              * execution_state : ('busy', 'idle', 'starting')
              */
             if (this.comm !== undefined) {
                 if (msg.content.execution_state ==='idle') {
                     // Send buffer if this message caused another message to be
                     // throttled.
                     if (this.msg_buffer !== null &&
                         (this.get('msg_throttle') || 3) === this.pending_msgs) {
                         var data = {method: 'backbone', sync_method: 'update', sync_data: this.msg_buffer};
                         this.comm.send(data, callbacks);
                         this.msg_buffer = null;
                     } else {
                         --this.pending_msgs;
                     }
                 }
             }
         },
 
         callbacks: function(view) {
             /**
              * Create msg callbacks for a comm msg.
              */
             var callbacks = this.widget_manager.callbacks(view);
 
             if (callbacks.iopub === undefined) {
                 callbacks.iopub = {};
             }
 
             var that = this;
             callbacks.iopub.status = function (msg) {
                 that._handle_status(msg, callbacks);
             };
             return callbacks;
         },
 
         set: function(key, val, options) {
             /**
              * Set a value.
              */
             var return_value = WidgetModel.__super__.set.apply(this, arguments);
 
             // Backbone only remembers the diff of the most recent set()
             // operation.  Calling set multiple times in a row results in a 
             // loss of diff information.  Here we keep our own running diff.
             this._buffered_state_diff = $.extend(this._buffered_state_diff, this.changedAttributes() || {});
             return return_value;
         },
 
         sync: function (method, model, options) {
             /**
              * Handle sync to the back-end.  Called when a model.save() is called.
              *
              * Make sure a comm exists.
 
              * Parameters
              * ----------
              * method : create, update, patch, delete, read
              *   create/update always send the full attribute set
              *   patch - only send attributes listed in options.attrs, and if we are queuing
              *     up messages, combine with previous messages that have not been sent yet
              * model : the model we are syncing
              *   will normally be the same as `this`
              * options : dict
              *   the `attrs` key, if it exists, gives an {attr: value} dict that should be synced,
              *   otherwise, sync all attributes
              * 
              */
             var error = options.error || function() {
                 console.error('Backbone sync error:', arguments);
             };
             if (this.comm === undefined) {
                 error();
                 return false;
             }
 
             var attrs = (method === 'patch') ? options.attrs : model.get_state(options);
 
             // the state_lock lists attributes that are currently be changed right now from a kernel message
             // we don't want to send these non-changes back to the kernel, so we delete them out of attrs
             // (but we only delete them if the value hasn't changed from the value stored in the state_lock
             if (this.state_lock !== null) {
                 var keys = Object.keys(this.state_lock);
                 for (var i=0; i<keys.length; i++) {
                     var key = keys[i];
                     if (attrs[key] === this.state_lock[key]) {
                         delete attrs[key];
                     }
                 }
             }
             
             if (_.size(attrs) > 0) {
 
                 // If this message was sent via backbone itself, it will not
                 // have any callbacks.  It's important that we create callbacks
                 // so we can listen for status messages, etc...
                 var callbacks = options.callbacks || this.callbacks();
 
                 // Check throttle.
                 if (this.pending_msgs >= (this.get('msg_throttle') || 3)) {
                     // The throttle has been exceeded, buffer the current msg so
                     // it can be sent once the kernel has finished processing 
                     // some of the existing messages.
                     
                     // Combine updates if it is a 'patch' sync, otherwise replace updates
                     switch (method) {
                         case 'patch':
                             this.msg_buffer = $.extend(this.msg_buffer || {}, attrs);
                             break;
                         case 'update':
                         case 'create':
                             this.msg_buffer = attrs;
                             break;
                         default:
                             error();
                             return false;
                     }
                     this.msg_buffer_callbacks = callbacks;
 
                 } else {
                     // We haven't exceeded the throttle, send the message like 
                     // normal.
                     this.send_sync_message(attrs, callbacks);
                     this.pending_msgs++;
                 }
             }
             // Since the comm is a one-way communication, assume the message 
             // arrived.  Don't call success since we don't have a model back from the server
             // this means we miss out on the 'sync' event.
             this._buffered_state_diff = {};
         },
 
