Simplify code by using Promises in a better way; try_load -> load

IPython/html/static/base/js/utils.js

@@ -1,672 +1,672 b''
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define([
     'base/js/namespace',
     'jquery',
     'codemirror/lib/codemirror',
 ], function(IPython, $, CodeMirror){
     "use strict";
     
     IPython.load_extensions = function () {
         // load one or more IPython notebook extensions with requirejs
         
         var extensions = [];
         var extension_names = arguments;
         for (var i = 0; i < extension_names.length; i++) {
             extensions.push("nbextensions/" + arguments[i]);
         }
         
         require(extensions,
             function () {
                 for (var i = 0; i < arguments.length; i++) {
                     var ext = arguments[i];
                     var ext_name = extension_names[i];
                     // success callback
                     console.log("Loaded extension: " + ext_name);
                     if (ext && ext.load_ipython_extension !== undefined) {
                         ext.load_ipython_extension();
                     }
                 }
             },
             function (err) {
                 // failure callback
                 console.log("Failed to load extension(s):", err.requireModules, err);
             }
         );
     };
 
     //============================================================================
     // Cross-browser RegEx Split
     //============================================================================
 
     // This code has been MODIFIED from the code licensed below to not replace the
     // default browser split.  The license is reproduced here.
 
     // see http://blog.stevenlevithan.com/archives/cross-browser-split for more info:
     /*!
      * Cross-Browser Split 1.1.1
      * Copyright 2007-2012 Steven Levithan <stevenlevithan.com>
      * Available under the MIT License
      * ECMAScript compliant, uniform cross-browser split method
      */
 
     /**
      * Splits a string into an array of strings using a regex or string
      * separator. Matches of the separator are not included in the result array.
      * However, if `separator` is a regex that contains capturing groups,
      * backreferences are spliced into the result each time `separator` is
      * matched. Fixes browser bugs compared to the native
      * `String.prototype.split` and can be used reliably cross-browser.
      * @param {String} str String to split.
      * @param {RegExp|String} separator Regex or string to use for separating
      *     the string.
      * @param {Number} [limit] Maximum number of items to include in the result
      *     array.
      * @returns {Array} Array of substrings.
      * @example
      *
      * // Basic use
      * regex_split('a b c d', ' ');
      * // -> ['a', 'b', 'c', 'd']
      *
      * // With limit
      * regex_split('a b c d', ' ', 2);
      * // -> ['a', 'b']
      *
      * // Backreferences in result array
      * regex_split('..word1 word2..', /([a-z]+)(\d+)/i);
      * // -> ['..', 'word', '1', ' ', 'word', '2', '..']
      */
     var regex_split = function (str, separator, limit) {
         // If `separator` is not a regex, use `split`
         if (Object.prototype.toString.call(separator) !== "[object RegExp]") {
             return split.call(str, separator, limit);
         }
         var output = [],
             flags = (separator.ignoreCase ? "i" : "") +
                     (separator.multiline  ? "m" : "") +
                     (separator.extended   ? "x" : "") + // Proposed for ES6
                     (separator.sticky     ? "y" : ""), // Firefox 3+
             lastLastIndex = 0,
             // Make `global` and avoid `lastIndex` issues by working with a copy
             separator = new RegExp(separator.source, flags + "g"),
             separator2, match, lastIndex, lastLength;
         str += ""; // Type-convert
 
