Angular pluggable architecture?

Pluggable Architecture – A Software Architecture that allows to plug functionality using PluggableModules. Ward Cunningham

One of the projects I am involved in these days is composed of multiple applications each of them with its own front-end implemented in Angular, all using consistent UX patterns and framework. The common user flows like managing projects or navigating to the applications is handled in a central application. At the same time, common components like navbar or sidebars are reused across.

This front-end separation by applications or large features has prevented us from creating a big monolithic web app and our teams have the kind of independence and control in the front-end we get in the back-end with micro-services.

All good so far, but let’s say that now we want to have a dashboard application composed of widgets and one of the requirements is that multiple teams can implement and deploy their own widgets independently. Hence, without the need of modifying the dashboard application code or redeploying it when a new widget comes or gets updated.

Can an Angular CLI application load and render external widgets at runtime?

The short answer is yes, it is possible. You can find a working demo in this repo

The long answer is that there is not a straightforward solution ;-), it took me a little bit of research to find out how.

First of all, the application needs a way to load remote widget bundles at runtime. This sounds like lazy loading, but that is not going to help us, lazy loading is for loading modules linked to child routes, but the modules still need to belong to the same application and be known at build-time.

The solution is to use SystemJS, but only at runtime and only to load the widgets. We do not need to configure our CLI project to switch from Webpack to SystemJS.

Loading a bundle will look like this:

const module = await SystemJS.import('/path-to-a-module-bundle');

The next problem is that the bundle contains a Module and a Component for the widget but they have dependencies themselves to other modules. The smallest component has at least dependencies to @angular/core.

import { Component, OnInit } from '@angular/core';

To stop SystemJS from trying to find and fetch those vendor modules from the network we need to set SystemJS with the modules already available.

 * Set existing vendor modules into SystemJS registry.
 * This way SystemJS won't make HTTP requests to fetch imported modules
 * needed by the dynamicaly loaded Widgets.
import { System } from 'systemjs';
declare const SystemJS: System;

import * as angularCore from '@angular/core';
import * as angularCommon from '@angular/common';
import * as angularCommonHttp from '@angular/common/http';

SystemJS.set('@angular/core', SystemJS.newModule(angularCore));
SystemJS.set('@angular/common', SystemJS.newModule(angularCommon));
SystemJS.set('@angular/common/http', SystemJS.newModule(angularCommonHttp));

The second part is compiling and rendering each widget. For this, we need to make use of the Angular JIT compiler to compile the Angular module and component of the widget. And then create the widget component in ViewChield target div.

  selector: 'app-dashboard',
  template: '<div #content></div>'
export class DashboardComponent implements AfterViewInit {

  @ViewChild('content', { read: ViewContainerRef }) content: ViewContainerRef;

  constructor(private compiler: Compiler, private dashboardService: DashboardService,
    private injector: Injector) { }

  ngAfterViewInit() {

  private async loadWidgets() {
    const widgets = await this.dashboardService.getWidgetConfigs().toPromise();
    widgets.forEach((widget) => this.createWidget(widget));

  private async createWidget(widget: WidgetConfig) {
    // import external module bundle
    const module = await SystemJS.import(widget.moduleBundlePath);

    // compile module
    const moduleFactory = await this.compiler.compileModuleAsync(module[widget.moduleName]);

    // resolve component factory
    const moduleRef = moduleFactory.create(this.injector);
    const componentProvider = moduleRef.injector.get(;
    const componentFactory = moduleRef.componentFactoryResolver.resolveComponentFactory(componentProvider);

    // compile component


Note that to be able to use the JIT compiler our build needs to have AOT disabled what it is not ideal. There is an open issue ( to allow the use of the compiler with AOT, I tried some of the temporal solutions suggested like defining custom providers for JIT in the app module but I could not make it work yet.

