widget.js

// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.
'use strict';

var utils = require('./utils');
var managerBase = require('./manager-base');
var _ = require('underscore');
var Backbone = require('backbone');


var unpack_models = function unpack_models(value, manager) {
    /**
     * Replace model ids with models recursively.
     */
    var unpacked;
    if (_.isArray(value)) {
        unpacked = [];
        _.each(value, function(sub_value, key) {
            unpacked.push(unpack_models(sub_value, manager));
        });
        return Promise.all(unpacked);
    } else if (value instanceof Object) {
        unpacked = {};
        _.each(value, function(sub_value, key) {
            unpacked[key] = unpack_models(sub_value, manager);
        });
        return utils.resolvePromisesDict(unpacked);
    } else if (typeof value === 'string' && value.slice(0,10) === 'IPY_MODEL_') {
        // get_model returns a promise already
        return manager.get_model(value.slice(10, value.length));
    } else {
        return Promise.resolve(value);
    }
};

var WidgetModel = Backbone.Model.extend({

    defaults: {
        _model_module: "jupyter-js-widgets",
        _model_name: "WidgetModel",
        _view_module: "jupyter-js-widgets",
        _view_name: null,
        msg_throttle: 3
    },

    constructor: function (widget_manager, model_id, comm, attributes) {
        /**
         * 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;

        // Force backbone to think that the model has already been
        // synced with the server.  As of backbone 1.1, backbone
        // ignores `patch` if it thinks the model has never been
        // pushed.
        this.isNew = function() { return false; };

        this.views = {};

        if (comm) {
            // Remember comm associated with the model.
            this.comm = comm;
            comm.model = this;

            // Hook comm messages up to model.
            comm.on_close(_.bind(this._handle_comm_closed, this));
            comm.on_msg(_.bind(this._handle_comm_msg, this));

            this.comm_live = true;
        } else {
            this.comm_live = false;
        }

        WidgetModel.__super__.constructor.apply(this, [attributes]);
    },

    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++;
        }
    },

    close: function(comm_closed) {
        /**
         * Close model
         */
        if (this.comm && !comm_closed) {
            this.comm.close();
        }
        this.stopListening();
        this.trigger('destroy', this);
        if (this.comm) {
            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 || [];
                        for (var i=0; i<buffer_keys.length; i++) {
                            state[buffer_keys[i]] = buffers[i];
                        }
                        return that.constructor._deserialize_state(state, that.widget_manager);
                    }).then(function(state) {
                        that.set_state(state);
                    }).catch(utils.reject('Could not process update msg for model id: ' + String(that.id), true))
                return this.state_change;
            case 'custom':
                this.trigger('msg:custom', msg.content.data.content, msg.buffers);
                return Promise.resolve();
            case 'display':
                this.state_change = this.state_change.then(function() {
                    that.widget_manager.display_model(msg, that);
                }).catch(utils.reject('Could not process display view msg', true));
                return this.state_change;
        }
    },

    set_state: function (state) {
        // Handles when a widget is updated from the backend.
        this.state_lock = state;
        try {
            this.set(state);
            this.state_lock = null;
        } catch(e) {
            console.error('Error setting state:', e.message);
        }
    },

    get_state: function(drop_defaults) {
        /**
         * Get the serializable state of the model.
         *
         * If drop_default is thruthy, attributes that are equal to their default
         * values are dropped.
         */
        var state = this.attributes;
        if (drop_defaults) {
            var defaults = _.result(this, 'defaults');
            return Object.keys(state).reduce(function(obj, key) {
                if (!_.isEqual(state[key], defaults[key])) {
                    obj[key] = state[key];
                }
                return obj;
            }, {});
        } else {
            return _.clone(state);
        }
    },

    _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') || 1) === 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.
        //
        // However, we don't buffer the initial state comming from the
        // backend or the default values specified in `defaults`.
        //
        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 being 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') || 1)) {
                // 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 serializers = this.constructor.serializers;
        if (serializers) {
            for (var k in attrs) {
                if (serializers[k] && serializers[k].serialize) {
                    attrs[k] = (serializers[k].serialize)(attrs[k], this);
                }
            }
        }
        utils.resolvePromisesDict(attrs).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) {
                    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('Could not send widget sync message', true))(error);
        });
    },

    save_changes: function(callbacks) {
        /**
         * Push this model's state to the back-end
         *
         * This invokes a Backbone.Sync.
         */
        if (this.comm_live) {
            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, arguments);
            }
        }, this);
    },