         var compliantExecNpcg = typeof(/()??/.exec("")[1]) === "undefined";
         if (!compliantExecNpcg) {
             // Doesn't need flags gy, but they don't hurt
             separator2 = new RegExp("^" + separator.source + "$(?!\\s)", flags);
         }
         /* Values for `limit`, per the spec:
          * If undefined: 4294967295 // Math.pow(2, 32) - 1
          * If 0, Infinity, or NaN: 0
          * If positive number: limit = Math.floor(limit); if (limit > 4294967295) limit -= 4294967296;
          * If negative number: 4294967296 - Math.floor(Math.abs(limit))
          * If other: Type-convert, then use the above rules
          */
         limit = typeof(limit) === "undefined" ?
             -1 >>> 0 : // Math.pow(2, 32) - 1
             limit >>> 0; // ToUint32(limit)
         while (match = separator.exec(str)) {
             // `separator.lastIndex` is not reliable cross-browser
             lastIndex = match.index + match[0].length;
             if (lastIndex > lastLastIndex) {
                 output.push(str.slice(lastLastIndex, match.index));
                 // Fix browsers whose `exec` methods don't consistently return `undefined` for
                 // nonparticipating capturing groups
                 if (!compliantExecNpcg && match.length > 1) {
                     match[0].replace(separator2, function () {
                         for (var i = 1; i < arguments.length - 2; i++) {
                             if (typeof(arguments[i]) === "undefined") {
                                 match[i] = undefined;
                             }
                         }
                     });
                 }
                 if (match.length > 1 && match.index < str.length) {
                     Array.prototype.push.apply(output, match.slice(1));
                 }
                 lastLength = match[0].length;
                 lastLastIndex = lastIndex;
                 if (output.length >= limit) {
                     break;
                 }
             }
             if (separator.lastIndex === match.index) {
                 separator.lastIndex++; // Avoid an infinite loop
             }
         }
         if (lastLastIndex === str.length) {
             if (lastLength || !separator.test("")) {
                 output.push("");
             }
         } else {
             output.push(str.slice(lastLastIndex));
         }
         return output.length > limit ? output.slice(0, limit) : output;
     };
 
     //============================================================================
     // End contributed Cross-browser RegEx Split
     //============================================================================
 
 
     var uuid = function () {
         // http://www.ietf.org/rfc/rfc4122.txt
         var s = [];
         var hexDigits = "0123456789ABCDEF";
         for (var i = 0; i < 32; i++) {
             s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
         }
         s[12] = "4";  // bits 12-15 of the time_hi_and_version field to 0010
         s[16] = hexDigits.substr((s[16] & 0x3) | 0x8, 1);  // bits 6-7 of the clock_seq_hi_and_reserved to 01
 
         var uuid = s.join("");
         return uuid;
     };
 
 
     //Fix raw text to parse correctly in crazy XML
     function xmlencode(string) {
         return string.replace(/\&/g,'&'+'amp;')
             .replace(/</g,'&'+'lt;')
             .replace(/>/g,'&'+'gt;')
             .replace(/\'/g,'&'+'apos;')
             .replace(/\"/g,'&'+'quot;')
             .replace(/`/g,'&'+'#96;');
     }
 
 
     //Map from terminal commands to CSS classes
     var ansi_colormap = {
         "01":"ansibold",
         
         "30":"ansiblack",
         "31":"ansired",
         "32":"ansigreen",
         "33":"ansiyellow",
         "34":"ansiblue",
         "35":"ansipurple",
         "36":"ansicyan",
         "37":"ansigray",
         
         "40":"ansibgblack",
         "41":"ansibgred",
         "42":"ansibggreen",
         "43":"ansibgyellow",
         "44":"ansibgblue",
         "45":"ansibgpurple",
         "46":"ansibgcyan",
         "47":"ansibggray"
     };
     
     function _process_numbers(attrs, numbers) {
         // process ansi escapes
         var n = numbers.shift();
         if (ansi_colormap[n]) {
             if ( ! attrs["class"] ) {
                 attrs["class"] = ansi_colormap[n];
             } else {
                 attrs["class"] += " " + ansi_colormap[n];
             }
         } else if (n == "38" || n == "48") {
             // VT100 256 color or 24 bit RGB
             if (numbers.length < 2) {
                 console.log("Not enough fields for VT100 color", numbers);
                 return;
             }
             