 
         send_sync_message: function(attrs, callbacks) {
             // prepare and send a comm message syncing attrs
             var that = this;
             // first, build a state dictionary with key=the attribute and the value
             // being the value or the promise of the serialized value
             var state_promise_dict = {};
             var keys = Object.keys(attrs);
             for (var i=0; i<keys.length; i++) {
                 // bind k and v locally; needed since we have an inner async function using v
                 (function(k,v) {
                     if (that.serializers[k]) {
                         state_promise_dict[k] = that.serializers[k].then(function(f) {
                             if (f.serialize) {
                                 return f.serialize(v, that);
                             } else {
                                 return v;
                             }
                         })
                     } else {
                         state_promise_dict[k] = v;
                     }
                 })(keys[i], attrs[keys[i]])
             }
             utils.resolve_promises_dict(state_promise_dict).then(function(state) {
                 // get binary values, then send
                 var keys = Object.keys(state);
                 var buffers = [];
                 var buffer_keys = [];
                 for (var i=0; i<keys.length; i++) {
                     var key = keys[i];
                     var value = state[key];
                     if (value.buffer instanceof ArrayBuffer
                         || value instanceof ArrayBuffer) {
                         buffers.push(value);
                         buffer_keys.push(key);
                         delete state[key];
                     }
                 }
                 that.comm.send({method: 'backbone', sync_data: state, buffer_keys: buffer_keys}, callbacks, {}, buffers);
             }).catch(function(error) {
                 that.pending_msgs--;
                 return (utils.reject("Couldn't send widget sync message", true))(error);
             });
         },
         
         serialize: function(model, attrs) {
             // Serialize the attributes into a sync message
             var keys = Object.keys(attrs);            
             var key, value;
             var buffers, metadata, buffer_keys, serialize;
             for (var i=0; i<keys.length; i++) {
                 key = keys[i];
                 serialize = model.serializers[key];
                 if (serialize && serialize.serialize) {
                     attrs[key] = serialize.serialize(attrs[key]);
                 }
             }
         },
 
         save_changes: function(callbacks) {
             /**
              * Push this model's state to the back-end
              *
              * This invokes a Backbone.Sync.
              */
             this.save(this._buffered_state_diff, {patch: true, callbacks: callbacks});
         },
 
         on_some_change: function(keys, callback, context) {
             /**
              * on_some_change(["key1", "key2"], foo, context) differs from
              * on("change:key1 change:key2", foo, context).
              * If the widget attributes key1 and key2 are both modified, 
              * the second form will result in foo being called twice
              * while the first will call foo only once.
              */
             this.on('change', function() {
                 if (keys.some(this.hasChanged, this)) {
                     callback.apply(context);
                 }
             }, this);
 
         },
+
+        toJSON: function(options) {
+            /**
+             * Serialize the model.  See the types.js deserialization function
+             * and the kernel-side serializer/deserializer
+             */
+            return "IPY_MODEL_"+this.id;
+        }
     });
     widgetmanager.WidgetManager.register_widget_model('WidgetModel', WidgetModel);
 
 
     var WidgetView = Backbone.View.extend({
         initialize: function(parameters) {
             /**
              * Public constructor.
              */
             this.model.on('change',this.update,this);
 
             // Bubble the comm live events.
             this.model.on('comm:live', function() {
                 this.trigger('comm:live', this);
             }, this);
             this.model.on('comm:dead', function() {
                 this.trigger('comm:dead', this);
             }, this);
 
             this.options = parameters.options;
             this.on('displayed', function() { 
                 this.is_displayed = true; 
             }, this);
         },
 
         update: function(){
             /**
              * Triggered on model change.
              *
              * Update view to be consistent with this.model
              */
         },
 
         create_child_view: function(child_model, options) {
             /**
              * Create and promise that resolves to a child view of a given model
              */
             var that = this;
             options = $.extend({ parent: this }, options || {});
             return this.model.widget_manager.create_view(child_model, options).catch(utils.reject("Couldn't create child view", true));
         },
 
         callbacks: function(){
             /**
              * Create msg callbacks for a comm msg.
              */
             return this.model.callbacks(this);
         },
 
         render: function(){
             /**
              * Render the view.
              *
              * By default, this is only called the first time the view is created
              */
         },
 
         send: function (content, buffers) {
             /**
              * Send a custom msg associated with this view.
              */
             this.model.send(content, this.callbacks(), buffers);
         },
 
         touch: function () {
             this.model.save_changes(this.callbacks());
         },
 
         after_displayed: function (callback, context) {
             /**
              * Calls the callback right away is the view is already displayed
              * otherwise, register the callback to the 'displayed' event.
              */
             if (this.is_displayed) {
                 callback.apply(context);
             } else {
                 this.on('displayed', callback, context);
             }
         },
 
         remove: function () {
             // Raise a remove event when the view is removed.
             WidgetView.__super__.remove.apply(this, arguments);
             this.trigger('remove');
         }
     });
 
