Finished adding error handling.

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

@@ -97,7 +97,7 @@ define(["widgets/js/manager",
                 } finally {
                     that.state_lock = null;
                 }
-            }, $.proxy(console.error, console));
+            }, utils.reject("Couldn't set model state", true));
         },
 
         _handle_status: function (msg, callbacks) {
@@ -259,9 +259,9 @@ define(["widgets/js/manager",
                 });
                 return Promise.all(unpacked);
             } else if (value instanceof Object) {
-                var unpacked = {};
+                unpacked = {};
                 _.each(value, function(sub_value, key) {
-                    unpacked[key] = that._unpack_models(sub_value)
+                    unpacked[key] = that._unpack_models(sub_value);
                 });
                 return utils.resolve_dict(unpacked);
             } else if (typeof value === 'string' && value.slice(0,10) === "IPY_MODEL_") {

IPython/html/static/widgets/js/widget_box.js

@@ -78,13 +78,14 @@ define([
             var that = this;
             var dummy = $('<div/>');
             that.$box.append(dummy);
-            this.create_child_view(model).then(function(view) {
+            return this.create_child_view(model).then(function(view) {
                 dummy.replaceWith(view.el);
 
                 // Trigger the displayed event of the child view.
                 that.after_displayed(function() {
                     view.trigger('displayed');
                 });
+                return view;
             }, utils.reject("Couldn't add child view to box", true));
         },
     });

IPython/html/static/widgets/js/widget_selectioncontainer.js

@@ -116,7 +116,7 @@ define([
             
             var dummy = $('<div/>');
             accordion_inner.append(dummy);
-            this.create_child_view(model).then(function(view) {
+            return this.create_child_view(model).then(function(view) {
                 dummy.replaceWith(view.$el);
                 that.update();
                 that.update_titles();
@@ -125,7 +125,8 @@ define([
                 that.after_displayed(function() {
                     view.trigger('displayed');
                 });
-            }, $.proxy(console.error, console));
+                return view;
+            }, utils.reject("Couldn't add child view to box", true));
         },
     });
     
@@ -210,7 +211,7 @@ define([
                 .append(dummy)
                 .appendTo(that.$tab_contents);
 
-            this.create_child_view(model).then(function(view) {
+            return this.create_child_view(model).then(function(view) {
                 dummy.replaceWith(view.$el);
                 view.parent_tab = tab;
                 view.parent_container = contents_div;
@@ -219,7 +220,8 @@ define([
                 that.after_displayed(function() {
                     view.trigger('displayed');
                 });
-            }, $.proxy(console.error, console));
+                return view;
+            }, utils.reject("Couldn't add child view to box", true));
         },
 
         update: function(options) {