Understanding Multi-threaded Applications in jQuery

As the demand for more efficient and responsive web applications continues to grow, understanding the concept of multi-threading becomes increasingly crucial. In JavaScript, this concept is introduced through the use of Web Workers. However, when using jQuery, a popular JavaScript library designed to simplify HTML document traversing, event handling, and animation, multi-threading needs to be approached from a slightly different angle. This article seeks to deepen the understanding of multi-threading in the context of jQuery, using references from the comprehensive JavaScript article, “Understanding Multi-threaded Applications in JavaScript“.

Leveraging JavaScript’s Multi-threading in JQuery

jQuery does not natively support multi-threading since it is fundamentally built on JavaScript, which is inherently single-threaded. Nevertheless, by tapping into JavaScript’s underlying capabilities, specifically Web Workers, jQuery can indirectly leverage multi-threading.

A previous article provides a detailed explanation of JavaScript’s approach to multi-threading through Web Workers. It outlines how Web Workers run scripts in the background separate from the main execution thread, preventing blocking and enhancing performance.

Given jQuery’s reliance on JavaScript, creating a Web Worker in jQuery follows the same process:

let worker = new Worker('worker.js');

Communication between the jQuery script (main thread) and the worker thread, as well as use-cases and benefits, also remain consistent with the JavaScript approach as detailed in the referenced article.

jQuery Deferred and Promise: Simulating Multi-threading

Despite the utility of Web Workers, it’s important to note that they don’t fit all use cases, particularly those that manipulate the Document Object Model (DOM). This limitation stems from the fact that Web Workers run in a separate context and don’t have access to the DOM.

For situations where DOM manipulation is needed, jQuery offers two tools that can simulate multi-threaded behavior: Deferred and Promise objects. While not truly multi-threading, these tools offer a way to manage asynchronous operations, thereby enhancing responsiveness and efficiency.

The Deferred object in jQuery is a constructor function that creates deferred objects. These objects represent a unit of work that has not yet been completed. Deferred objects have methods like .done(), .fail(), and .always() that are called when the Deferred is resolved, rejected, or either completed, respectively.

A Promise, on the other hand, is an object that represents a placeholder for the eventual results of a deferred object. Promises allow you to organize asynchronous jQuery operations and specify callbacks to handle the results without blocking the main thread.

Below is an example of how Deferred and Promise are used in jQuery:

$.get("example.php") // Returns a Promise object
    .done(function() {
    .fail(function() {
    .always(function() {

This example fetches data from ‘example.php’. The .get() method returns a Promise, and the .done(), .fail(), and .always() methods are used to attach callback functions that will run when the request is completed.


Although jQuery does not natively support multi-threading, it offers tools and leverages JavaScript’s capabilities to manage multiple operations simultaneously. This enhances responsiveness and efficiency, particularly for web applications that require heavy computations, data fetching and processing, and real-time interactions.

Web Workers offer a direct approach to multi-threading in jQuery, allowing for concurrent operations separate from the main execution thread. In cases where DOM manipulation is necessary, jQuery’s Deferred and Promise objects provide a way to manage asynchronous operations effectively. Understanding when and how to use these tools is fundamental for developing efficient, responsive jQuery applications.

Leave a Reply