What Is Promise In Angular?

In this blog, you will learn what is promise in angular.

In Angular, a Promise is a JavaScript object that represents the eventual completion (or failure) of an asynchronous operation and allows us to handle the result when it becomes available.

Promises are used extensively in Angular to handle asynchronous operations such as HTTP requests, where we don't know when the server will respond, and we don't want to block the UI while waiting for a response.

Here's an example of using a Promise in Angular to make an HTTP request:

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
    selector: 'app-root',
    template: '<h1>{{data}}</h1>'
})
export class AppComponent implements OnInit {
    data: string;
    constructor(private http: HttpClient) {}
    ngOnInit() {
        this.http.get('https://jsonplaceholder.typicode.com/todos/1').toPromise().then((response) => {
            this.data = response['title'];
        }).catch((error) => {
            console.log(error);
        });
    }
}

In this example, we're using the HttpClient service from the @angular/common/http module to make an HTTP GET request to a JSON placeholder API. We're then calling the toPromise() method to convert the Observable returned by the get() method into a Promise. Finally, we're using the .then() and .catch() methods to handle the response and any errors that may occur.

The then() the method is called when the Promise is resolved (i.e., when we receive a response from the server), and the catch() method is called when the Promise is rejected (i.e., when there is an error). In this example, we're setting the data property of the component to the title property of the response object, which we receive from the server.