             var index_or_rgb = numbers.shift();
             var r,g,b;
             if (index_or_rgb == "5") {
                 // 256 color
                 var idx = parseInt(numbers.shift());
                 if (idx < 16) {
                     // indexed ANSI
                     // ignore bright / non-bright distinction
                     idx = idx % 8;
                     var ansiclass = ansi_colormap[n[0] + (idx % 8).toString()];
                     if ( ! attrs["class"] ) {
                         attrs["class"] = ansiclass;
                     } else {
                         attrs["class"] += " " + ansiclass;
                     }
                     return;
                 } else if (idx < 232) {
                     // 216 color 6x6x6 RGB
                     idx = idx - 16;
                     b = idx % 6;
                     g = Math.floor(idx / 6) % 6;
                     r = Math.floor(idx / 36) % 6;
                     // convert to rgb
                     r = (r * 51);
                     g = (g * 51);
                     b = (b * 51);
                 } else {
                     // grayscale
                     idx = idx - 231;
                     // it's 1-24 and should *not* include black or white,
                     // so a 26 point scale
                     r = g = b = Math.floor(idx * 256 / 26);
                 }
             } else if (index_or_rgb == "2") {
                 // Simple 24 bit RGB
                 if (numbers.length > 3) {
                     console.log("Not enough fields for RGB", numbers);
                     return;
                 }
                 r = numbers.shift();
                 g = numbers.shift();
                 b = numbers.shift();
             } else {
                 console.log("unrecognized control", numbers);
                 return;
             }
             if (r !== undefined) {
                 // apply the rgb color
                 var line;
                 if (n == "38") {
                     line = "color: ";
                 } else {
                     line = "background-color: ";
                 }
                 line = line + "rgb(" + r + "," + g + "," + b + ");";
                 if ( !attrs.style ) {
                     attrs.style = line;
                 } else {
                     attrs.style += " " + line;
                 }
             }
         }
     }
 
     function ansispan(str) {
         // ansispan function adapted from github.com/mmalecki/ansispan (MIT License)
         // regular ansi escapes (using the table above)
         var is_open = false;
         return str.replace(/\033\[(0?[01]|22|39)?([;\d]+)?m/g, function(match, prefix, pattern) {
             if (!pattern) {
                 // [(01|22|39|)m close spans
                 if (is_open) {
                     is_open = false;
                     return "</span>";
                 } else {
                     return "";
                 }
             } else {
                 is_open = true;
 
                 // consume sequence of color escapes
                 var numbers = pattern.match(/\d+/g);
                 var attrs = {};
                 while (numbers.length > 0) {
                     _process_numbers(attrs, numbers);
                 }
 
                 var span = "<span ";
                 for (var attr in attrs) {
                     var value = attrs[attr];
                     span = span + " " + attr + '="' + attrs[attr] + '"';
                 }
                 return span + ">";
             }
         });
     }
 
     // Transform ANSI color escape codes into HTML <span> tags with css
     // classes listed in the above ansi_colormap object. The actual color used
     // are set in the css file.
     function fixConsole(txt) {
         txt = xmlencode(txt);
         var re = /\033\[([\dA-Fa-f;]*?)m/;
         var opened = false;
         var cmds = [];
         var opener = "";
         var closer = "";
 
         // Strip all ANSI codes that are not color related.  Matches
         // all ANSI codes that do not end with "m".
         var ignored_re = /(?=(\033\[[\d;=]*[a-ln-zA-Z]{1}))\1(?!m)/g;
         txt = txt.replace(ignored_re, "");
         
         // color ansi codes
         txt = ansispan(txt);
         return txt;
     }
 
     // Remove chunks that should be overridden by the effect of
     // carriage return characters
     function fixCarriageReturn(txt) {
         var tmp = txt;
         do {
             txt = tmp;
             tmp = txt.replace(/\r+\n/gm, '\n'); // \r followed by \n --> newline
             tmp = tmp.replace(/^.*\r+/gm, '');  // Other \r --> clear line
         } while (tmp.length < txt.length);
         return txt;
     }
 
