Debounce $scope updates when typing in chat. (#8485)

Fixes #6462, by saving a bunch of time per frame. See the issue for evidence of
the win.

test/client-old/spec/controllers/chatCtrlSpec.js

@@ -1,14 +1,14 @@
 'use strict';
 
 describe("Chat Controller", function() {
-  var scope, ctrl, user, $rootScope, $controller;
+  var scope, ctrl, user, $rootScope, $controller, $httpBackend, html;
 
   beforeEach(function() {
     module(function($provide) {
       $provide.value('User', {});
     });
 
-    inject(function(_$rootScope_, _$controller_){
+    inject(function(_$rootScope_, _$controller_, _$compile_, _$httpBackend_){
       user = specHelper.newUser();
       user._id = "unique-user-id";
       $rootScope = _$rootScope_;
@@ -16,13 +16,20 @@ describe("Chat Controller", function() {
       scope = _$rootScope_.$new();
 
       $controller = _$controller_;
+      $httpBackend = _$httpBackend_;
 
       // Load RootCtrl to ensure shared behaviors are loaded
       $controller('RootCtrl',  {$scope: scope, User: {user: user}});
 
-      ctrl = $controller('ChatCtrl', {$scope: scope});
+      html = _$compile_('<div><form ng-submit="postChat(group, message.content)"><textarea submit-on-meta-enter ng-model="message.content" ng-model-options="{debounce: 250}"></textarea></form></div>')(scope);
+      document.body.appendChild(html[0]);
+      ctrl = $controller('ChatCtrl', {$scope: scope, $element: html});
     });
   });
+  
+  afterEach(function() {
+    html.remove();
+  });
 
   describe('copyToDo', function() {
     it('when copying a user message it opens modal with information from message', function() {
@@ -68,5 +75,47 @@ describe("Chat Controller", function() {
       }));
     });
   });
+  
+  it('updates model on enter key press', function() {
+    // Set initial state of the page with some dummy data.
+    scope.group = { name: 'group' };
+    
+    // The main controller is going to try to fetch the template right off. 
+    // No big deal, just return an empty string.
+    $httpBackend.when('GET', 'partials/main.html').respond('');
+
+    // Let the page settle, and the controllers set their initial state.
+    $rootScope.$digest();
+
+    // Watch for calls to postChat & make sure it doesn't do anything.
+    let postChatSpy = sandbox.stub(scope, 'postChat');
+    
+    // Pretend we typed 'aaa' into the textarea.
+    var textarea = html.find('textarea');    
+    textarea[0].value = 'aaa';
+    let inputEvent = new Event('input');
+    textarea[0].dispatchEvent(inputEvent);
+
+    // Give a change for the ng-model watchers to notice that the value in the
+    // textarea has changed.
+    $rootScope.$digest();
+    
+    // Since no time has elapsed and we debounce the model change, we should 
+    // see no model update just yet.
+    expect(scope.message.content).to.equal('');
+    
+    // Now, press the enter key in the textarea. We use jquery here to paper 
+    // over browser differences with initializing the keyboard event.
+    var keyboardEvent = jQuery.Event('keydown', {keyCode: 13, key: 'Enter', metaKey: true});
+    jQuery(textarea).trigger(keyboardEvent);
+
+    // Now, allow the model to update given the changes to the page still
+    // without letting any time elapse...
+    $rootScope.$digest();
+    
+    // ... and nevertheless seeing the desired call to postChat with the right
+    // data. Yay!
+    postChatSpy.should.have.been.calledWith(scope.group, 'aaa');
+  });
 });