LoopBack 4 Todo Application Tutorial - Putting it all together
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Putting it all together

We’ve got all of our artifacts now, and all that’s left is to bind them to our Application so that LoopBack’s Dependency injection system can tie it all together for us!

LoopBack’s boot module will automatically discover our controllers, repositories, datasources and other artifacts and inject them into our application for use.

NOTE: The boot module will discover and inject artifacts that follow our established conventions for artifact directories. Here are some examples:

  • Controllers: ./src/controllers
  • Datasources: ./src/datasources
  • Models: ./src/models
  • Repositories: ./src/repositories

To find out how to customize this behavior, see the Booters section of Booting an Application.


import {ApplicationConfig} from '@loopback/core';
import {RestApplication, RestServer} from '@loopback/rest';
import {MySequence} from './sequence';
import {db} from './datasources/db.datasource';

/* tslint:disable:no-unused-variable */
// Binding and Booter imports are required to infer types for BootMixin!
import {BootMixin, Booter, Binding} from '@loopback/boot';

// juggler imports are required to infer types for RepositoryMixin!
import {
} from '@loopback/repository';
/* tslint:enable:no-unused-variable */

export class TodoListApplication extends BootMixin(
) {
  constructor(options?: ApplicationConfig) {

    // Set up the custom sequence

    this.projectRoot = __dirname;
    // Customize @loopback/boot Booter Conventions here
    this.bootOptions = {
      controllers: {
        // Customize ControllerBooter Conventions here
        dirs: ['controllers'],
        extensions: ['.controller.js'],
        nested: true,


  setupDatasources() {
    // This will allow you to test your application without needing to
    // use a "real" datasource!
    const datasource =
      this.options && this.options.datasource
        ? new juggler.DataSource(this.options.datasource)
        : db;

  async start() {
    await super.start();

    const server = await this.getServer(RestServer);
    const port = await server.get<number>('rest.port');
    console.log(`Server is running at${port}`);

Try it out

Let’s try out our application! First, you’ll want to start the app.

$ npm start
Server is running on port 3000

Next, you can use the API Explorer to browse your API and make requests!

Here are some requests you can try:

  • POST /todos with a body of { "title": "get the milk" }
  • GET /todos/{id} using the ID you received from your POST, and see if you get your Todo object back.
  • PATCH /todos/{id} with a body of { "desc": "need milk for cereal" }

That’s it! You’ve just created your first LoopBack 4 application!

More examples and tutorials

Eager to continue learning about LoopBack 4? Check out our examples and tutorials section to find examples for creating your own custom components, sequences and more!

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