 
     var DOMWidgetView = WidgetView.extend({
         initialize: function (parameters) {
             /**
              * Public constructor
              */
             DOMWidgetView.__super__.initialize.apply(this, [parameters]);
             this.model.on('change:visible', this.update_visible, this);
             this.model.on('change:_css', this.update_css, this);
 
             this.model.on('change:_dom_classes', function(model, new_classes) {
                 var old_classes = model.previous('_dom_classes');
                 this.update_classes(old_classes, new_classes);
             }, this);
 
             this.model.on('change:color', function (model, value) { 
                 this.update_attr('color', value); }, this);
 
             this.model.on('change:background_color', function (model, value) { 
                 this.update_attr('background', value); }, this);
 
             this.model.on('change:width', function (model, value) { 
                 this.update_attr('width', value); }, this);
 
             this.model.on('change:height', function (model, value) { 
                 this.update_attr('height', value); }, this);
 
             this.model.on('change:border_color', function (model, value) { 
                 this.update_attr('border-color', value); }, this);
 
             this.model.on('change:border_width', function (model, value) { 
                 this.update_attr('border-width', value); }, this);
 
             this.model.on('change:border_style', function (model, value) { 
                 this.update_attr('border-style', value); }, this);
 
             this.model.on('change:font_style', function (model, value) { 
                 this.update_attr('font-style', value); }, this);
 
             this.model.on('change:font_weight', function (model, value) { 
                 this.update_attr('font-weight', value); }, this);
 
             this.model.on('change:font_size', function (model, value) { 
                 this.update_attr('font-size', this._default_px(value)); }, this);
 
             this.model.on('change:font_family', function (model, value) { 
                 this.update_attr('font-family', value); }, this);
 
             this.model.on('change:padding', function (model, value) { 
                 this.update_attr('padding', value); }, this);
 
             this.model.on('change:margin', function (model, value) { 
                 this.update_attr('margin', this._default_px(value)); }, this);
 
             this.model.on('change:border_radius', function (model, value) { 
                 this.update_attr('border-radius', this._default_px(value)); }, this);
 
             this.after_displayed(function() {
                 this.update_visible(this.model, this.model.get("visible"));
                 this.update_classes([], this.model.get('_dom_classes'));
                 
                 this.update_attr('color', this.model.get('color'));
                 this.update_attr('background', this.model.get('background_color'));
                 this.update_attr('width', this.model.get('width'));
                 this.update_attr('height', this.model.get('height'));
                 this.update_attr('border-color', this.model.get('border_color'));
                 this.update_attr('border-width', this.model.get('border_width'));
                 this.update_attr('border-style', this.model.get('border_style'));
                 this.update_attr('font-style', this.model.get('font_style'));
                 this.update_attr('font-weight', this.model.get('font_weight'));
                 this.update_attr('font-size', this._default_px(this.model.get('font_size')));
                 this.update_attr('font-family', this.model.get('font_family'));
                 this.update_attr('padding', this.model.get('padding'));
                 this.update_attr('margin', this._default_px(this.model.get('margin')));
                 this.update_attr('border-radius', this._default_px(this.model.get('border_radius')));
 
                 this.update_css(this.model, this.model.get("_css"));
             }, this);
         },
 
         _default_px: function(value) {
             /**
              * Makes browser interpret a numerical string as a pixel value.
              */
             if (value && /^\d+\.?(\d+)?$/.test(value.trim())) {
                 return value.trim() + 'px';
             }
             return value;
         },
 
         update_attr: function(name, value) {
             /**
              * Set a css attr of the widget view.
              */
             this.$el.css(name, value);
         },
 
         update_visible: function(model, value) {
             /**
              * Update visibility
              */
             switch(value) {
                 case null: // python None
                     this.$el.show().css('visibility', 'hidden'); break;
                 case false:
                     this.$el.hide(); break;
                 case true:
                     this.$el.show().css('visibility', ''); break;
             }
          },
 
         update_css: function (model, css) {
             /**
              * Update the css styling of this view.
              */
             if (css === undefined) {return;}
             for (var i = 0; i < css.length; i++) {
                 // Apply the css traits to all elements that match the selector.
                 var selector = css[i][0];
                 var elements = this._get_selector_element(selector);
                 if (elements.length > 0) {
                     var trait_key = css[i][1];
                     var trait_value = css[i][2];
                     elements.css(trait_key ,trait_value);
                 }
             }
         },
 
         update_classes: function (old_classes, new_classes, $el) {
             /**
              * Update the DOM classes applied to an element, default to this.$el.
              */
             if ($el===undefined) {
                 $el = this.$el;
             }
             _.difference(old_classes, new_classes).map(function(c) {$el.removeClass(c);})
             _.difference(new_classes, old_classes).map(function(c) {$el.addClass(c);})
         },
 
