feat(input): hold listener during text composition

When composing text in CJKV, intermediate buffer for unfinished text should not
be updating the bound scope variables.

Closes angular#4684

src/ng/directive/input.js

@@ -392,8 +392,21 @@ var inputType = {
 
 
 function textInputType(scope, element, attr, ctrl, $sniffer, $browser) {
+  // In composition mode, users are still inputing intermediate text buffer,
+  // hold the listener until composition is done.
+  // More about composition events: https://developer.mozilla.org/en-US/docs/Web/API/CompositionEvent
+  var composing = false;
+
+  element.on('compositionstart', function() {
+    composing = true;
+  });
+
+  element.on('compositionend', function() {
+    composing = false;
+  });
 
   var listener = function() {
+    if (composing) return;
     var value = element.val();
 
     // By default we will trim the value

test/ng/directive/inputSpec.js

@@ -454,6 +454,20 @@ describe('input', function() {
     expect(scope.name).toEqual('adam');
   });
 
+  it('should not update the model between "compositionstart" and "compositionend"', function() {
+    compileInput('<input type="text" ng-model="name" name="alias"" />');
+    changeInputValueTo('a');
+    expect(scope.name).toEqual('a');
+    if (!(msie < 9)) {
+      browserTrigger(inputElm, 'compositionstart');
+      changeInputValueTo('adam');
+      expect(scope.name).toEqual('a');
+      browserTrigger(inputElm, 'compositionend');
+    }
+    changeInputValueTo('adam');
+    expect(scope.name).toEqual('adam');
+  });
+
   describe('"paste" and "cut" events', function() {
     beforeEach(function() {
       // Force browser to report a lack of an 'input' event