Connect Angular application with ReactJS app?

Question

I have a Angular app and some part of application I want write in ReactJS.

How can I inject ReactJS app into existing Angular application? I need also bidirectional communication for components.

Answer 1

INTRO: You can have different environments, different use cases, and different needs. Please remember that there are only some approaches to this solution that can just trigger you to invent something different - a better suited for your use case.

Two different solutions with example:

• Angular-ReactJS without communication
• Angular-ReactJS with bidirectional communication

All code below is minimal to show a problem on a presented step. On GitHub, you have a complete code to solve a problem, not always 1:1 with the example below because this code is extended.

Angular-ReactJS without communication

To add ReactJS app into existing Angular application you need to install 5 npm dependencies: react, react-dom:

npm install --save react
npm install --save react-dom
npm install --save-dev @types/react
npm install --save-dev @types/react-dom
npm install --save-dev @types/react-select

Next step - we should permit to use jsx template in .tsx files, so we should edit tsconfig.json, and add:

{
    ...
   "compilerOptions": {
    …
    "jsx": "react"
}

If you use WebStorm you should restart your project because a TSLint shows an error till restart.

To keep a clear structure, I create this structure of directory:

angular /
  ng-hero.component.ts // Component in Angular
  react-renderer.component.ts // ReactJS renderer without communication
react /
  react-application.tsx // React init application
  react-hero.tsx // React hero component
app.component.html
app.component.ts

Now you need to create a special component in Angular, which will be responsible for embedding the ReactJS application. This component I will call ReactRendererComponent. This component is very simple and it has only one template line, a constructor with import Injector and one line in ngOnInit:

@Component({
  selector: 'app-react-renderer',
  template: `<div class="react-container" id="react-renderer"></div>`
})
export class ReactRendererComponent implements OnInit {
  constructor(public injector: Injector) { }

  ngOnInit() {
    ReactApplication.initialize('react-renderer', this.injector);
  }
}

Now we need ReactApplication component where we initialize the ReactJS app:

interface IReactApplication {
  injector: Injector;
}

class ReactApp extends React.Component<IReactApplication, any> {
  constructor(props) {
    super(props);
  }

  render() {
    return (
      <div className={'renderer'}>
        <h2>ReactJS component: </h2>
        <br/>
        <ReactHero/>
      </div>
    );
  }
}

export class ReactApplication {

  static initialize(
    containerId: string,
    injector: Injector
  ) {
    ReactDOM.render(
      <ReactApp injector={injector}/>,
      document.getElementById(containerId)
    );
  }
}

And we need ReactHero component which was used in the example below:

class ReactHero extends React.Component<any, any> {

  constructor(props) {
    super(props);
  }

  render() {
    return (
      <span>
        <span>react-hero works!</span><br/>
        <span>Don't have any data</span>
      </span>
    );
  }
}
export default ReactHero;

In Angular App we should use ReactRenderer component, so we use:

App.component data:
<hr>
<h2>This is Angular</h2>
<img width="100" alt="Angular Logo" src="data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHZpZXdCb3g9IjAgMCAyNTAgMjUwIj4KICAgIDxwYXRoIGZpbGw9IiNERDAwMzEiIGQ9Ik0xMjUgMzBMMzEuOSA2My4ybDE0LjIgMTIzLjFMMTI1IDIzMGw3OC45LTQzLjcgMTQuMi0xMjMuMXoiIC8+CiAgICA8cGF0aCBmaWxsPSIjQzMwMDJGIiBkPSJNMTI1IDMwdjIyLjItLjFWMjMwbDc4LjktNDMuNyAxNC4yLTEyMy4xTDEyNSAzMHoiIC8+CiAgICA8cGF0aCAgZmlsbD0iI0ZGRkZGRiIgZD0iTTEyNSA1Mi4xTDY2LjggMTgyLjZoMjEuN2wxMS43LTI5LjJoNDkuNGwxMS43IDI5LjJIMTgzTDEyNSA1Mi4xem0xNyA4My4zaC0zNGwxNy00MC45IDE3IDQwLjl6IiAvPgogIDwvc3ZnPg==">
<hr>

<!-- Without data binding -->
<app-react-renderer></app-react-renderer>

At this moment we have an Angular app with an embedded ReactJS app, but without any communication. Is it enough for you? If yes, it's all. If you need any kind of communication between both applications, I present you the RxJS option below.

