feat(injector): support $inject(fn($service){}) function invocation

src/Injector.js

@@ -33,7 +33,9 @@
  *     `injector.eager()`
  */
 function createInjector(factories) {
-  var instanceCache = {$injector: injector};
+  var instanceCache = {
+    $injector: injector
+  };
   factories = factories || angularService;
 
   injector.invoke = invoke;
@@ -42,19 +44,23 @@ function createInjector(factories) {
     if (factory.$eager)
       injector(name);
   });
-  return injector;
+  return instanceCache.$injector;
 
   function injector(serviceId, path){
-    if (!(serviceId in instanceCache)) {
-      var factory = factories[serviceId];
-      path = path || [];
-      path.unshift(serviceId);
-      if (!factory) throw Error("Unknown provider for '" + path.join("' <- '") + "'.");
-      inferInjectionArgs(factory);
-      instanceCache[serviceId] = invoke(null, factory, [], path);
-      path.shift();
+    if (typeof serviceId == 'string') {
+      if (!(serviceId in instanceCache)) {
+        var factory = factories[serviceId];
+        path = path || [];
+        path.unshift(serviceId);
+        if (!factory) throw Error("Unknown provider for '" + path.join("' <- '") + "'.");
+        inferInjectionArgs(factory);
+        instanceCache[serviceId] = invoke(null, factory, [], path);
+        path.shift();
+      }
+      return instanceCache[serviceId];
+    } else {
+      return invoke(null, serviceId, path);
     }
-    return instanceCache[serviceId];
   }
 
   function invoke(self, fn, args, path){

test/InjectorSpec.js

@@ -83,6 +83,7 @@ describe('injector', function() {
 
     function fn(a, b, c, d) {
       args = [this, a, b, c, d];
+      return a + b + c + d;
     }
 
 
@@ -99,6 +100,11 @@ describe('injector', function() {
     });
 
 
+    it('should invoke the passed in function with all of the dependencies as arguments', function(){
+      expect(injector(['a', 'b', fn], [3, 4])).toEqual(10);
+    });
+
+
     it('should fail with errors if not function or array', function(){
       expect(function(){
         injector.invoke({}, {});