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

Prerequisites

Install Node.js (version 8.x.x or higher) if not already installed on your machine.

Install LoopBack 4 CLI

The LoopBack 4 CLI is a command-line interface that can scaffold a project or extension with more features under development. 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 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 project build settings: Enable tslint, Enable prettier, Enable mocha, Enable loopbackBuild

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:

  • Create a new file in /src/controllers/ called hello.controller.ts.

  • Paste the following contents into the file:

    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!