Register widget models and views that have the right inheritance, rather than the right name.

Thanks to @jdfreder for this suggestion.

IPython/html/static/widgets/js/init.js

@@ -3,6 +3,7 b''
 
 define([
     "widgets/js/manager",
+    "widgets/js/widget",
     "widgets/js/widget_link",
     "widgets/js/widget_bool",
     "widgets/js/widget_button",
@@ -14,36 +15,20 b' define(['
     "widgets/js/widget_selection",
     "widgets/js/widget_selectioncontainer",
     "widgets/js/widget_string",
-], function(widgetmanager) {
-
-
-    /**
-     * From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/endsWith
-     * Can be removed with the string endsWith function is implemented in major browsers
-     */
-    var endsWith = function(target, searchString, position) {
-        var subjectString = target.toString();
-        if (position === undefined || position > subjectString.length) {
-            position = subjectString.length;
-        }
-        position -= searchString.length;
-        var lastIndex = subjectString.indexOf(searchString, position);
-        return lastIndex !== -1 && lastIndex === position;
-    };
-
+], function(widgetmanager, widget) {
     // Register all of the loaded models and views with the widget manager.
-    for (var i = 1; i < arguments.length; i++) {
+    for (var i = 2; i < arguments.length; i++) {
         var module = arguments[i];
         for (var target_name in module) {
             if (module.hasOwnProperty(target_name)) {
-                if (endsWith(target_name, "View")) {
-                    widgetmanager.WidgetManager.register_widget_view(target_name, module[target_name]);
-                } else if (endsWith(target_name, "Model")) {
-                    widgetmanager.WidgetManager.register_widget_model(target_name, module[target_name]);
+                var target = module[target_name];
+                if (target.prototype instanceof widget.WidgetModel) {
+                    widgetmanager.WidgetManager.register_widget_model(target_name, target);
+                } else if (target.prototype instanceof widget.WidgetView) {
+                    widgetmanager.WidgetManager.register_widget_view(target_name, target);
                 }
             }
         }
     }
-
     return {'WidgetManager': widgetmanager.WidgetManager}; 
 });