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Developing Angular Apps without a Back End Using MockBackend

In this article, we show how to develop apps with the Angular 2 MockBackend class, providing a way for front-end teams to become independent of the back end, and a useful interface that reduces the risk of structural changes.

Getting your front-end and back-end teams up to full speed is certainly something each company is looking for. Often, though, teams fall into the pit of blocking dependencies. Those are situations where the upcoming work of one team is blocked by a user story owned by the other team.

One of those examples is the communication process between the front- and back-end. Over recent times, REST APIs have ascended the throne of so-called communication standards. The benefit of using JSON, a simple yet effective data transfer format, is that front-end workers don’t need to care about the actual back end anymore. Whatever crosses the wire is directly consumable and may be leveraged to bring data into your application. So it’s not surprising that those elementary entities often don’t get modeled at all on the front end and are consumed as they arrive. This brings us to the fundamental problem of having to wait for the back-end team to provide something useful. As depicted in the following figure, we see that both teams start in parallel, but at a certain time one team is kept waiting for the other to catch up.

Diagram showing how front-end tasks depend on the back-end team finishing the API

Besides this, having no kind of fixed structure makes each change a potentially dangerous one. So the focus of this article is to present a way that front-end teams can become independent of the back end and at the same time provide a useful interface which reduces the risk of structural changes.

This article has been updated in line with the recent release of version 2.1.2 of Angular. The linked Plunkr example app has also been updated.

A Ticketing System without a Real Back End

In order to achieve that independence, it’s imperative to start thinking upfront about your project. What entities are you going to use? What communication endpoints result therefore?

This can be done by creating a small table highlighting the necessary REST endpoints and describing their purpose. Remember the reason we’re doing that upfront is for both parties to agree upon a common structure for communication. That doesn’t mean it has to be perfectly done, but it should help you get started with the most important steps. As time passes, just update your interface accordingly with the new routes needed.

The actual process of creating a back-endless environment is to capture all HTTP requests and instead of letting them go out into the wild, and reply with a fake response containing the information we’d like to have. This article will demonstrate the approach by describing a simple ticketing system. It uses the endpoints shown in the following table.

Note that the example utilizes the POST verb for both the update and create route. Another option would be to leverage PUT for the update process. Keep in mind, though, that PUT should be idempotent, meaning every consecutive call has to produce the same result. Feel free to choose whatever suites your needs.

MethodRouteRequest bodyDescription
GET/ticketNoneRequest all tickets
GET/ticket/:idNoneRequest a single ticket via the provided :id parameter
POST/ticketTicket entityCreate a new or update an existing ticket
DELETE/ticket/:idNoneDelete a ticket, identified by the :id parameter

Table 1: Consumed endpoints of the ticketing system

The Ticket entity is a simple TypeScript class containing some basic ticket information:

export class Ticket {
  public _id: string;
  public title: string;
  public assignedTo: string;
  public description: string;
  public percentageComplete: number;

  constructor(id: string, title: string, assignedTo: string,
    description: string, percentageComplete: number) {
    this._id = id;
    this.title = title;
    this.assignedTo = assignedTo;
    this.description = description;
    this.percentageComplete = percentageComplete;

ticket.entity.ts describing the ticket entity

You may find the complete code as well as a preview for this example on Plunker:

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