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Asynchronous Programming in Angular Promises vs. Observables

Asynchronous programming plays a crucial role in modern web development, especially in Angular applications where data fetching, event handling, and other operations often occur asynchronously. In Angular, two primary mechanisms for handling asynchronous operations are promises and observables. In this article, we'll delve into the differences between promises and observables, their usage, and provide code examples to illustrate their behavior.

Promises

Promises are a built-in feature of JavaScript that represent a single value that may be available now, or in the future, or never. They are used extensively in Angular for handling asynchronous operations such as HTTP requests. Let's consider a simple example of fetching data from an API using promises:

import { HttpClient } from '@angular/common/http';

constructor(private http: HttpClient) {}

getData(): Promise<any> {
  return this.http.get<any>('https://dummyjson.com/products').toPromise();
}

fetchData(): void {
  this.getData()
    .then(response => {
      console.log('Data received:', response);
    })
    .catch(error => {
      console.error('Error fetching data:', error);
    });
}

In the above code, the getData method returns a promise that resolves with the response from the API call. We then use the then method to handle the successful resolution of the promise and the catch method to handle any errors.

Observables

Observables are a more powerful abstraction for handling asynchronous operations in Angular. They represent a stream of values that arrive over time, making them suitable for scenarios such as handling user input events or real-time data streams. Let's rewrite the previous example using observables:

import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

constructor(private http: HttpClient) {}

getData(): Observable<any> {
  return this.http.get<any>('https://dummyjson.com/products');
}

fetchData(): void {
  this.getData().subscribe({
    next: response => {
      console.log('Data received:', response);
    },
    error: error => {
      console.error('Error fetching data:', error);
    }
  });
}

In this code, the getData method returns an observable that emits the response from the API call. We use the subscribe method to subscribe to the observable and define callback functions for handling the emitted values and errors.

GitHub Project Url: https://github.com/SardarMudassarAliKhan/CompleteUnderStandingOfAngular

Conclusion

In Angular, both promises and observables are used for handling asynchronous operations, but they differ in behavior and usage. Promises are simpler and more straightforward for handling basic asynchronous tasks with single values, while observables offer more flexibility and power, especially for handling complex asynchronous scenarios and dealing with streams of data over time. When choosing between promises and observables in Angular, consider the specific requirements and complexity of the asynchronous task at hand to determine which mechanism is more suitable for your needs.


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