Better error messages with correct stack traces

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

@@ -618,7 +618,8 b' define(['
             if (module_name) {
                 require([module_name], function(module) {
                     if (module[class_name] === undefined) {
-                        reject(new Error('Class not found in module.'));
+                        console.error('Class '+class_name+' not found in module '+module_name)
+                        reject();
                     } else {
                         resolve(module[class_name]);
                     }
@@ -627,7 +628,8 b' define(['
                 if (registry && registry[class_name]) {
                     resolve(registry[class_name]);
                 } else {
-                    reject(new Error('Class not found in registry.'));
+                    console.error('Class '+class_name+' not found in registry ', registry);
+                    reject();
                 }
             }
         });