Add a promise for app_initialized event.

See gh-2499

notebook/static/base/js/promises.js

@@ -0,0 +1,32 @@
+// Copyright (c) Jupyter Development Team.
+// Distributed under the terms of the Modified BSD License.
+
+// Give us an object to bind all events to. This object should be created
+// before all other objects so it exists when others register event handlers.
+// To register an event handler:
+//
+// require(['base/js/events'], function (events) {
+//     events.on("event.Namespace", function () { do_stuff(); });
+// });
+
+define(['base/js/events', 'base/js/namespace'], function(events, Jupyter) {
+    "use strict";
+
+    // Promise to be resolved when the application is initialized.
+    // The value is the name of the app on the current page.
+    var app_initialized = new Promise(function(resolve, reject) {
+        events.on('app_initialized.NotebookApp', function() {
+            resolve('NotebookApp');
+        });
+        events.on('app_initialized.DashboardApp', function() {
+            resolve('DashboardApp');
+        });
+    });
+
+    var promises = {
+        app_initialized: app_initialized
+    };
+    Jupyter.promises = promises;
+
+    return promises;
+});

notebook/static/notebook/js/main.js

@@ -29,6 +29,7 @@ require([
     'base/js/utils',
     'base/js/page',
     'base/js/events',
+    'base/js/promises',
     'auth/js/loginwidget',
     'notebook/js/maintoolbar',
     'notebook/js/pager',
@@ -52,6 +53,7 @@ require([
     utils,
     page,
     events,
+    promises,
     loginwidget,
     maintoolbar,
     pager,

notebook/static/tree/js/main.js

@@ -26,6 +26,7 @@ require([
     'base/js/namespace',
     'base/js/dialog',
     'base/js/events',
+    'base/js/promises',
     'base/js/page',
     'base/js/utils',
     'services/config',
@@ -41,6 +42,7 @@ require([
     IPython,
     dialog,
     events,
+    promises,
     page,
     utils,
     config,