    toJSON: function(options) {
        /**
         * Serialize the model.  See the deserialization function at the top of this file
         * and the kernel-side serializer/deserializer.
         */
        return 'IPY_MODEL_' + this.id;
    }
}, {
    _deserialize_state: function(state, manager) {
        /**
         * Returns a promise for the deserialized state. The second argument
         * is an instance of widget manager, which is required for the
         * deserialization of widget models.
         */
        var serializers = this.serializers;
        var deserialized;
        if (serializers) {
            deserialized = {};
            for (var k in state) {
                if (serializers[k] && serializers[k].deserialize) {
                     deserialized[k] = (serializers[k].deserialize)(state[k], manager);
                } else {
                     deserialized[k] = state[k];
                }
            }
        } else {
            deserialized = state;
        }
        return utils.resolvePromisesDict(deserialized);
    },

    _serialize_state: function(state, manager) {
        /**
         * Returns a promise for the serialized state. The second argument
         * is an instance of widget manager.
         */
        var serializers = this.serializers;
        var serialized;
        if (serializers) {
            serialized = {};
            for (var k in state) {
                if (serializers[k] && serializers[k].serialize) {
                     serialized[k] = (serializers[k].serialize)(state[k], manager);
                } else {
                     serialized[k] = state[k];
                }
            }
        } else {
            serialized = state;
        }
        return utils.resolvePromisesDict(serialized);
    }
});


var WidgetViewMixin = {
    initialize: function(parameters) {
        /**
         * Public constructor.
         */
        this.listenTo(this.model, 'change', this.update, this);

        this.options = parameters.options;
        /**
         * this.displayed is a promise that resolves when the view is
         * inserted in the DOM.
         */
        var that = this;
        this.displayed = new Promise(function(resolve, reject) {
            that.once('displayed', resolve);
        });
    },

    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('Could not 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());
    },

    remove: function () {
        // Raise a remove event when the view is removed.
        WidgetView.__super__.remove.apply(this, arguments);
        this.trigger('remove');
    }
};

var DOMWidgetModel = WidgetModel.extend({
    defaults: _.extend({}, WidgetModel.prototype.defaults, {
        layout: undefined,
        visible: true,
        _dom_classes: [],

        // Deprecated attributes
        color: null,
        height: '',
        border_radius: '',
        border_width: '',
        background_color: null,
        font_style: '',
        width: '',
        font_family: '',
        border_color: null,
        padding: '',
        font_weight: '',
        icon: '',
        border_style: '',
        font_size: '',
        margin: ''
    }),
}, {
    serializers: _.extend({
        layout: {deserialize: unpack_models},
    }, WidgetModel.serializers)
});

var DOMWidgetViewMixin = {
    initialize: function (parameters) {
        /**
         * Public constructor
         */
        WidgetViewMixin.initialize.apply(this, [parameters]);
        this.id = utils.uuid();

        this.listenTo(this.model, 'change:visible', this.update_visible, this); // TODO: Deprecated in 5.0

        this.listenTo(this.model, 'change:_dom_classes', function(model, new_classes) {
            var old_classes = model.previous('_dom_classes');
            this.update_classes(old_classes, new_classes);
        }, this);

        this.listenTo(this.model, 'change:color', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('color', value); }, this);

        this.listenTo(this.model, 'change:background_color', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('background', value); }, this);

        this.listenTo(this.model, 'change:width', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('width', this._default_px(value)); }, this);

        this.listenTo(this.model, 'change:height', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('height', this._default_px(value)); }, this);

        this.listenTo(this.model, 'change:border_color', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('border-color', value); }, this);

        this.listenTo(this.model, 'change:border_width', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('border-width', this._default_px(value)); }, this);

        this.listenTo(this.model, 'change:border_style', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('border-style', value); }, this);

        this.listenTo(this.model, 'change:font_style', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('font-style', value); }, this);

        this.listenTo(this.model, 'change:font_weight', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('font-weight', value); }, this);

        this.listenTo(this.model, 'change:font_size', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('font-size', this._default_px(value)); }, this);

        this.listenTo(this.model, 'change:font_family', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('font-family', value); }, this);

        this.listenTo(this.model, 'change:padding', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('padding', this._default_px(value)); }, this);

        this.listenTo(this.model, 'change:margin', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('margin', this._default_px(value)); }, this);

        this.listenTo(this.model, 'change:border_radius', function (model, value) { // TODO: Deprecated in 5.0
            this.update_attr('border-radius', this._default_px(value)); }, this);

        this.layoutPromise = Promise.resolve();
        this.listenTo(this.model, 'change:layout', function(model, value) {
            this.setLayout(value, model.previous('layout'));
        });