Angular-ReactJS with bidirectional communication

In this example, you have bidirectional data binding supported by RxJS. You can get this data, and use them in your ReactJS app and Angular app to see all changes. This is enough for a lot of projects, but you can use different options to get this bidirectional communication, for example, you can use Redux for them.

To keep it clear, below I present a complete directory structure for this part:

angular /
  hero.service.ts
  ng-hero.component.ts // Component in Angular
  react-bidirectional-renderer.component.ts // ReactJS renderer with bidirectional communication
model /
  hero.ts // interface for Hero object
react-bidirectional
  react-bidirectional-application.tsx // React init application with bidirectional communication
  react-bidirectional-hero.tsx // React hero component with RxJS support
app.component.html
app.component.ts

First of all, we create IHero interface with data: /model/hero.ts

export interface IHero {
  name: string;
  age: number;
}

In the next step we create angular/hero.service.ts service, to use it in the Angular part of application:

@Injectable({
  providedIn: 'root'
})
export class HeroService {
  private heroes$: BehaviorSubject<IHero[]> = new BehaviorSubject([]);

  constructor() {
  }

  addHeroes(hero: IHero) { // To add new hero
    const actualHero = this.heroes$.value;
    actualHero.push(hero);
    this.heroes$.next(actualHero);
  }

  updateHeroAge(heroId: number, age: number) { // To update age of selected hero
    const actualHero = this.heroes$.value;
    actualHero[heroId].age = age;
    this.heroes$.next(actualHero);
  }

  getHeroes$(): BehaviorSubject<IHero[]> { // To get BehaviorSubject and pass it into ReactJS
    return this.heroes$;
  }
}

And in app.component.ts we initialize with data (Zeus and Poseidon):

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html'
})
export class AppComponent implements OnInit {
  public heroesObj$: BehaviorSubject<IHero[]>;
  public heroes: IHero[];

  constructor(private heroService: HeroService) {}

  ngOnInit(): void {
    this.heroService.getHeroes$().subscribe((res: IHero[]) => {
      this.heroes = res;
    });

    this.heroesObj$ = this.heroService.getHeroes$();

    this.initHeroes();
  }

  initHeroes() {
    this.heroService.addHeroes({name: 'Zeus', age: 88});
    this.heroService.addHeroes({name: 'Poseidon', age: 46});
  }
}

In the next step we should prepare the ReacJS part of the application, so we create react-bidirectional/react-bidirectional-application.tsx file:

interface IReactBidirectionalApp {
  injector: Injector;
  heroes$: BehaviorSubject<IHero[]>; // We use this interface to grab RxJS object
}

class ReactBidirectionalApp extends React.Component<IReactBidirectionalApp, any> {
  constructor(props) {
    super(props);

    this.state = {
      heroes$: this.props.heroes$ // and we pass this data into ReactBidirectionalHero component
    };
  }

  render() {
    return (
      <div className={'renderer'}>
        <h2>ReactJS component (bidirectional data binding): </h2>
        <ReactBidirectionalHero heroes$={this.state.heroes$}/>
      </div>
    );
  }
}

export class ReactBidirectionalApplication {

  static initialize(
    containerId: string,
    injector: Injector,
    heroes$: BehaviorSubject<IHero[]>, // This is necessary to get RxJS object
  ) {
    ReactDOM.render(
      <ReactBidirectionalApp injector={injector} heroes$={heroes$}/>,
      document.getElementById(containerId)
    );
  }
}

In the next step we need ReactBidirectionalHero component, so we create it:

interface IReactBidirectionalHero {
  heroes$: BehaviorSubject<IHero[]>;
}

class ReactBidirectionalHero extends React.Component<IReactBidirectionalHero, any> {
  constructor(props) {
    super(props);

    this.state = {
      heroes: []
    };

    this.addAge = this.addAge.bind(this); // Register function to bump age
    this.addHero  = this.addHero.bind(this); // Register function to add new Hero
  }

  componentDidMount(): void {
    // In componentDidMount we subscribe heroes$ object
    this.props.heroes$.subscribe((res: IHero[]) => {
      // and we pass this data into React State object
      this.setState({heroes: res});
    });
  }

  addAge(i: number) {
    const temp = this.state.heroes;
    temp[i].age = temp[i].age + 1;

