make ref bindable

R=arv
BUG=

Review URL: https://codereview.appspot.com/59220044

Author: rafaelw

src/TemplateBinding.js

@@ -326,6 +326,15 @@
     }
   }
 
+  var templateObserver;
+  if (typeof MutationObserver == 'function') {
+    templateObserver = new MutationObserver(function(records) {
+      for (var i = 0; i < records.length; i++) {
+        records[i].target.refChanged_();
+      }
+    });
+  }
+
   /**
    * Ensures proper API and content model for template elements.
    * @param {HTMLTemplateElement} opt_instanceRef The template element which
@@ -429,6 +438,25 @@
   }
 
   mixin(HTMLTemplateElement.prototype, {
+    bind: function(name, value, oneTime) {
+      if (name != 'ref')
+        return Element.prototype.bind.call(this, name, value, oneTime);
+
+      var self = this;
+      var ref = oneTime ? value : value.open(function(ref) {
+        self.setAttribute('ref', ref);
+        self.refChanged_();
+      });
+
+      this.setAttribute('ref', ref);
+      this.refChanged_();
+      if (oneTime)
+        return;
+
+      this.unbind('ref');
+      return this.bindings.ref = value;
+    },
+
     processBindingDirectives_: function(directives) {
       if (this.iterator_)
         this.iterator_.closeDeps();
@@ -450,6 +478,12 @@
       }
 
       this.iterator_.updateDependencies(directives, this.model_);
+
+      if (templateObserver) {
+        templateObserver.observe(this, { attributes: true,
+                                         attributeFilter: ['ref'] });
+      }
+
       return this.iterator_;
     },
 
@@ -458,7 +492,9 @@
       if (bindingDelegate)
         delegate_ = this.newDelegate_(bindingDelegate);
 
-      var content = this.ref_.content;
+      if (!this.refContent_)
+        this.refContent_ = this.ref_.content;
+      var content = this.refContent_;
       var map = this.bindingMap_;
       if (!map || map.content !== content) {
         // TODO(rafaelw): Setup a MutationObserver on content to detect
@@ -510,10 +546,20 @@
       return this.delegate_ && this.delegate_.raw;
     },
 
+    refChanged_: function() {
+      if (!this.iterator_ || this.refContent_ === this.ref_.content)
+        return;
+
+      this.refContent_ = undefined;
+      this.iterator_.valueChanged();
+      this.iterator_.updateIteratedValue();
+    },
+
     clear: function() {
       this.model_ = undefined;
       this.delegate_ = undefined;
       this.bindings_ = undefined;
+      this.refContent_ = undefined;
       if (!this.iterator_)
         return;
       this.iterator_.valueChanged();

tests/tests.js

@@ -1499,6 +1499,12 @@ suite('Template Instantiation', function() {
   });
 
   test('Update Ref', function(done) {
+    // Updating ref by observing the attribute is dependent on MutationObservers
+    if (typeof MutationObserver != 'function') {
+      done();
+      return;
+    }
+
     var div = createTestHtml(
         '<template id=A>Hi, {{}}</template>' +
         '<template id=B>Hola, {{}}</template>' +
@@ -1516,7 +1522,32 @@ suite('Template Instantiation', function() {
 
     }).then(function() {
       assert.strictEqual(5, div.childNodes.length);
+      assert.strictEqual('Hola, Fry', div.childNodes[3].textContent);
+      assert.strictEqual('Hola, Leela', div.childNodes[4].textContent);
+
+      done();
+    });
+  });
+
+  test('Bound Ref', function(done) {
+    var div = createTestHtml(
+        '<template id=A>Hi, {{}}</template>' +
+        '<template id=B>Hola, {{}}</template>' +
+        '<template ref="{{ ref }}" repeat="{{ people }}"></template>');
+    var template = div.childNodes[2];
+    var model = { ref: 'A', people: ['Fry'] };
+    template.model = model;
+
+    then(function() {
+      assert.strictEqual(4, div.childNodes.length);
       assert.strictEqual('Hi, Fry', div.childNodes[3].textContent);
+
+      model.ref = 'B';
+      model.people.push('Leela');
+
+    }).then(function() {
+      assert.strictEqual(5, div.childNodes.length);
+      assert.strictEqual('Hola, Fry', div.childNodes[3].textContent);
       assert.strictEqual('Hola, Leela', div.childNodes[4].textContent);
 
       done();