     // Locate any URLs and convert them to a anchor tag
     function autoLinkUrls(txt) {
         return txt.replace(/(^|\s)(https?|ftp)(:[^'">\s]+)/gi,
             "$1<a target=\"_blank\" href=\"$2$3\">$2$3</a>");
     }
 
     var points_to_pixels = function (points) {
         // A reasonably good way of converting between points and pixels.
         var test = $('<div style="display: none; width: 10000pt; padding:0; border:0;"></div>');
         $(body).append(test);
         var pixel_per_point = test.width()/10000;
         test.remove();
         return Math.floor(points*pixel_per_point);
     };
     
     var always_new = function (constructor) {
         // wrapper around contructor to avoid requiring `var a = new constructor()`
         // useful for passing constructors as callbacks,
         // not for programmer laziness.
         // from http://programmers.stackexchange.com/questions/118798
         return function () {
             var obj = Object.create(constructor.prototype);
             constructor.apply(obj, arguments);
             return obj;
         };
     };
 
     var url_path_join = function () {
         // join a sequence of url components with '/'
         var url = '';
         for (var i = 0; i < arguments.length; i++) {
             if (arguments[i] === '') {
                 continue;
             }
             if (url.length > 0 && url[url.length-1] != '/') {
                 url = url + '/' + arguments[i];
             } else {
                 url = url + arguments[i];
             }
         }
         url = url.replace(/\/\/+/, '/');
         return url;
     };
     
     var url_path_split = function (path) {
         // Like os.path.split for URLs.
         // Always returns two strings, the directory path and the base filename
         
         var idx = path.lastIndexOf('/');
         if (idx === -1) {
             return ['', path];
         } else {
             return [ path.slice(0, idx), path.slice(idx + 1) ];
         }
     };
     
     var parse_url = function (url) {
         // an `a` element with an href allows attr-access to the parsed segments of a URL
         // a = parse_url("http://localhost:8888/path/name#hash")
         // a.protocol = "http:"
         // a.host     = "localhost:8888"
         // a.hostname = "localhost"
         // a.port     = 8888
         // a.pathname = "/path/name"
         // a.hash     = "#hash"
         var a = document.createElement("a");
         a.href = url;
         return a;
     };
     
     var encode_uri_components = function (uri) {
         // encode just the components of a multi-segment uri,
         // leaving '/' separators
         return uri.split('/').map(encodeURIComponent).join('/');
     };
     
     var url_join_encode = function () {
         // join a sequence of url components with '/',
         // encoding each component with encodeURIComponent
         return encode_uri_components(url_path_join.apply(null, arguments));
     };
 
 
     var splitext = function (filename) {
         // mimic Python os.path.splitext
         // Returns ['base', '.ext']
         var idx = filename.lastIndexOf('.');
         if (idx > 0) {
             return [filename.slice(0, idx), filename.slice(idx)];
         } else {
             return [filename, ''];
         }
     };
 
 
     var escape_html = function (text) {
         // escape text to HTML
         return $("<div/>").text(text).html();
     };
 
 
     var get_body_data = function(key) {
         // get a url-encoded item from body.data and decode it
         // we should never have any encoded URLs anywhere else in code
         // until we are building an actual request
         return decodeURIComponent($('body').data(key));
     };
     
     var to_absolute_cursor_pos = function (cm, cursor) {
         // get the absolute cursor position from CodeMirror's col, ch
         if (!cursor) {
             cursor = cm.getCursor();
         }
         var cursor_pos = cursor.ch;
         for (var i = 0; i < cursor.line; i++) {
             cursor_pos += cm.getLine(i).length + 1;
         }
         return cursor_pos;
     };
     
     var from_absolute_cursor_pos = function (cm, cursor_pos) {
         // turn absolute cursor postion into CodeMirror col, ch cursor
         var i, line;
         var offset = 0;
         for (i = 0, line=cm.getLine(i); line !== undefined; i++, line=cm.getLine(i)) {
             if (offset + line.length < cursor_pos) {
                 offset += line.length + 1;
             } else {
                 return {
                     line : i,
                     ch : cursor_pos - offset,
                 };
             }
         }
         // reached end, return endpoint
         return {
             ch : line.length - 1,
             line : i - 1,
         };
     };
     
