getInstanceModel -> prepareInstanceModel

R=arv
BUG=

Review URL: https://codereview.appspot.com/13577043

Author: rafaelw

src/TemplateBinding.js

@@ -1012,11 +1012,13 @@
         return;
       }
 
-      var delegate = template.bindingDelegate;
-      var delegateInstanceModelFn =
-          delegate && typeof delegate.getInstanceModel === 'function' ?
-          delegate.getInstanceModel : undefined;
-
+      if (this.instanceModelFn_ === undefined) {
+        var delegate = template.bindingDelegate;
+        if (delegate && typeof delegate.prepareInstanceModel === 'function')
+          this.instanceModelFn_ = delegate.prepareInstanceModel(template);
+        if (typeof this.instanceModelFn_ !== 'function')
+          this.instanceModelFn_ = false;
+      }
 
       var instanceCache = new Map;
       var removeDelta = 0;
@@ -1042,8 +1044,8 @@
             bound = instanceNodes.bound;
           } else {
             bound = [];
-            if (delegateInstanceModelFn)
-              model = delegateInstanceModelFn(template, model);
+            if (this.instanceModelFn_)
+              model = this.instanceModelFn_(model);
 
             if (model !== undefined) {
               fragment = this.templateElement_.createInstance(model,

tests/tests.js

@@ -1918,28 +1918,31 @@ suite('Binding Delegate API', function() {
     var testData = [
       {
         template: template,
+      },
+      {
         model: model[0],
         altModel: { foo: 'a' }
       },
       {
-        template: template,
         model: model[1],
         altModel: { foo: 'b' }
       },
       {
-        template: template,
         model: model[2],
         altModel: { foo: 'c' }
       }
     ];
 
     var delegate = {
-      getInstanceModel: function(template, model) {
+      prepareInstanceModel: function(template) {
         var data = testData.shift();
-
         assert.strictEqual(data.template, template);
-        assert.strictEqual(data.model, model);
-        return data.altModel;
+
+        return function(model) {
+          data = testData.shift();
+          assert.strictEqual(data.model, model);
+          return data.altModel;
+        }
       }
     };
 
@@ -1961,22 +1964,28 @@ suite('Binding Delegate API', function() {
         '<template repeat>' +
         '{{}}</template>');
     var template = div.firstChild;
-    var count = 0;
+    var prepareCount = 0;
+    var callCount = 0;
 
     var delegate = {
-      getInstanceModel: function(template, model) {
-        count++;
-        return model;
+      prepareInstanceModel: function(template) {
+        prepareCount++;
+        return function(model) {
+          callCount++;
+          return model;
+        };
       }
     };
 
     recursivelySetTemplateModel(div, model, delegate);
     Platform.performMicrotaskCheckpoint();
-    assert.strictEqual(3, count);
+    assert.strictEqual(1, prepareCount);
+    assert.strictEqual(3, callCount);
 
     model.reverse();
     Platform.performMicrotaskCheckpoint();
-    assert.strictEqual(3, count);
+    assert.strictEqual(1, prepareCount);
+    assert.strictEqual(3, callCount);
   });
 
   test('Basic', function() {