        this.displayed.then(_.bind(function() {
            this.update_visible(this.model, this.model.get('visible')); // TODO: Deprecated in 5.0
            this.update_classes([], this.model.get('_dom_classes'));

            this.update_attr('color', this.model.get('color')); // TODO: Deprecated in 5.0
            this.update_attr('background', this.model.get('background_color')); // TODO: Deprecated in 5.0
            this.update_attr('width', this._default_px(this.model.get('width'))); // TODO: Deprecated in 5.0
            this.update_attr('height', this._default_px(this.model.get('height'))); // TODO: Deprecated in 5.0
            this.update_attr('border-color', this.model.get('border_color')); // TODO: Deprecated in 5.0
            this.update_attr('border-width', this._default_px(this.model.get('border_width'))); // TODO: Deprecated in 5.0
            this.update_attr('border-style', this.model.get('border_style')); // TODO: Deprecated in 5.0
            this.update_attr('font-style', this.model.get('font_style')); // TODO: Deprecated in 5.0
            this.update_attr('font-weight', this.model.get('font_weight')); // TODO: Deprecated in 5.0
            this.update_attr('font-size', this._default_px(this.model.get('font_size'))); // TODO: Deprecated in 5.0
            this.update_attr('font-family', this.model.get('font_family')); // TODO: Deprecated in 5.0
            this.update_attr('padding', this._default_px(this.model.get('padding'))); // TODO: Deprecated in 5.0
            this.update_attr('margin', this._default_px(this.model.get('margin'))); // TODO: Deprecated in 5.0
            this.update_attr('border-radius', this._default_px(this.model.get('border_radius'))); // TODO: Deprecated in 5.0

            this.setLayout(this.model.get('layout'));
        }, this));
    },

    setLayout: function(layout, oldLayout) {
        var that = this;
        if (layout) {
            this.layoutPromise = this.layoutPromise.then(function(oldLayoutView) {
                if (oldLayoutView) {
                    oldLayoutView.unlayout();
                }

                return that.create_child_view(layout).then(function(view) {

                    // Trigger the displayed event of the child view.
                    return that.displayed.then(function() {
                        view.trigger('displayed', that);
                        return view;
                    });
                }).catch(utils.reject('Could not add LayoutView to DOMWidgetView', true));
            });
        }
    },

    _default_px: function(value) { // TODO: Deprecated in 5.0
        /**
         * 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) { // TODO: Deprecated in 5.0
        /**
         * Set a css attr of the widget view.
         */
        this.el.style[name] = value;
    },

    update_visible: function(model, value) { // TODO: Deprecated in 5.0
        /**
         * Update visibility
         */
        switch(value) {
            case null:
                if (this._old_display !== undefined) {
                    this.el.style.display = this._old_display;
                }
                this.el.style.visibility = 'hidden'; break;
            case false:
                this._old_display = this.el.style.display || '';
                this.el.style.display = 'none'; break;
            case true:
                if (this._old_display !== undefined) {
                    this.el.style.display = this._old_display;
                }
                this.el.style.visibility = ''; break;
        }
    },

    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) {
            if (el.classList) { // classList is not supported by IE for svg elements
                el.classList.remove(c);
            } else {
                el.setAttribute('class', el.getAttribute('class').replace(c, ''));
            }
        });
        _.difference(new_classes, old_classes).map(function(c) {
            if (el.classList) { // classList is not supported by IE for svg elements
                el.classList.add(c);
            } else {
                el.setAttribute('class', el.getAttribute('class').concat(' ', c));
            }
        });
    },

    update_mapped_classes: function(class_map, trait_name, 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.
         * el: optional DOM element handle, defaults to this.$el
         *  Element that the classes are applied to.
         */
        var 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);
    },

    typeset: function(element, text){
        utils.typeset(element, text);
    }
};


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 = [];
        });
    }
});

// For backwards compatibility.
var WidgetView = Backbone.View.extend(WidgetViewMixin);
var DOMWidgetView = WidgetView.extend(DOMWidgetViewMixin);

var widget = {
    unpack_models: unpack_models,
    WidgetModel: WidgetModel,
    WidgetViewMixin: WidgetViewMixin,
    DOMWidgetViewMixin: DOMWidgetViewMixin,
    ViewList: ViewList,
    DOMWidgetModel: DOMWidgetModel,

    // For backwards compatibility.
    WidgetView: WidgetView,
    DOMWidgetView: DOMWidgetView
};

module.exports = widget;