feat(Binding): improve errors

fix #4358

Closes #4360

modules/angular2/src/core/di/binding.ts

@@ -6,6 +6,8 @@ import {
   CONST_EXPR,
   stringify,
   isArray,
+  isType,
+  isFunction,
   normalizeBool
 } from 'angular2/src/core/facade/lang';
 import {BaseException, WrappedException} from 'angular2/src/core/facade/exceptions';
@@ -344,7 +346,13 @@ export class BindingBuilder {
    * expect(injectorAlias.get(Vehicle) instanceof Car).toBe(true);
    * ```
    */
-  toClass(type: Type): Binding { return new Binding(this.token, {toClass: type}); }
+  toClass(type: Type): Binding {
+    if (!isType(type)) {
+      throw new BaseException(
+          `Trying to create a class binding but "${stringify(type)}" is not a class!`);
+    }
+    return new Binding(this.token, {toClass: type});
+  }
 
   /**
    * Binds a DI token to a value.
@@ -416,8 +424,12 @@ export class BindingBuilder {
    * expect(injector.get(String)).toEqual('Value: 3');
    * ```
    */
-  toFactory(factoryFunction: Function, dependencies?: any[]): Binding {
-    return new Binding(this.token, {toFactory: factoryFunction, deps: dependencies});
+  toFactory(factory: Function, dependencies?: any[]): Binding {
+    if (!isFunction(factory)) {
+      throw new BaseException(
+          `Trying to create a factory binding but "${stringify(factory)}" is not a function!`);
+    }
+    return new Binding(this.token, {toFactory: factory, deps: dependencies});
   }
 }
 

modules/angular2/test/core/di/binding_spec.ts

@@ -0,0 +1,31 @@
+import {
+  AsyncTestCompleter,
+  beforeEach,
+  ddescribe,
+  describe,
+  expect,
+  iit,
+  inject,
+  it,
+  xit,
+} from 'angular2/test_lib';
+
+import {bind} from 'angular2/core';
+
+export function main() {
+  describe('binding', () => {
+
+    describe('type errors', () => {
+
+      it('should throw when trying to create a class binding and not passing a class', () => {
+        expect(() => { bind('foo').toClass(<any>0); })
+            .toThrowError('Trying to create a class binding but "0" is not a class!');
+      });
+
+      it('should throw when trying to create a factory binding and not passing a function', () => {
+        expect(() => { bind('foo').toFactory(<any>0); })
+            .toThrowError('Trying to create a factory binding but "0" is not a function!');
+      });
+    });
+  });
+}