provides support for memoizing pathFn on effect;

only process effects/listeners if they exist.

src/lib/bind/accessors.html

@@ -14,10 +14,7 @@
     _dataEventCache: {},
 
     // for prototypes (usually)
-
     prepareModel: function(model) {
-      model._propertyEffects = {};
-      model._bindListeners = [];
       Polymer.Base.mixin(model, this._modelApi);
     },
 
@@ -106,6 +103,9 @@
     // a prepared model can acquire effects
 
     ensurePropertyEffects: function(model, property) {
+      if (!model._propertyEffects) {
+        model._propertyEffects = {};
+      }
       var fx = model._propertyEffects[property];
       if (!fx) {
         fx = model._propertyEffects[property] = [];
@@ -115,11 +115,13 @@
 
     addPropertyEffect: function(model, property, kind, effect) {
       var fx = this.ensurePropertyEffects(model, property);
-      fx.push({
+      var propEffect = {
         kind: kind,
         effect: effect,
         fn: Polymer.Bind['_' + kind + 'Effect']
-      });
+      };
+      fx.push(propEffect);
+      return propEffect;
     },
 
     createBindings: function(model) {
@@ -193,6 +195,9 @@
     },
 
     _addAnnotatedListener: function(model, index, property, path, event) {
+      if (!model._bindListeners) {
+        model._bindListeners = [];
+      }
       var fn = this._notedListenerFactory(property, path,
         this._isStructured(path));
       var eventName = event ||