     // http://stackoverflow.com/questions/2400935/browser-detection-in-javascript
     var browser = (function() {
         if (typeof navigator === 'undefined') {
             // navigator undefined in node
             return 'None';
         }
         var N= navigator.appName, ua= navigator.userAgent, tem;
         var M= ua.match(/(opera|chrome|safari|firefox|msie)\/?\s*(\.?\d+(\.\d+)*)/i);
         if (M && (tem= ua.match(/version\/([\.\d]+)/i)) !== null) M[2]= tem[1];
         M= M? [M[1], M[2]]: [N, navigator.appVersion,'-?'];
         return M;
     })();
 
     // http://stackoverflow.com/questions/11219582/how-to-detect-my-browser-version-and-operating-system-using-javascript
     var platform = (function () {
         if (typeof navigator === 'undefined') {
             // navigator undefined in node
             return 'None';
         }
         var OSName="None";
         if (navigator.appVersion.indexOf("Win")!=-1) OSName="Windows";
         if (navigator.appVersion.indexOf("Mac")!=-1) OSName="MacOS";
         if (navigator.appVersion.indexOf("X11")!=-1) OSName="UNIX";
         if (navigator.appVersion.indexOf("Linux")!=-1) OSName="Linux";
         return OSName;
     })();
 
     var is_or_has = function (a, b) {
         // Is b a child of a or a itself?
         return a.has(b).length !==0 || a.is(b);
     };
 
     var is_focused = function (e) {
         // Is element e, or one of its children focused?
         e = $(e);
         var target = $(document.activeElement);
         if (target.length > 0) {
             if (is_or_has(e, target)) {
                 return true;
             } else {
                 return false;
             }
         } else {
             return false;
         }
     };
     
     var mergeopt = function(_class, options, overwrite){
         options = options || {};
         overwrite = overwrite || {};
         return $.extend(true, {}, _class.options_default, options, overwrite);
     };
     
     var ajax_error_msg = function (jqXHR) {
         // Return a JSON error message if there is one,
         // otherwise the basic HTTP status text.
         if (jqXHR.responseJSON && jqXHR.responseJSON.traceback) {
             return jqXHR.responseJSON.traceback;
         } else if (jqXHR.responseJSON && jqXHR.responseJSON.message) {
             return jqXHR.responseJSON.message;
         } else {
             return jqXHR.statusText;
         }
     };
     var log_ajax_error = function (jqXHR, status, error) {
         // log ajax failures with informative messages
         var msg = "API request failed (" + jqXHR.status + "): ";
         console.log(jqXHR);
         msg += ajax_error_msg(jqXHR);
         console.log(msg);
     };
     
     var requireCodeMirrorMode = function (mode, callback, errback) {
         // load a mode with requirejs
         if (typeof mode != "string") mode = mode.name;
         if (CodeMirror.modes.hasOwnProperty(mode)) {
             callback(CodeMirror.modes.mode);
             return;
         }
         require([
                 // might want to use CodeMirror.modeURL here
                 ['codemirror/mode', mode, mode].join('/'),
             ], callback, errback
         );
     };
     
     /** Error type for wrapped XHR errors. */
     var XHR_ERROR = 'XhrError';
     
     /**
      * Wraps an AJAX error as an Error object.
      */
     var wrap_ajax_error = function (jqXHR, status, error) {
         var wrapped_error = new Error(ajax_error_msg(jqXHR));
         wrapped_error.name =  XHR_ERROR;
         // provide xhr response
         wrapped_error.xhr = jqXHR;
         wrapped_error.xhr_status = status;
         wrapped_error.xhr_error = error;
         return wrapped_error;
     };
     
     var promising_ajax = function(url, settings) {
         // Like $.ajax, but returning an ES6 promise. success and error settings
         // will be ignored.
         return new Promise(function(resolve, reject) {
             settings.success = function(data, status, jqXHR) {
                 resolve(data);
             };
             settings.error = function(jqXHR, status, error) {
                 log_ajax_error(jqXHR, status, error);
                 reject(wrap_ajax_error(jqXHR, status, error));
             };
             $.ajax(url, settings);
         });
     };
 
