perf($rootScope): only creating $$listeners and $$listenerCount when required

- this avoids creating 2 JSON objects per scope until: registering a listener ($$listeners) or a child registering a listener ($$listenerCount)

Author: jbedard

src/ng/rootScope.js

@@ -132,8 +132,7 @@ function $RootScopeProvider(){
       this.$$destroyed = false;
       this.$$asyncQueue = [];
       this.$$postDigestQueue = [];
-      this.$$listeners = {};
-      this.$$listenerCount = {};
+      this.$$listeners = this.$$listenerCount = null;
       this.$$isolateBindings = null;
       this.$$applyAsyncQueue = [];
     }
@@ -203,8 +202,7 @@ function $RootScopeProvider(){
             this.$$ChildScope = function ChildScope() {
               this.$$watchers = this.$$nextSibling =
                   this.$$childHead = this.$$childTail = null;
-              this.$$listeners = {};
-              this.$$listenerCount = {};
+              this.$$listeners = this.$$listenerCount = null;
               this.$id = nextUid();
               this.$$ChildScope = null;
             };
@@ -871,11 +869,10 @@ function $RootScopeProvider(){
         // - https://github.com/angular/angular.js/issues/1313#issuecomment-10378451
 
         this.$parent = this.$$nextSibling = this.$$prevSibling = this.$$childHead =
-            this.$$childTail = this.$root = null;
+            this.$$childTail = this.$root = this.$$watchers = this.$$listeners = null;
 
         // don't reset these to null in case some async task tries to register a listener/watch/task
-        this.$$listeners = {};
-        this.$$watchers = this.$$asyncQueue = this.$$postDigestQueue = [];
+        this.$$asyncQueue = this.$$postDigestQueue = [];
 
         // prevent NPEs since these methods have references to properties we nulled out
         this.$destroy = this.$digest = this.$apply = noop;
@@ -1078,14 +1075,17 @@ function $RootScopeProvider(){
        * @returns {function()} Returns a deregistration function for this listener.
        */
       $on: function(name, listener) {
-        var namedListeners = this.$$listeners[name];
+        var namedListeners = (this.$$listeners || (this.$$listeners = {}))[name];
         if (!namedListeners) {
           this.$$listeners[name] = namedListeners = [];
         }
         namedListeners.push(listener);
 
         var current = this;
         do {
+          if (!current.$$listenerCount) {
+            current.$$listenerCount = {};
+          }
           if (!current.$$listenerCount[name]) {
             current.$$listenerCount[name] = 0;
           }
@@ -1140,7 +1140,7 @@ function $RootScopeProvider(){
             i, length;
 
         do {
-          namedListeners = scope.$$listeners[name] || empty;
+          namedListeners = scope.$$listeners && scope.$$listeners[name] || empty;
           event.currentScope = scope;
           for (i=0, length=namedListeners.length; i<length; i++) {
 
@@ -1207,15 +1207,15 @@ function $RootScopeProvider(){
               defaultPrevented: false
             };
 
-        if (!target.$$listenerCount[name]) return event;
+        if (!(target.$$listenerCount && target.$$listenerCount[name])) return event;
 
         var listenerArgs = concat([event], arguments, 1),
             listeners, i, length;
 
         //down while you can, then up and next sibling or up and next sibling until back at root
         while ((current = next)) {
           event.currentScope = current;
-          listeners = current.$$listeners[name] || [];
+          listeners = current.$$listeners && current.$$listeners[name] || [];
           for (i=0, length = listeners.length; i<length; i++) {
             // if listeners were deregistered, defragment the array
             if (!listeners[i]) {
@@ -1236,7 +1236,7 @@ function $RootScopeProvider(){
           // yes, this code is a bit crazy, but it works and we have tests to prove it!
           // this piece should be kept in sync with the traversal in $digest
           // (though it differs due to having the extra check for $$listenerCount)
-          if (!(next = ((current.$$listenerCount[name] && current.$$childHead) ||
+          if (!(next = ((current.$$listenerCount && current.$$listenerCount[name] && current.$$childHead) ||
               (current !== target && current.$$nextSibling)))) {
             while(current !== target && !(next = current.$$nextSibling)) {
               current = current.$parent;