Angular Nx Tutorial - Step 7: Share Code

Awesome! The application is working end to end! However, there is a problem. Both the backend and the frontend define the Todo interface. The interface is in sync now, but in a real application, over time, it will diverge, and, as a result, runtime errors will creep in. You should share this interface between the backend and the frontend. In Nx, you can do this by creating a library.

Run the following command to create a library:

npx nx g @nrwl/workspace:lib data

The result should look like this:

myorg/
├── apps/
│   ├── todos/
│   ├── todos-e2e/
│   └── api/
├── libs/
│   └── data/
│       ├── src/
│       │   ├── lib/
│       │   │   ├── data.spec.ts
│       │   │   └── data.ts
│       │   └── index.ts
│       ├── .babelrc
│       ├── .eslintrc.json
│       ├── jest.config.js
│       ├── project.json
│       ├── README.md
│       ├── tsconfig.json
│       ├── tsconfig.lib.json
│       └── tsconfig.spec.json
├── tools/
├── angular.json
├── nx.json
├── package.json
└── tsconfig.base.json

Copy the interface into libs/data/src/lib/data.ts.

1export interface Todo {
2  title: string;
3}

A note about VS Code :

If you're using VS Code it may be necessary at this point to restart the TS server so that the new @myorg/data package is recognized. This may need to be done every time a new workspace library is added. If you install the Nx Console extension you won't need to take this step.

Refactor the API

Now update apps/api/src/app/app.service.ts to import the interface:

1import { Injectable } from '@nestjs/common';
2import { Todo } from '@myorg/data';
3
4@Injectable()
5export class AppService {
6  todos: Todo[] = [{ title: 'Todo 1' }, { title: 'Todo 2' }];
7
8  getData(): Todo[] {
9    return this.todos;
10  }
11
12  addTodo() {
13    this.todos.push({
14      title: `New todo ${Math.floor(Math.random() * 1000)}`,
15    });
16  }
17}

Update the Angular application

Next import the interface in apps/todos/src/app/app.component.ts:

1import { Component } from '@angular/core';
2import { HttpClient } from '@angular/common/http';
3import { Todo } from '@myorg/data';
4
5@Component({
6  selector: 'myorg-root',
7  templateUrl: './app.component.html',
8  styleUrls: ['./app.component.css'],
9})
10export class AppComponent {
11  todos: Todo[] = [];
12
13  constructor(private http: HttpClient) {
14    this.fetch();
15  }
16
17  fetch() {
18    this.http.get<Todo[]>('/api/todos').subscribe((t) => (this.todos = t));
19  }
20
21  addTodo() {
22    this.http.post('/api/addTodo', {}).subscribe(() => {
23      this.fetch();
24    });
25  }
26}

Every time you add a new library, you have to restart npx nx serve.

Restart the api and application in separate terminal windows

npx nx serve api
npx nx serve todos

And you should see the application running.

What's Next