– Developing with Angular, Denys Vuika.
– As busy as a bee — lazy loading in the Angular CLI, David Herges … how does lazy loading in the Angular CLI work under the hood?
– How to load dynamic external components into Angular application?
– Here is what you need to know about dynamic components in Angular, Maxim Koretskyi
– Modules are not what you think they are, Maxim Koretskyi
– Extension mechanism demo
– JIT Compiler needed with AOT Build for Dynamic Component.


Developing with a Stub backend on Angular 2

In Angular 1 I always use during development a stub or mock REST API backend that allows me running the application without the real API. In this way, the front-end implementation can be started before or in parallel with the backend. It is also useful for small prototypes or demos.

You could quickly implement a fake backend using Node or something similar, but I recommend to mock the backend directly in Angular. It is faster because the application won’t hit the wire and what I really like is that it is stateless (every time the browser is reloaded the stub data is reinitialized).

Those two points are great for local development but what I find fundamental is to use it for running protractor E2E tests, that way I always can rely on a backend substitute that does not keep state between test (protractor reloads the browser before every test, and again the stub data gets reinitialized).

This post shows how to configure a stub backend on Angular 2 using the MockBackend test class.
On develop mode we will override the Http provider to, instead of using a real backend implementation such as XHRBackend, use the MockBackend.

I define the stub backend provider in a separate file stub-backend-provider.ts, here is all the magic happens swapping the backend provider for develop mode and defining stub responses for determined HTTP requests.


import { Http, BaseRequestOptions, Response, ResponseOptions, RequestMethod, XHRBackend } from '@angular/http';
import { MockBackend, MockConnection } from '@angular/http/testing';

import { environment } from '../../environments/environment';
import { Task } from '../tasks-list/task';
import { generateUuid, getUuidFromUrl } from './stub-backend-utils';

 * Provider to allow the use of a stub backend instead of a real Http service for backend-less development.
export let stubBackendProvider = {
  provide: Http,
  deps: [MockBackend, BaseRequestOptions, XHRBackend],
  useFactory: (mockBackend: MockBackend, options: BaseRequestOptions, realBackend: XHRBackend) => {

    if (!environment.stubBackend) {
      console.log('Configuring real Http backend...');
      return new Http(realBackend, options);

    console.log('Configuring stub Http backend...');

    let tasks: Task[] = [
      {id: '9509c8b4-ad34-4378-b49c-c9206dfd7f75', name: 'Buy milk', done: false, userId: 'user-1'},
      {id: '1b35d8f8-9e80-4316-b3e3-135a8f81200f', name: 'Pay rent', done: true, userId: 'user-1'}];

    mockBackend.connections.subscribe((connection: MockConnection) => {

      // wrap in timeout to simulate server api call
      setTimeout(() => {

        // Get all tasks
        if (connection.request.method === RequestMethod.Get && connection.request.url.match('/tasks$')) {
          connection.mockRespond(new Response(new ResponseOptions({body: tasks.slice()})));

        // Save task
        if (connection.request.method === RequestMethod.Post && connection.request.url.match('/tasks$')) {
          let newTask = JSON.parse(connection.request.getBody());
 = generateUuid();

          connection.mockRespond(new Response(new ResponseOptions({body: newTask})));

        // Delete task
        if (connection.request.method === RequestMethod.Delete && connection.request.url.match('/tasks/*')) {
          let id = getUuidFromUrl(connection.request.url);
          tasks = tasks.filter(task => !== id);

          connection.mockRespond(new Response(new ResponseOptions()));
      }, 500);


    return new Http(mockBackend, options);

The provider requires uses a new Angular CLI environment property that I called stubBackend, with a value of true on develop and false on production.

export const environment = {
  production: false,
  stubBackend: true


export const environment = {
  production: false,
  stubBackend: false

Continue reading “Developing with a Stub backend on Angular 2”

Unit test Http Services on Angular 2

Angular 2 testing documentation is more than good, but I believe that it is missing a crucial bit. How should we test services that make use of Http?

