fix($watchGroup): call listener once when the watchExpressions array is empty

Author: rodyhaddad

src/ng/rootScope.js

@@ -392,6 +392,17 @@ function $RootScopeProvider(){
         var changeReactionScheduled = false;
         var firstRun = true;
 
+        if (!watchExpressions.length) {
+          // No expressions means we call the listener ASAP
+          var shouldCall = true;
+          self.$evalAsync(function () {
+            if (shouldCall) listener(newValues, newValues, self);
+          });
+          return function deregisterWatchGroup() {
+            shouldCall = false;
+          }
+        }
+
         if (watchExpressions.length === 1) {
           // Special case size of one
           return this.$watch(watchExpressions[0], function watchGroupAction(value, oldValue, scope) {

test/ng/rootScopeSpec.js

@@ -844,59 +844,80 @@ describe('Scope', function() {
     }));
 
 
-    it('should work for a group with just a single expression', function() {
-      scope.$watchGroup(['a'], function(values, oldValues, s) {
+    it('should detect a change to any one expression in the group', function() {
+      scope.$watchGroup(['a', 'b'], function(values, oldValues, s) {
         expect(s).toBe(scope);
         log(oldValues + ' >>> ' + values);
       });
 
       scope.a = 'foo';
+      scope.b = 'bar';
       scope.$digest();
-      expect(log).toEqual('foo >>> foo');
+      expect(log).toEqual('foo,bar >>> foo,bar');
 
       log.reset();
       scope.$digest();
       expect(log).toEqual('');
 
-      scope.a = 'bar';
+      scope.a = 'a';
       scope.$digest();
-      expect(log).toEqual('foo >>> bar');
+      expect(log).toEqual('foo,bar >>> a,bar');
+
+      log.reset();
+      scope.a = 'A';
+      scope.b = 'B';
+      scope.$digest();
+      expect(log).toEqual('a,bar >>> A,B');
     });
 
 
-    it('should detect a change to any one expression in the group', function() {
-      scope.$watchGroup(['a', 'b'], function(values, oldValues, s) {
+    it('should work for a group with just a single expression', function() {
+      scope.$watchGroup(['a'], function(values, oldValues, s) {
         expect(s).toBe(scope);
         log(oldValues + ' >>> ' + values);
       });
 
       scope.a = 'foo';
-      scope.b = 'bar';
       scope.$digest();
-      expect(log).toEqual('foo,bar >>> foo,bar');
+      expect(log).toEqual('foo >>> foo');
 
       log.reset();
       scope.$digest();
       expect(log).toEqual('');
 
-      scope.a = 'a';
+      scope.a = 'bar';
       scope.$digest();
-      expect(log).toEqual('foo,bar >>> a,bar');
+      expect(log).toEqual('foo >>> bar');
+    });
+
+
+    it('should call the listener once when the array of watchExpressions is empty', function() {
+      scope.$watchGroup([], function(values, oldValues) {
+        log(oldValues + ' >>> ' + values);
+      });
+
+      expect(log).toEqual('');
+      scope.$digest();
+      expect(log).toEqual(' >>> ');
 
       log.reset();
-      scope.a = 'A';
-      scope.b = 'B';
       scope.$digest();
-      expect(log).toEqual('a,bar >>> A,B');
+      expect(log).toEqual('');
     });
 
 
     it('should not call watch action fn when watchGroup was deregistered', function() {
-      var deregister = scope.$watchGroup(['a', 'b'], function(values, oldValues) {
+      var deregisterMany = scope.$watchGroup(['a', 'b'], function(values, oldValues) {
+        log(oldValues + ' >>> ' + values);
+      }), deregisterOne = scope.$watchGroup(['a'], function(values, oldValues) {
+        log(oldValues + ' >>> ' + values);
+      }), deregisterNone = scope.$watchGroup([], function(values, oldValues) {
         log(oldValues + ' >>> ' + values);
       });
 
-      deregister();
+      deregisterMany();
+      deregisterOne();
+      deregisterNone();
       scope.a = 'xxx';
       scope.b = 'yyy';
       scope.$digest();