    // In this way we update RxJS object
    this.props.heroes$.next( temp);
  }

  addHero() {
    const temp = this.state.heroes;
    temp.push({name: 'Atena', age: 31});

    // In this way we update RxJS object
    this.props.heroes$.next(temp);
  }

  render() {
    // Hire we render RxJS part of application with addAge button and ADD ATENA button below
    const heroes = this.state.heroes.map((hero: IHero, i) => {
      return <span key={i}>{hero.name} - {hero.age} <button onClick={() => this.addAge(i)}>Add {hero.name} age</button><br/></span>;
    });
    return (
      <span>
        <span>react-hero works!</span><br/>
        {heroes}
        <br/>
        <button onClick={this.addHero}>ADD ATENA</button>
      </span>
    );
  }
}

export default ReactBidirectionalHero;

Now we need to initialize ReactJS app in Angular application, so we create angular/react-bidirectional-renderer.component.ts - it's very simple, with only one changes in comparison to version without communication:

@Component({
  selector: 'app-react-owc-renderer',
  template: `<div class="react-container" id="react-owc-renderer"></div>`
})
export class ReactBidirectionalRendererComponent implements OnInit {
  // Hire we get data from the parent component, but of course, we can also subscribe this data directly from HeroService if we prefer this way
  @Input() heroes$: BehaviorSubject<IHero[]>;

  constructor(public injector: Injector) { }

  ngOnInit() {
    // We add only one parameter into initialize function
    ReactBidirectionalApplication.initialize('react-owc-renderer', this.injector, this.heroes$);
  }
}

And now we should change a little ng-hero.component.ts to see all effect:

@Component({
  selector: 'app-ng-hero',
  template: `
    <div>
      <span>ng-hero works!</span><br/>
      <span *ngFor="let hero of heroes; let i = index;">{{hero.name}} - {{hero.age}} - <button (click)="addAge(i)">Add {{hero.name}} age</button><br/></span>
      <br/>
      <button (click)="addHero()">ADD AFRODITA</button>
    </div>
  `
})
export class NgHeroComponent implements OnInit {
  public heroes: IHero[];

  constructor(private heroService: HeroService) { }

  ngOnInit() {
    this.heroService.getHeroes$().subscribe((res: IHero[]) => {
      this.heroes = res;
    });
  }

  addAge(heroId: number) {
    this.heroService.updateHeroAge(heroId, this.heroes[heroId].age + 1);
  }

  addHero() {
    this.heroService.addHeroes({name: 'Afrodita', age: 23});
  }

}

Finally, we change app.component.html:

App.component data:
<hr>
<h2>This is Angular component: </h2>
<app-ng-hero></app-ng-hero>
<hr>

<!-- With bidirectional data binding-->
<app-react-owc-renderer [heroes$]="heroesObj$"></app-react-owc-renderer>
<hr>

And everything should work. If you have any problems, feel free to ask.

Complete repository with this solution you can find on GitHub.

If you look for a demo, click hire.

Some extra ideas

As you can see I introduce just two approaches to this problem. Here just some tips that could give you a wider view and give you some possibility to find your own better suit solutions for your use case.

• Store - share Store between Angular and React application by using Redux - this approach is really nice because you don't need to care about passing data between components. There are some potential problems with this approach - if React application modifies the store and you subscribe to those data please remember about potential problems with NG change detection. Data modified outside of Angular applications could be a problem in some cases so keep it in mind.
• Iframe - this is the simplest way to do any kind of just usage ReactJS component in Angular app without bidirectional communication. You can just pass some data in query params of the URL and render React component.
• Preact.js - this is really nice approach if you just would like to use a simple react component but you worry about bundle size. Preact gives a lot of React features but it is really small so your build and customer doesn't feel any influence on your technology mirage.