For example, let’s say that we want to unit test a TasksService with a getTasks method to GET task resources from a REST API.

import { Injectable } from '@angular/core';
import { Http } from '@angular/http';
import 'rxjs/add/operator/toPromise';
import { Task } from './task';

export class TasksService {
  private tasksUrl = '';

  constructor(private http: Http) {}

  getTasks(): Promise<Task[]> {
    return this.http.get(this.tasksUrl)
      .then(response => response.json() as Task[]);

The service uses angular Http service to perform HTTP requests. Unit test of this service should be done in isolation because we don´t want our service to be hitting the real network and at the same time, we want to control and fake the responses from the API. For that reason, we need to use a mock Http service.

Implementing a fake version of the Http service can get really complicated, the good thing is that Angular 2 already provides one for us, the MockBackend.

This is a full example of unit test using MockBackend and BaseRequestOptions to create a Http mock.

import { TestBed, inject, tick, fakeAsync } from '@angular/core/testing';
import { BaseRequestOptions, Http, ConnectionBackend, Response, ResponseOptions, RequestMethod } from '@angular/http';
import { MockBackend } from '@angular/http/testing';

import { TasksService } from './tasks.service';
import { Task } from './task';

describe('TasksService', () => {

  const TASKS: Task[] = [
    {id: 'task-1', name: 'Buy milk', done: false, userId: 'user-1'},
    {id: 'task-2', name: 'Pay rent', done: true, userId: 'user-1'}

  beforeEach(() => {
      providers: [
          provide: Http,
          deps: [MockBackend, BaseRequestOptions]
          useFactory: (backend: ConnectionBackend, defaultOptions: BaseRequestOptions) => {
          return new Http(backend, defaultOptions);
        {provide: MockBackend, useClass: MockBackend},
        {provide: BaseRequestOptions, useClass: BaseRequestOptions},
        {provide: TasksService, useClass: TasksService}

  describe('getTasks()', () => {

    it('should return all tasks', inject([TasksService, MockBackend], fakeAsync((tasksService: TasksService, mockBackend: MockBackend) => {
      let result;

      mockBackend.connections.subscribe(c => {
        let response = new ResponseOptions({body: TASKS});
        c.mockRespond(new Response(response));

      tasksService.getTasks().then(tasks => {
        result = tasks;




As a reference, in Angular 1 we use the $httpBackend service mock.

    describe('getTasks()', function () {
        it('should return all tasks', function () {

            let tasks = TasksService.getTasks();
            tasks = resolvePromise(tasks, $q, $scope);



Deploy Angular 2 CLI app to Heroku

Angular2 CLI generated apps can’t be directly deployed in Heroku. But it is easy to configure them to do that using scripts to build and serve the app.

I used angular-cli 1.0.0-beta.20-4 to generate and Angular2/Webpack app.
npm install -g angular-cli
ng new ng2-demo-app

And configured the package.json file using heroku-prebuild, heroku-postbuild and start scripts to build the app and serve it using http-server.

"scripts": {
  "heroku-prebuild": "npm install -g http-server",
  "heroku-postbuild": "ng build --prod",
  "start": "http-server dist/",

Heroku-prebuild and heroku-postbuild are Heroku-specific build steps, they are equivalent to the generic preinstall or postinstall but using them we avoid running those scripts locally.

In Heroku dev-dependencies are not installed by default, that means that to make the ng build script to work we need to move dev-dependency to the dependencies block.

