What is RxJS and how is it used in Angular?

Q: What is RxJS and how is it used in Angular?

Learn the answer to "What is RxJS and how is it used in Angular?" with detailed explanations, code examples, and best practices on DeployU.

The Scenario

You are a frontend engineer at a social media company. You are building a new feature that needs to handle a stream of real-time data from a WebSocket.

You need to find a way to process the data as it comes in, and you are considering using RxJS.

The Challenge

Explain what RxJS is and how it is used in Angular. What are the key concepts of RxJS, and how would you use them to solve this problem?

Wrong Approach

A junior engineer might not be aware of RxJS. They might try to solve this problem by using a series of callbacks, which would be difficult to read and maintain.

Addresses symptoms, not root cause

Right Approach

A senior engineer would know that RxJS is the perfect tool for this job. They would be able to explain what RxJS is and how to use it to handle a stream of real-time data.

Step 1: Understand What RxJS Is

RxJS is a library for reactive programming using Observables, to make it easier to compose asynchronous or callback-based code.

Step 2: The Key Concepts of RxJS

Concept	Description
Observable	An `Observable` is a stream of data that can be subscribed to.
Observer	An `Observer` is an object with `next()`, `error()`, and `complete()` methods that is used to subscribe to an `Observable`.
Operator	An `Operator` is a function that can be used to transform, filter, or combine `Observable`s.
Subscription	A `Subscription` represents the execution of an `Observable`. It can be used to unsubscribe from an `Observable`.

Step 3: How RxJS is Used in Angular

RxJS is used extensively in Angular for a variety of tasks, such as:

HTTP requests: The HttpClient in Angular returns an Observable that can be used to handle the response from an HTTP request.
Forms: The FormControl in Angular has a valueChanges property that is an Observable that can be used to listen for changes to the value of a form control.
Routing: The Router in Angular has an events property that is an Observable that can be used to listen for routing events.

Step 4: Solve the Problem

Here’s how we can use RxJS to handle the stream of real-time data from the WebSocket:

import { webSocket } from 'rxjs/webSocket';

const subject = webSocket('ws://localhost:8081');

subject.subscribe(
  (msg) => console.log('message received: ' + msg),
  (err) => console.log(err),
  () => console.log('complete')
);

subject.next(JSON.stringify({ op: 'hello' }));

In this example, we use the webSocket function from RxJS to create an Observable that represents the WebSocket connection. We then subscribe to the Observable to receive the data as it comes in.

Systematic, production-ready debugging

Practice Question

You want to make two HTTP requests in parallel and then do something with the results of both requests. Which of the following would you use?

Questions