feat(web components): Support custom events for element property binding

Closes #1449
Closes #1453

Author: jbdeboer

lib/core/annotation_src.dart

@@ -203,14 +203,28 @@ abstract class Directive {
    */
   final List<String> exportExpressions;
 
+  /**
+   * Event names to listen to during Web Component two-way binding.
+   *
+   * To support web components efficiently, Angular only reads element
+   * bindings when specific events are fired.  By default, Angular listens
+   * to 'change'.  Adding events names to this listen will cause Angular
+   * to listen to those events instead.
+   *
+   * The name is intentionally long: this should be rarely used and therefore
+   * it is important that it is self-documenting.
+   */
+  final List<String> updateBoundElementPropertiesOnEvents;
+
   const Directive({
     this.selector,
     this.children,
     this.visibility,
     this.module,
     this.map: const {},
     this.exportExpressions: const [],
-    this.exportExpressionAttrs: const []
+    this.exportExpressionAttrs: const [],
+    this.updateBoundElementPropertiesOnEvents
   });
 
   toString() => selector;
@@ -282,15 +296,17 @@ class Component extends Directive {
     exportExpressions,
     exportExpressionAttrs,
     this.useShadowDom,
-    this.useNgBaseCss: true})
-      : _cssUrls = cssUrl,
+    this.useNgBaseCss: true,
+    updateBoundElementPropertiesOnEvents
+  }) : _cssUrls = cssUrl,
         super(selector: selector,
              children: Directive.COMPILE_CHILDREN,
              visibility: visibility,
              map: map,
              module: module,
              exportExpressions: exportExpressions,
-             exportExpressionAttrs: exportExpressionAttrs);
+             exportExpressionAttrs: exportExpressionAttrs,
+             updateBoundElementPropertiesOnEvents: updateBoundElementPropertiesOnEvents);
 
   List<String> get cssUrls => _cssUrls == null ?
       const [] :
@@ -309,7 +325,8 @@ class Component extends Directive {
           exportExpressions: exportExpressions,
           exportExpressionAttrs: exportExpressionAttrs,
           useShadowDom: useShadowDom,
-          useNgBaseCss: useNgBaseCss);
+          useNgBaseCss: useNgBaseCss,
+          updateBoundElementPropertiesOnEvents: updateBoundElementPropertiesOnEvents);
 }
 
 /**
@@ -332,14 +349,16 @@ class Decorator extends Directive {
                     DirectiveBinderFn module,
                     visibility,
                     exportExpressions,
-                    exportExpressionAttrs})
+                    exportExpressionAttrs,
+                    updateBoundElementPropertiesOnEvents})
       : super(selector: selector,
               children: children,
               visibility: visibility,
               map: map,
               module: module,
               exportExpressions: exportExpressions,
-              exportExpressionAttrs: exportExpressionAttrs);
+              exportExpressionAttrs: exportExpressionAttrs,
+              updateBoundElementPropertiesOnEvents: updateBoundElementPropertiesOnEvents);
 
   Directive _cloneWithNewMap(newMap) =>
       new Decorator(
@@ -349,7 +368,8 @@ class Decorator extends Directive {
           selector: selector,
           visibility: visibility,
           exportExpressions: exportExpressions,
-          exportExpressionAttrs: exportExpressionAttrs);
+          exportExpressionAttrs: exportExpressionAttrs,
+          updateBoundElementPropertiesOnEvents: updateBoundElementPropertiesOnEvents);
 }
 
 /**

lib/core_dom/element_binder.dart

@@ -59,6 +59,20 @@ class ElementBinder {
   bool get shouldCompileChildren =>
       childMode == Directive.COMPILE_CHILDREN;
 
+  List<String> _bindAssignablePropsOnCache;
+  List<String> get _bindAssignablePropsOn {
+    if (_bindAssignablePropsOnCache != null) return _bindAssignablePropsOnCache;
+    _bindAssignablePropsOnCache = [];
+    _usableDirectiveRefs.forEach((DirectiveRef ref) {
+      var eventNames = ref.annotation.updateBoundElementPropertiesOnEvents;
+      if (eventNames != null) {
+        _bindAssignablePropsOnCache.addAll(eventNames);
+      }
+    });
+    if (_bindAssignablePropsOnCache.isEmpty) _bindAssignablePropsOnCache.add('change');
+    return _bindAssignablePropsOnCache;
+  }
+
   var _directiveCache;
   List<DirectiveRef> get _usableDirectiveRefs {
     if (_directiveCache != null) return _directiveCache;
@@ -308,13 +322,11 @@ class ElementBinder {
       // due to https://code.google.com/p/dart/issues/detail?id=17406
       // we have to manually run the zone.
       var zone = Zone.current;
-      node.addEventListener('change', (_) =>
-        zone.run(() =>
-          bindAssignableProps.forEach((propAndExp) =>
-            propAndExp[1].assign(scope.context, jsNode[propAndExp[0]])
-          )
-        )
-      );
+      _bindAssignablePropsOn.forEach((String eventName) =>
+	      node.addEventListener(eventName, (_) =>
+	        zone.run(() =>
+	          bindAssignableProps.forEach((propAndExp) =>
+	            propAndExp[1].assign(scope.context, jsNode[propAndExp[0]])))));
     }
 
     if (onEvents.isNotEmpty) {

test/core/annotation_src_spec.dart

@@ -44,7 +44,8 @@ void main() => describe('annotations', () {
         visibility: Directive.LOCAL_VISIBILITY,
         exportExpressions: [],
         exportExpressionAttrs: [],
-        useShadowDom: true
+        useShadowDom: true,
+        updateBoundElementPropertiesOnEvents: []
       );
 
       // Check that no fields are null
@@ -64,7 +65,8 @@ void main() => describe('annotations', () {
           module: (i){},
           visibility: Directive.LOCAL_VISIBILITY,
           exportExpressions: [],
-          exportExpressionAttrs: []
+          exportExpressionAttrs: [],
+          updateBoundElementPropertiesOnEvents: []
       );
 
       // Check that no fields are null

test/core_dom/web_components_spec.dart

@@ -43,6 +43,10 @@ main() {
     beforeEach((TestBed tb) {
       _ = tb;
     });
+
+    beforeEachModule((Module m) {
+      m.bind(TestsTwoWayCustom);
+    });
 
     it('should create custom elements', () {
       registerElement('tests-basic', {'prop-x': 6});
@@ -89,5 +93,26 @@ main() {
 
       expect(_.rootScope.context['x']).toEqual(6);
     });
+
+    it('should support two-way bindings for components that trigger a defined event', () {
+      registerElement('tests-twoway-custom', {});
+      compileAndUpgrade('<tests-twoway-custom bind-prop="x"></tests-twoway-custom>');
+
+      setCustomProp('prop', 6);
+      _.rootElement.dispatchEvent(new Event.eventType('CustomEvent', 'x-change'));
+
+      expect(_.rootScope.context['x']).toEqual(6);
+
+      // The change event should not cause an update
+      setCustomProp('prop', 7);
+      _.rootElement.dispatchEvent(new Event.eventType('CustomEvent', 'change'));
+      expect(_.rootScope.context['x']).toEqual(6);
+    });
   });
 }
+
+@Decorator(
+  selector: 'tests-twoway-custom',
+  updateBoundElementPropertiesOnEvents: const ['x-change']
+)
+class TestsTwoWayCustom {}