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Web workers in React

Suman Kumar 46

Web workers in React

Suman Kumar
Level Up Coding
Published in
3 min read22 hours ago


Have you ever faced a situation in which you are executing a block of code and it is freezing the UI for a few seconds? If yes then you surely need a solution to handle that block of code in the background.

In React we have a simple way to do these types of CPU-intensive processes in the background with the help of web workers. First of all what a web worker is?

A web worker is a JavaScript feature that allows you to run scripts in the background, separate from the main thread of your web page. This background execution enables you to perform tasks concurrently without blocking the user interface (UI) or causing it to become unresponsive. Web workers are particularly useful for handling computationally intensive or time-consuming operations without impacting the user’s experience.

The use cases for a web worker are

  • Complex Calculations: Web workers are ideal for performing complex mathematical calculations or data processing tasks without impacting the main thread.
  • Large Data Handling: When dealing with large datasets or files, web workers can help process and parse the data in the background.
  • Background Services: Web workers can be used to run background services such as periodic data synchronization or background notifications.

So, let’s try to implement a web worker in a React application.

First, we create a react project, and then we use a service faker to create 25000 user records.

import { faker } from '@faker-js/faker';

export function fetchUsers() {
const users = [];

for (let i = 0; i < 25000; i++) {
let id = i + 1;
let name = faker.person.fullName();
let email = faker.internet.email();
let joinedOn = faker.date.recent();
let commentCount = faker.number.int({ min: 0, max: 100 });
let user = {
return Promise.resolve(users);

Now, our goal is to sort these records ascending and descending based on “commentCount” by using a web worker.

So, first, we will create two files “src/app.worker.js” and “src/WebWorker.js”.

In the “app.worker.js” file we will export an arrow function in which we will add an event listener on the window object(self) to listen to the “message”. This “message” will be triggered from the UI with “users” and “type”(ascending or descending” variables.

export default () => {
self.addEventListener('message', e => { // eslint-disable-line no-restricted-globals
if (!e) return;
let { users, type } = e.data;

if(type === "asc") {
users = users.sort((a, b) => a.commentCount - b.commentCount);
} else {
users = users.sort((a, b) => b.commentCount - a.commentCount);


And we will sort it according to the “type” variable and return it by “postMesssage” method.

And in the “WebWorker.js” we will export a class.

 constructor(worker) {
const code = worker.toString();
const blob = new Blob(['('+code+')()']);
return new Worker(URL.createObjectURL(blob));

It will simply change the worker we defined in “app.worker.js” to an object URL.

Now, let’s connect this webworker to the UI.

First, we will import both the “worker” and “WebWorker” from the respective files.

import worker from './app.worker.js';
import WebWorker from './WebWorker';

Then, we will initialize the “WebWorker” with the argument “worker”.

const webWorker = new WebWorker(worker);

First, we will work on the ascending logic. So, we will send the “users” and “type” to the worker by the “postMessage” method on this web worker.

webWorker.postMessage({ users, type: "asc"});

Then, we will listen to the “message” and get the sorted data from the web worker like this.

webWorker.addEventListener('message', (event) => {
const sortedList = event.data;


Same logic we will add for the descending function as well.

webWorker.postMessage({ users, type: "desc"});
webWorker.addEventListener('message', (event) => {
const sortedList = event.data;


So, now our sorting is working fine. But don't forget to terminate the web worker at the time of component unmounting.

return () => {

So, finally, our application will look something like this.

Working Example- https://6505555525bea36e699fd62c--monumental-cuchufli-bc3416.netlify.app/

Github- https://github.com/sumankalia/react_web_workers/tree/type

If you want to watch this tutorial on YouTube in Hindi. Here’s the link

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Thanks for reading.