feat: support import() spec

Support the [Dynamic import proposal](https://github.com/tc39/proposal-dynamic-import) [TC39 Stage 3] as a loader (codegen).
The import() construct is supported in webpack from 2.1.0-beta28

Also adds decprecation message then using async-system (System.import) as it will be removed from webpack 3+

BREAKING CHANGES:
Typescript transform `import(...)` syntax into something.
To use `ng-router-loader` with `async-import` code generator the `ng-router-loader` must
 run **AFTER** the TS compiler (e.g: awesome-typescript-loader), that is in a lower index in the loaders array.
 This also requires the code generators to emit ES5 code.
SEE: microsoft/TypeScript#12364

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ng-router-loader",
-  "version": "1.0.2",
+  "version": "2.0.0",
   "description": "Webpack loader for `NgModule` lazy loading using the angular router",
   "author": "Shlomi Assaf <shlomiasaf@gmail.com>",
   "license": "MIT",

src/builtin_codegens.ts

@@ -6,7 +6,7 @@ function getRequireString(file: string, module: string): string {
 }
 
 export const syncCodeGen: LoaderCodeGen =
-  (file: string, module: string) => `loadChildren: () => ${getRequireString(file, module)}`;
+  (file: string, module: string) => `loadChildren: function() { return ${getRequireString(file, module)}; }`;
 
 export const ensureCodeGen: LoaderCodeGen = (file: string, module: string,
                                              loaderOptions: RouterLoaderOptions,
@@ -15,27 +15,43 @@ export const ensureCodeGen: LoaderCodeGen = (file: string, module: string,
   const webpackChunkName = resourceOptions.chunkName ? `, '${resourceOptions.chunkName}'` : '';
 
   const result = [
-    `loadChildren: () => new Promise(function (resolve) {`,
-    `  (require as any).ensure([], function (require: any) {`,
+    `loadChildren: function() { return new Promise(function (resolve) {`,
+    `  require.ensure([], function (require) {`,
     `    resolve(${requireString});`,
     `  }${webpackChunkName});`,
-    `})`
+    `})}`
   ];
 
   return loaderOptions.inline ? result.join('') : result.join('\n');
 };
 
 export const systemCodeGen: LoaderCodeGen = (file: string, module: string, opts: RouterLoaderOptions) => {
+  systemCodeGen['deprecated']();
   const result = [
-    `loadChildren: () => System.import('${file}')`,
-    `  .then( (module: any) => module['${module}'] )`
+    `loadChildren: function() { return System.import('${file}')`,
+    `.then( function(module) { return module['${module}']; } ); }`
   ];
 
   return opts.inline ? result.join('') : result.join('\n');
 };
+systemCodeGen['deprecated'] = () => {
+  console.warn('\nDEPRECATED: ng-router-loader "async-system" loader use the System.import construct which is deprecated in webpack 2 and will be removed in webpack 3, please use the "async-import" instead. (https://github.com/webpack/webpack/releases/tag/v2.1.0-beta.28)\n');
+  systemCodeGen['deprecated'] = () => {};
+};
+
+export const importCodeGen: LoaderCodeGen = (file: string, module: string, opts: RouterLoaderOptions) => {
+  const result = [
+    `loadChildren: function() { return import('${file}')`,
+    `  .then( function(module) { return module['${module}']; } ); }`
+  ];
+
+  return opts.inline ? result.join('') : result.join('\n');
+};
+
 
 export const BUILT_IN_CODEGENS: Array<{ name: string, codeGen: LoaderCodeGen }> = [
   { name: 'sync', codeGen: syncCodeGen },
   { name: 'async-require', codeGen: ensureCodeGen },
+  { name: 'async-import', codeGen: importCodeGen },
   { name: 'async-system', codeGen: systemCodeGen }
 ];

test/test.spec.ts

@@ -2,7 +2,7 @@ import * as Path from 'path';
 import { expect } from 'chai';
 import '../index'; // this will load the built in code generators.
 import * as options from '../src/options';
-import { syncCodeGen, ensureCodeGen, systemCodeGen } from '../src/builtin_codegens';
+import { syncCodeGen, ensureCodeGen, systemCodeGen, importCodeGen } from '../src/builtin_codegens';
 import { Loader, ReplaceResult } from '../src/Loader';
 import { wpFactory, WebpackMockFactory } from './testing/WebpackMock';
 
@@ -394,6 +394,19 @@ describe('Loader', () => {
         });
     });
 
+    it('should output async-import codegen', () => {
+      const loader = factory
+        .setOption('loader', 'async-import')
+        .toLoader();
+
+      return loader.replace(`loadChildren: 'app/module-container/child-module#ChildModule'`)
+        .then(mapToZero)
+        .then( (result: ReplaceResult) => {
+          expect(result.replacement).to.eql(importCodeGen(result.filePath, result.moduleName, loader.query, result.resourceQuery));
+        });
+    });
+
+
     it('should output a custom codegen', () => {
       const loader = factory.toLoader();
       function custom(file: string, module: string): string {