feat(ngModel): expose $format function

Author: Narretz

src/ng/directive/ngModel.js

@@ -880,26 +880,34 @@ NgModelController.prototype = {
     this.$options = this.$options.createChild(options);
   },
 
-  $setModelValue: function(modelValue) {
-    this.$modelValue = this.$$rawModelValue = modelValue;
-    this.$$parserValid = undefined;
-
+  $format: function() {
     var formatters = this.$formatters,
         idx = formatters.length;
 
-    var viewValue = modelValue;
+    var viewValue = this.$modelValue;
     while (idx--) {
       viewValue = formatters[idx](viewValue);
     }
+
     if (this.$viewValue !== viewValue) {
       this.$$updateEmptyClasses(viewValue);
-      this.$viewValue = this.$$lastCommittedViewValue = viewValue;
-      this.$render();
+      this.$viewValue = this.$lastCommittedViewValue = viewValue;
+    }
 
+    return viewValue;
+  },
+
+  $setModelValue: function(modelValue) {
+    this.$modelValue = this.$$rawModelValue = modelValue;
+    this.$$parserValid = undefined;
+
+    if (this.$viewValue !== this.$format()) {
+      this.$render();
       // It is possible that model and view value have been updated during render
       this.$$runValidators(this.$modelValue, this.$viewValue, noop);
     }
   }
+
 };
 
 function setupModelWatcher(ctrl) {