-    var try_load = function(class_name, module_name, registry) {
+    var load = function(class_name, module_name, registry) {
         // Tries to load a class
         //
         // Tries to load a class from a module using require.js, if a module 
         // is specified, otherwise tries to load a class from the global 
         // registry, if the global registry is provided.
         return new Promise(function(resolve, reject) {
 
             // Try loading the view module using require.js
             if (module_name) {
                 require([module_name], function(module) {
                     if (module[class_name] === undefined) {
-                        reject(Error('Class not found in module.'));
+                        reject(new Error('Class not found in module.'));
                     } else {
                         resolve(module[class_name]);
                     }
                 }, reject);
             } else {
                 if (registry && registry[class_name]) {
                     resolve(registry[class_name]);
                 } else {
-                    reject(Error('Class not found in registry.'));
+                    reject(new Error('Class not found in registry.'));
                 }
             }
         });
     };
-    
+
     var utils = {
         regex_split : regex_split,
         uuid : uuid,
         fixConsole : fixConsole,
         fixCarriageReturn : fixCarriageReturn,
         autoLinkUrls : autoLinkUrls,
         points_to_pixels : points_to_pixels,
         get_body_data : get_body_data,
         parse_url : parse_url,
         url_path_split : url_path_split,
         url_path_join : url_path_join,
         url_join_encode : url_join_encode,
         encode_uri_components : encode_uri_components,
         splitext : splitext,
         escape_html : escape_html,
         always_new : always_new,
         to_absolute_cursor_pos : to_absolute_cursor_pos,
         from_absolute_cursor_pos : from_absolute_cursor_pos,
         browser : browser,
         platform: platform,
         is_or_has : is_or_has,
         is_focused : is_focused,
         mergeopt: mergeopt,
         ajax_error_msg : ajax_error_msg,
         log_ajax_error : log_ajax_error,
         requireCodeMirrorMode : requireCodeMirrorMode,
         XHR_ERROR : XHR_ERROR,
         wrap_ajax_error : wrap_ajax_error,
         promising_ajax : promising_ajax,
-        try_load: try_load,
+        load: load,
     };
 
     // Backwards compatability.
     IPython.utils = utils;
     
     return utils;
 }); 

IPython/html/static/widgets/js/manager.js

@@ -1,256 +1,231 b''
 // Copyright (c) IPython Development Team.
 // Distributed under the terms of the Modified BSD License.
 
 define([
     "underscore",
     "backbone",
     "jquery",
     "base/js/utils",
     "base/js/namespace"
 ], function (_, Backbone, $, utils, IPython) {
     "use strict";
     //--------------------------------------------------------------------
     // WidgetManager class
     //--------------------------------------------------------------------
     var WidgetManager = function (comm_manager, notebook) {
         // Public constructor
         WidgetManager._managers.push(this);
 
         // Attach a comm manager to the 
         this.keyboard_manager = notebook.keyboard_manager;
         this.notebook = notebook;
         this.comm_manager = comm_manager;
         this._models = {}; /* Dictionary of model ids and model instances */
 
         // Register with the comm manager.
         this.comm_manager.register_target('ipython.widget', $.proxy(this._handle_comm_open, this));
     };
 
     //--------------------------------------------------------------------
     // Class level
     //--------------------------------------------------------------------
     WidgetManager._model_types = {}; /* Dictionary of model type names (target_name) and model types. */
     WidgetManager._view_types = {}; /* Dictionary of view names and view types. */
     WidgetManager._managers = []; /* List of widget managers */
 