"dependencies": {
  "@angular/common": "~2.1.0",
  "@angular/compiler": "~2.1.0",
  "@angular/core": "~2.1.0",
  "@angular/forms": "~2.1.0",
  "@angular/http": "~2.1.0",
  "@angular/platform-browser": "~2.1.0",
  "@angular/platform-browser-dynamic": "~2.1.0",
  "@angular/router": "~3.1.0",
  "core-js": "~2.4.1",
  "rxjs": "5.0.0-beta.12",
  "ts-helpers": "~1.1.1",
  "zone.js": "~0.6.23",

  // moved here these devDependencies
  "angular-cli": "1.0.0-beta.20-4",
  "@angular/compiler-cli": "~2.1.0",
  "@types/jasmine": "~2.2.30",
  "@types/node": "~6.0.42",
  "typescript": "~2.0.3"
"devDependencies": {
  "codelyzer": "~1.0.0-beta.3",
  "jasmine-core": "2.4.1",
  "jasmine-spec-reporter": "2.5.0",
  "karma": "1.2.0",
  "karma-chrome-launcher": "~2.0.0",
  "karma-cli": "~1.0.1",
  "karma-jasmine": "~1.0.2",
  "karma-remap-istanbul": "~0.2.1",
  "protractor": "4.0.9",
  "ts-node": "1.2.1",
  "tslint": "3.13.0",
  "webdriver-manager": "10.2.5"

Notice that it’s preferable to move only the dependencies you actually need for production builds. For that reason I moved only the dependencies required for the build but not the testing or linting dependencies.

If you don’t want to be moving dependencies it is possible to disable the production mode in the Heroku instance with
heroku config:set NPM_CONFIG_PRODUCTION=false
With this Heroku will install all dependencies, included the dev ones.

Another alternative to the http-server solution explained here is to use the NGINX and Heroku-buildpack-static.


Jasmine-Matchers – Adding more common matchers to Jasmine.

Jasmine-Matchers is a library of test assertion matchers for a range of common use-cases, to improve the readability of tests written using the Jasmine testing framework.


Install the package

npm install karma-jasmine-matchers --save-dev

And configure it in karma.conf in the frameworks section

frameworks: ['jasmine', 'jasmine-matchers’],

To use the additional matchers also in protractor e2e, protractor should be configured to import the ‘jasmine-expect’ module before the tests run. That can be done in the protractor.conf.js like this:

onPrepare: function () {
// Import additional jasmine matchers


The list of additional matchers is available here


Examples of unit test refactors using new matchers

– expect(clients.length).toBe(2);
+ expect(clients).toBeArrayOfSize(2);

and instead of failing like this
Expected 1 to be 2.
when it fails, the new matcher look like this:
Expected [ Object({ id: ‘client-id’, name: ‘A Client’ }) ] to be array of size 2.

– expect(vm.getCategory({})).toBe(‘’);
Expected ‘Test’ to be ‘’
+ expect(vm.getCategory({})).toBeEmptyString();
Expected ‘Test’ to be empty string.

– expect(‘’);
Expected ‘Test’ to be ‘’
+ expect(;;
Expected ‘Test’ to be empty string.

– expect(data).toEqual({});
Expected Object({ location: ‘’, username: ‘username’, password: ‘password’, directory: ‘test’ }) to equal Object({ }).
+ expect(data).toBeEmptyObject();
Expected Object({ location: ‘’, username: ‘username’, password: ‘password’, directory: ‘test’ }) to be empty object.

– expect(vm.showHelp).toBe(true);
Expected false to be true.
+ expect(vm.showHelp).toBeTrue();
Expected false to be true.


Decorating Angular $httpBackend service.

An example of how to ​decorate the angular $httpBackend mock server with custom logic. In this example, I log to console the request method and URL.

// Configure the Mock HTTP Backend
    .config(['$provide', function ($provide) {
        $provide.decorator('$httpBackend', angular.mock.e2e.$httpBackendDecorator);

// Decorate Mock HTTP Backend to log requests
    .config(function ($provide) {
        $provide.decorator('$httpBackend', function ($delegate) {
            let decoratedHttpBackend = function (method, url, data, callback, headers, timeout, withCredentials, responseType) {
                console.log(method + ' ' + url);

                return $, method, url, data, callback, headers, timeout, withCredentials, responseType);

            for (var key in $delegate) {
                if ($delegate.hasOwnProperty(key)) {
                    decoratedHttpBackend[key] = $delegate[key];

            return decoratedHttpBackend;