         update_mapped_classes: function(class_map, trait_name, previous_trait_value, $el) {
             /**
              * Update the DOM classes applied to the widget based on a single
              * trait's value.
              *
              * Given a trait value classes map, this function automatically
              * handles applying the appropriate classes to the widget element
              * and removing classes that are no longer valid.
              *
              * Parameters
              * ----------
              * class_map: dictionary
              *  Dictionary of trait values to class lists.
              *  Example:
              *      {
              *          success: ['alert', 'alert-success'],
              *          info: ['alert', 'alert-info'],
              *          warning: ['alert', 'alert-warning'],
              *          danger: ['alert', 'alert-danger']
              *      };
              * trait_name: string
              *  Name of the trait to check the value of.
              * previous_trait_value: optional string, default ''
              *  Last trait value
              * $el: optional jQuery element handle, defaults to this.$el
              *  Element that the classes are applied to.
              */
             var key = previous_trait_value;
             if (key === undefined) {
                 key = this.model.previous(trait_name);
             }
             var old_classes = class_map[key] ? class_map[key] : [];
             key = this.model.get(trait_name);
             var new_classes = class_map[key] ? class_map[key] : [];
 
             this.update_classes(old_classes, new_classes, $el || this.$el);
         },
         
         _get_selector_element: function (selector) {
             /**
              * Get the elements via the css selector.
              */
             var elements;
             if (!selector) {
                 elements = this.$el;
             } else {
                 elements = this.$el.find(selector).addBack(selector);
             }
             return elements;
         },
 
         typeset: function(element, text){
             utils.typeset.apply(null, arguments);
         },
     });
 
 
     var ViewList = function(create_view, remove_view, context) {
         /**
          * - create_view and remove_view are default functions called when adding or removing views
          * - create_view takes a model and returns a view or a promise for a view for that model
          * - remove_view takes a view and destroys it (including calling `view.remove()`)
          * - each time the update() function is called with a new list, the create and remove
          *   callbacks will be called in an order so that if you append the views created in the
          *   create callback and remove the views in the remove callback, you will duplicate 
          *   the order of the list.
          * - the remove callback defaults to just removing the view (e.g., pass in null for the second parameter)
          * - the context defaults to the created ViewList.  If you pass another context, the create and remove
          *   will be called in that context.
          */
 
         this.initialize.apply(this, arguments);
     };
 
     _.extend(ViewList.prototype, {
         initialize: function(create_view, remove_view, context) {
             this._handler_context = context || this;
             this._models = [];
             this.views = []; // list of promises for views
             this._create_view = create_view;
             this._remove_view = remove_view || function(view) {view.remove();};
         },
 
         update: function(new_models, create_view, remove_view, context) {
             /**
              * the create_view, remove_view, and context arguments override the defaults
              * specified when the list is created.
              * after this function, the .views attribute is a list of promises for views
              * if you want to perform some action on the list of views, do something like
              * `Promise.all(myviewlist.views).then(function(views) {...});`
              */
             var remove = remove_view || this._remove_view;
             var create = create_view || this._create_view;
             context = context || this._handler_context;
             var i = 0;
             // first, skip past the beginning of the lists if they are identical
             for (; i < new_models.length; i++) {
                 if (i >= this._models.length || new_models[i] !== this._models[i]) {
                     break;
                 }
             }
             
             var first_removed = i;
             // Remove the non-matching items from the old list.
             var removed = this.views.splice(first_removed, this.views.length-first_removed);
             for (var j = 0; j < removed.length; j++) {
                 removed[j].then(function(view) {
                     remove.call(context, view)
                 });
             }
 
             // Add the rest of the new list items.
             for (; i < new_models.length; i++) {
                 this.views.push(Promise.resolve(create.call(context, new_models[i])));
             }
             // make a copy of the input array
             this._models = new_models.slice();
         },
 
         remove: function() {
             /**
              * removes every view in the list; convenience function for `.update([])`
              * that should be faster
              * returns a promise that resolves after this removal is done
              */
             var that = this;
             return Promise.all(this.views).then(function(views) {
                 for (var i = 0; i < that.views.length; i++) {
                     that._remove_view.call(that._handler_context, views[i]);
                 }
                 that.views = [];
                 that._models = [];
             });
         },
     });
 
     var widget = {
         'WidgetModel': WidgetModel,
         'WidgetView': WidgetView,
         'DOMWidgetView': DOMWidgetView,
         'ViewList': ViewList,
     };
 
     // For backwards compatability.
     $.extend(IPython, widget);
 
     return widget;
 });