     WidgetManager.register_widget_model = function (model_name, model_type) {
         // Registers a widget model by name.
         WidgetManager._model_types[model_name] = model_type;
     };
 
     WidgetManager.register_widget_view = function (view_name, view_type) {
         // Registers a widget view by name.
         WidgetManager._view_types[view_name] = view_type;
     };
 
     //--------------------------------------------------------------------
     // Instance level
     //--------------------------------------------------------------------
     WidgetManager.prototype.display_view = function(msg, model) {
         // Displays a view for a particular model.
         var cell = this.get_msg_cell(msg.parent_header.msg_id);
         if (cell === null) {
             console.log("Could not determine where the display" + 
                 " message was from.  Widget will not be displayed");
         } else {
             var dummy = null;
             if (cell.widget_subarea) {
                 dummy = $('<div />');
                 cell.widget_subarea.append(dummy);
             }
 
             var that = this;
             this.create_view(model, {cell: cell}).then(function(view) {
                 that._handle_display_view(view);
                 if (dummy) {
                     dummy.replaceWith(view.$el);
                 }
                 view.trigger('displayed');
             }, $.proxy(console.error, console));
         }
     };
 
     WidgetManager.prototype._handle_display_view = function (view) {
         // Have the IPython keyboard manager disable its event
         // handling so the widget can capture keyboard input.
         // Note, this is only done on the outer most widgets.
         if (this.keyboard_manager) {
             this.keyboard_manager.register_events(view.$el);
         
             if (view.additional_elements) {
                 for (var i = 0; i < view.additional_elements.length; i++) {
                         this.keyboard_manager.register_events(view.additional_elements[i]);
                 }
             } 
         }
     };
     
 
     WidgetManager.prototype.create_view = function(model, options) {
-        // Creates a view for a particular model.
-        return new Promise(function(resolve, reject) {
-            var view_name = model.get('_view_name');
-            var view_module = model.get('_view_module');
-            utils.try_load(view_name, view_module, WidgetManager._view_types).then(function(ViewType){
-
-                // If a view is passed into the method, use that view's cell as
-                // the cell for the view that is created.
-                options = options || {};
-                if (options.parent !== undefined) {
-                    options.cell = options.parent.options.cell;
-                }
-
-                // Create and render the view...
-                var parameters = {model: model, options: options};
-                var view = new ViewType(parameters);
-                view.render();
-                model.on('destroy', view.remove, view);
-                resolve(view);
-            }, reject);
-        });
+        // Creates a promise for a view of a given model
+        return utils.load(model.get('_view_name'), model.get('_view_module'),
+                          WidgetManager._view_types).then(function(ViewType) {
+                              // If a view is passed into the method, use that view's cell as
+                              // the cell for the view that is created.
+                              options = options || {};
+                              if (options.parent !== undefined) {
+                                  options.cell = options.parent.options.cell;
+                              }
+                              // Create and render the view...
+                              var parameters = {model: model, options: options};
+                              var view = new ViewType(parameters);
+                              view.listenTo(model, 'destroy', view.remove);
+                              view.render();
+                              return view;
+                          });
     };
 
     WidgetManager.prototype.get_msg_cell = function (msg_id) {
         var cell = null;
         // First, check to see if the msg was triggered by cell execution.
         if (this.notebook) {
             cell = this.notebook.get_msg_cell(msg_id);
         }
         if (cell !== null) {
             return cell;
         }
         // Second, check to see if a get_cell callback was defined
         // for the message.  get_cell callbacks are registered for
         // widget messages, so this block is actually checking to see if the
         // message was triggered by a widget.
         var kernel = this.comm_manager.kernel;
         if (kernel) {
             var callbacks = kernel.get_callbacks_for_msg(msg_id);
             if (callbacks && callbacks.iopub &&
                 callbacks.iopub.get_cell !== undefined) {
                 return callbacks.iopub.get_cell();
             }
         }
         
         // Not triggered by a cell or widget (no get_cell callback 
         // exists).
         return null;
     };
 
