Reactive Programming in Angular

Reactive programming is a programming paradigm that deals with asynchronous data streams and propagates change, which is especially useful for building complex and event-driven user interfaces. In Angular, reactive programming can be done using RxJS library, which provides powerful operators to manipulate data streams.

Syntax

import { Observable, Subject } from 'rxjs';

// Creating an observable
const observable$ = new Observable(observer => {
  observer.next('Hello');
  observer.next('World');
});

// Creating a subject
const subject$ = new Subject();

// Subscribe to an observable or a subject
observable$.subscribe(data => console.log(data));
subject$.subscribe(data => console.log(data));

// Emit data to a subject
subject$.next('Emitting some data');

Example

<input type="text" [formControl]="search" />
<ul>
  <li *ngFor="let item of items$ | async">{{ item }}</li>
</ul>

import { Component } from '@angular/core';
import { FormControl } from '@angular/forms';
import { Observable } from 'rxjs';
import { debounceTime, distinctUntilChanged, switchMap } from 'rxjs/operators';

@Component({
  selector: 'app-search',
  template: `
    <input type="text" [formControl]="search" />
    <ul>
      <li *ngFor="let item of items$ | async">{{ item }}</li>
    </ul>
  `,
})
export class SearchComponent {
  search = new FormControl();
  items$: Observable<string[]>;

  constructor(private searchService: SearchService) {
    this.items$ = this.search.valueChanges.pipe(
      debounceTime(300),
      distinctUntilChanged(),
      switchMap(term => this.searchService.search(term)),
    );
  }
}

Output

The above example will produce a search box and a list of items. As the user types in the search box, an HTTP request is made to the server to fetch the matching items and display them on the screen.

Explanation

In the above example, we used reactive programming to create a search box that fetches data from the server and displays it on the screen as the user types. Here, FormControl is used to track changes in the input field, and valueChanges is used to create an observable that emits the current value of the input field. We then use RxJS operators like debounceTime, distinctUntilChanged, and switchMap to manipulate the data stream and make an HTTP request to the server whenever the user types.

Use

Reactive programming in Angular is especially useful for handling complex and asynchronous data flows. It can be used for:

• Building event-driven user interfaces
• Fetching data from the server and displaying it on the screen
• Managing state in large-scale applications
• Handling user interactions and side-effects

Important Points

• Reactive programming in Angular is done using RxJS library.
• RxJS provides powerful operators to manipulate data streams and handle complex asynchronous flows.
• Reactive programming can help to manage complexity and build event-driven user interfaces.

Summary

Reactive programming is a powerful paradigm for building complex and event-driven user interfaces in Angular. It can be done using RxJS library, which provides powerful operators to manipulate data streams. Reactive programming can help to manage complexity and handle complex asynchronous flows.