feat($injector): support instantiating classes.

ES6's `class Foo {}` constructors cannot be instantiated using
`fn.apply`. This change extracts injection argument collection and then
uses new (Function.bind.apply(ctor, args)) to instantiate the service
instance.

Author: mprobst

src/auto/injector.js

@@ -795,48 +795,54 @@ function createInjector(modulesToLoad, strictDi) {
       }
     }
 
-    function invoke(fn, self, locals, serviceName) {
-      if (typeof locals === 'string') {
-        serviceName = locals;
-        locals = null;
-      }
 
+    function injectionArgs(fn, locals, serviceName) {
       var args = [],
-          $inject = createInjector.$$annotate(fn, strictDi, serviceName),
-          length, i,
-          key;
+          $inject = createInjector.$$annotate(fn, strictDi, serviceName);
 
-      for (i = 0, length = $inject.length; i < length; i++) {
-        key = $inject[i];
+      for (var i = 0, length = $inject.length; i < length; i++) {
+        var key = $inject[i];
         if (typeof key !== 'string') {
           throw $injectorMinErr('itkn',
                   'Incorrect injection token! Expected service name as string, got {0}', key);
         }
-        args.push(
-          locals && locals.hasOwnProperty(key)
-          ? locals[key]
-          : getService(key, serviceName)
-        );
+        args.push(locals && locals.hasOwnProperty(key) ? locals[key] :
+                                                         getService(key, serviceName));
       }
+      return args;
+    }
+
+
+    function invoke(fn, self, locals, serviceName) {
+      if (typeof locals === 'string') {
+        serviceName = locals;
+        locals = null;
+      }
+
+      var args = injectionArgs(fn, locals, serviceName);
       if (isArray(fn)) {
-        fn = fn[length];
+        fn = fn[fn.length - 1];
       }
 
       // http://jsperf.com/angularjs-invoke-apply-vs-switch
       // #5388
       return fn.apply(self, args);
     }
 
+
     function instantiate(Type, locals, serviceName) {
       // Check if Type is annotated and use just the given function at n-1 as parameter
       // e.g. someModule.factory('greeter', ['$window', function(renamed$window) {}]);
-      // Object creation: http://jsperf.com/create-constructor/2
-      var instance = Object.create((isArray(Type) ? Type[Type.length - 1] : Type).prototype || null);
-      var returnedValue = invoke(Type, instance, locals, serviceName);
-
-      return isObject(returnedValue) || isFunction(returnedValue) ? returnedValue : instance;
+      var ctor = (isArray(Type) ? Type[Type.length - 1] : Type);
+      var args = injectionArgs(Type, locals, serviceName);
+      // Empty object at position 0 is ignored for invocation with `new`, but required.
+      args.unshift({});
+      /*jshint -W058 */ // Applying a constructor without immediate parentheses is the point here.
+      return new (Function.prototype.bind.apply(ctor, args));
+      /*jshint +W058 */
     }
 
+
     return {
       invoke: invoke,
       instantiate: instantiate,

test/auto/injectorSpec.js

@@ -245,12 +245,24 @@ describe('injector', function() {
 
     // Only Chrome and Firefox support this syntax.
     if (/chrome|firefox/i.test(navigator.userAgent)) {
-      it('should be possible to annotate functions that are declared using ES6 syntax', function() {
-        /*jshint -W061 */
-        // The function is generated using `eval` as just having the ES6 syntax can break some browsers.
-        expect(annotate(eval('({ fn(x) { return; } })').fn)).toEqual(['x']);
-        /*jshint +W061 */
+      /*jshint -W061 */
+      describe('ES6 syntax', function() {
+        // Functions and classes are generated using `eval` as just having the ES6 syntax can break
+        // some browsers.
+        it('should be possible to annotate ES6 methods',
+           function() { expect(annotate(eval('({ fn(x) { return; } })').fn)).toEqual(['x']); });
+
+        it('should be possible to instantiate ES6 classes', function() {
+          // Only Chrome (not even the FF we use) supports ES6 classes.
+          if (!/chrome/i.test(navigator.userAgent)) return;
+          providers('a', function() { return 'a-value'; });
+          var clazz = eval('(class { constructor(a) { this.a = a; } aVal() { return this.a; } })');
+          var instance = injector.instantiate(clazz);
+          expect(instance).toEqual({a: 'a-value'});
+          expect(instance.aVal()).toEqual('a-value');
+        });
       });
+      /*jshint +W061 */
     }