     WidgetManager.prototype.callbacks = function (view) {
         // callback handlers specific a view
         var callbacks = {};
         if (view && view.options.cell) {
 
             // Try to get output handlers
             var cell = view.options.cell;
             var handle_output = null;
             var handle_clear_output = null;
             if (cell.output_area) {
                 handle_output = $.proxy(cell.output_area.handle_output, cell.output_area);
                 handle_clear_output = $.proxy(cell.output_area.handle_clear_output, cell.output_area);
             }
 
             // Create callback dictionary using what is known
             var that = this;
             callbacks = {
                 iopub : {
                     output : handle_output,
                     clear_output : handle_clear_output,
 
                     // Special function only registered by widget messages.
                     // Allows us to get the cell for a message so we know
                     // where to add widgets if the code requires it.
                     get_cell : function () {
                         return cell;
                     },
                 },
             };
         }
         return callbacks;
     };
 
     WidgetManager.prototype.get_model = function (model_id) {
-        // Look-up a model instance by its id.
-        var that = this;
-        var model = that._models[model_id];
-        if (model !== undefined) {
-            return new Promise(function(resolve, reject){
-                if (model instanceof Promise) {
-                    model.then(resolve, reject);
-                } else {
-                    resolve(model);
-                }
-            });
-        } else {
-            return undefined;
-        }
+        return that._models[model_id];
     };
 
     WidgetManager.prototype._handle_comm_open = function (comm, msg) {
         // Handle when a comm is opened.
         this.create_model({
             model_name: msg.content.data.model_name, 
             model_module: msg.content.data.model_module, 
             comm: comm});
     };
 
     WidgetManager.prototype.create_model = function (options) {
-        // Create and return a promise to create a new widget model.
+        // Create and return a promise for a new widget model
         //
         // Minimally, one must provide the model_name and widget_class
         // parameters to create a model from Javascript.
         //
         // Example
         // --------
         // JS:
         // IPython.notebook.kernel.widget_manager.create_model({
         //      model_name: 'WidgetModel', 
         //      widget_class: 'IPython.html.widgets.widget_int.IntSlider'})
         //      .then(function(model) { console.log('Create success!', model); },
         //      $.proxy(console.error, console));
         //
         // Parameters
         // ----------
         // options: dictionary
         //  Dictionary of options with the following contents:
         //      model_name: string
         //          Target name of the widget model to create.
         //      model_module: (optional) string
         //          Module name of the widget model to create.
         //      widget_class: (optional) string
         //          Target name of the widget in the back-end.
         //      comm: (optional) Comm
         
         // Create a comm if it wasn't provided.
         var comm = options.comm;
         if (!comm) {
             comm = this.comm_manager.new_comm('ipython.widget', {'widget_class': options.widget_class});
         }
 
         var that = this;
         var model_id = comm.comm_id;
-        var promise = new Promise(function(resolve, reject) {
-
-            // Get the model type using require or through the registry.
-            var widget_type_name = options.model_name;
-            var widget_module = options.model_module;
-            utils.try_load(widget_type_name, widget_module, WidgetManager._model_types)
-                .then(function(ModelType) {
-                    var widget_model = new ModelType(that, model_id, comm);
-                    widget_model.on('comm:close', function () {
-                      delete that._models[model_id];
-                    });
-                    that._models[model_id] = widget_model;
-                    resolve(widget_model);
-                }, reject);
-        });
-        this._models[model_id] = promise;
-        return promise;
+        var model_promise =  utils.load(options.model_name, options.model_module, WidgetManager._model_types)
+            .then(function(ModelType) {
+                var widget_model = new ModelType(that, model_id, comm);
+                widget_model.once('comm:close', function () {
+                    delete that._models[model_id];
+                });
+                return widget_model;
+            });
+        this._models[model_id] = model_promise;
+        return model_promise;
     };
 
     // Backwards compatibility.
     IPython.WidgetManager = WidgetManager;
 
     return {'WidgetManager': WidgetManager};
 });