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This posts shows an example of how to implement a fake or mock backend in Angular 2 and TypeScript.

A mock backend is used for doing backendless development in Angular 2 which allows you can demo your code without the need to create a backend server api, it's perfect for code hosted in Plunker which doesn't have a backend. The MockBackend class is also used for unit testing but I won't be focusing on that here.

I created the below fake backend as part of an Angular 2 User Registration and Login Example & Tutorial that I wrote a couple of months ago and includes mock endpoints for authentication and user management, it uses browser local storage to store data so it can behave just like a real api including data persistance.

Pass Through Unmocked Requests to Real Backend

Sometimes there's a need to pass through specific requests to the server instead of being caught by the MockBackend, in Angular 1 you could pass through certain URLs with a call to $httpBackend.whenGET(...).passThrough(); .

However there isn't a passThrough method on the the Angular 2 MockBackend class, the way I got around this is by including the real XHRBackend as a dependency to my fake backend provider, then using the real backend to perform an http request to the server for any URLs that aren't handled by a mock response. You can see the code for passing through requests at the bottom of the code sample below.

Angular 2 Fake Backend Provider

import { Http, BaseRequestOptions, Response, ResponseOptions, RequestMethod, XHRBackend, RequestOptions } from '@angular/http'; import { MockBackend, MockConnection } from '@angular/http/testing'; export function fakeBackendFactory(backend: MockBackend, options: BaseRequestOptions, realBackend: XHRBackend) { // array in local storage for registered users let users: any[] = JSON.parse(localStorage.getItem('users')) || []; // configure fake backend backend.connections.subscribe((connection: MockConnection) => { // wrap in timeout to simulate server api call setTimeout(() => { // authenticate if (connection.request.url.endsWith('/api/authenticate') && connection.request.method === RequestMethod.Post) { // get parameters from post request let params = JSON.parse(connection.request.getBody()); // find if any user matches login credentials let filteredUsers = users.filter(user => { return user.username === params.username && user.password === params.password; }); if (filteredUsers.length) { // if login details are valid return 200 OK with user details and fake jwt token let user = filteredUsers[0]; connection.mockRespond(new Response(new ResponseOptions({ status: 200, body: { id: user.id, username: user.username, firstName: user.firstName, lastName: user.lastName, token: 'fake-jwt-token' } }))); } else { // else return 400 bad request connection.mockError(new Error('Username or password is incorrect')); } return; } // get users if (connection.request.url.endsWith('/api/users') && connection.request.method === RequestMethod.Get) { // check for fake auth token in header and return users if valid, this security is implemented server side in a real application if (connection.request.headers.get('Authorization') === 'Bearer fake-jwt-token') { connection.mockRespond(new Response(new ResponseOptions({ status: 200, body: users }))); } else { // return 401 not authorised if token is null or invalid connection.mockRespond(new Response(new ResponseOptions({ status: 401 }))); } return; } // get user by id if (connection.request.url.match(/\/api\/users\/\d+$/) && connection.request.method === RequestMethod.Get) { // check for fake auth token in header and return user if valid, this security is implemented server side in a real application if (connection.request.headers.get('Authorization') === 'Bearer fake-jwt-token') { // find user by id in users array let urlParts = connection.request.url.split('/'); let id = parseInt(urlParts[urlParts.length - 1]); let matchedUsers = users.filter(user => { return user.id === id; }); let user = matchedUsers.length ? matchedUsers[0] : null; // respond 200 OK with user connection.mockRespond(new Response(new ResponseOptions({ status: 200, body: user }))); } else { // return 401 not authorised if token is null or invalid connection.mockRespond(new Response(new ResponseOptions({ status: 401 }))); } return; } // create user if (connection.request.url.endsWith('/api/users') && connection.request.method === RequestMethod.Post) { // get new user object from post body let newUser = JSON.parse(connection.request.getBody()); // validation let duplicateUser = users.filter(user => { return user.username === newUser.username; }).length; if (duplicateUser) { return connection.mockError(new Error('Username "' + newUser.username + '" is already taken')); } // save new user newUser.id = users.length + 1; users.push(newUser); localStorage.setItem('users', JSON.stringify(users)); // respond 200 OK connection.mockRespond(new Response(new ResponseOptions({ status: 200 }))); return; } // delete user if (connection.request.url.match(/\/api\/users\/\d+$/) && connection.request.method === RequestMethod.Delete) { // check for fake auth token in header and return user if valid, this security is implemented server side in a real application if (connection.request.headers.get('Authorization') === 'Bearer fake-jwt-token') { // find user by id in users array let urlParts = connection.request.url.split('/'); let id = parseInt(urlParts[urlParts.length - 1]); for (let i = 0; i < users.length; i++) { let user = users[i]; if (user.id === id) { // delete user users.splice(i, 1); localStorage.setItem('users', JSON.stringify(users)); break; } } // respond 200 OK connection.mockRespond(new Response(new ResponseOptions({ status: 200 }))); } else { // return 401 not authorised if token is null or invalid connection.mockRespond(new Response(new ResponseOptions({ status: 401 }))); } return; } // pass through any requests not handled above let realHttp = new Http(realBackend, options); let requestOptions = new RequestOptions({ method: connection.request.method, headers: connection.request.headers, body: connection.request.getBody(), url: connection.request.url, withCredentials: connection.request.withCredentials, responseType: connection.request.responseType }); realHttp.request(connection.request.url, requestOptions) .subscribe((response: Response) => { connection.mockRespond(response); }, (error: any) => { connection.mockError(error); }); }, 500); }); return new Http(backend, options); }; export let fakeBackendProvider = { // use fake backend in place of Http service for backend-less development provide: Http, useFactory: fakeBackendFactory, deps: [MockBackend, BaseRequestOptions, XHRBackend] };



Hooking up the Fake Backend to your Project

To add the fake backend provider to your project you need to import the fakeBackendProvider, MockBackend, MockConnection and BaseRequestOptions in your app module as shown below, and also add the fakeBackendProvider, MockBackend and BaseRequestOptions to the list of providers in your app module.

Below is the complete app module code for the example where the fake backend is used, for the full example and demo plunk check out http://jasonwatmore.com/post/2016/09/29/angular-2-user-registration-and-login-example-tutorial