Write and run a LoopBack 4 "Hello World" project in TypeScript.
Page Contents

Prerequisites

Install Node.js (version 8.9 or higher) if it is not already installed on your machine.

Install LoopBack 4 CLI

The LoopBack 4 CLI is a command-line interface that scaffolds a project or an extension by generating the basic code. The CLI provides the fastest way to get started with a LoopBack 4 project that adheres to best practices.

Install the CLI globally by running

npm i -g @loopback/cli

Create a new project

The CLI tool will scaffold the project, configure the TypeScript compiler, and install all the required dependencies. To create a new project, run the CLI as follows and answer the prompts.

lb4 app

Answer the prompts as follows:

? Project name: getting-started
? Project description: Getting started tutorial
? Project root directory: (getting-started)
? Application class name: StarterApplication
? Select features to enable in the project:
❯◉ Enable tslint
 ◉ Enable prettier
 ◉ Enable mocha
 ◉ Enable loopbackBuild
 ◉ Enable vscode
 ◉ Enable repositories
 ◉ Enable services

Starting the project

The project comes with a “ping” route to test the project. Let’s try it out by running the project.

cd getting-started
npm start

In a browser, visit http://127.0.0.1:3000/ping.

Adding your own controller

Now that we have a basic project created, it’s time to add our own controller. Let’s add a simple “Hello World” controller as follows:

lb4 controller

  • Answer the prompts as follows:

    ? Controller class name: hello
? What kind of controller would you like to generate? Empty Controller
  create src/controllers/hello.controller.ts
  update src/controllers/index.ts

Controller Hello was now created in src/controllers/

  • Paste the following contents into the file /src/controllers/hello.controller.ts:

    import {get} from '@loopback/rest';

export class HelloController {
  @get('/hello')
  hello(): string {
    return 'Hello world!';
  }
}

  • Start the application using npm start.

    • Note: If your application is still running, press CTRL+C to stop it before restarting it

  • Visit http://127.0.0.1:3000/hello to see Hello world!

Code sample

You can view the generated code for this example at: hello-world