Add promise for notebook_loaded.Notebook event

Author: takluyver

notebook/static/base/js/promises.js

@@ -1,13 +1,7 @@
 // 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 an object to attach promises to for one-time events.
 
 define(['base/js/events', 'base/js/namespace'], function(events, Jupyter) {
     "use strict";

notebook/static/notebook/js/main.js

@@ -33,6 +33,7 @@ require([
     'auth/js/loginwidget',
     'notebook/js/maintoolbar',
     'notebook/js/pager',
+    'notebook/js/promises',
     'notebook/js/quickhelp',
     'notebook/js/menubar',
     'notebook/js/notificationarea',
@@ -57,6 +58,7 @@ require([
     loginwidget,
     maintoolbar,
     pager,
+    nb_promises,
     quickhelp,
     menubar,
     notificationarea,

notebook/static/notebook/js/promises.js

@@ -0,0 +1,22 @@
+// Copyright (c) Jupyter Development Team.
+// Distributed under the terms of the Modified BSD License.
+
+// Define promises for notebook events.
+
+define(['base/js/events', 'base/js/promises'], function(events, promises) {
+    "use strict";
+
+    // Promise to be resolved when the notebook is *initially* loaded.
+    // The event may fire again if the notebook is reloaded later, but this
+    // promise only tracks the initial load.
+    promises.notebook_loaded = new Promise(function(resolve, reject) {
+        events.one('notebook_loaded.Notebook', function() {
+            resolve();
+        });
+        events.one('notebook_load_failed.Notebook', function() {
+            reject();
+        });
+    });
+
+    return promises;
+});