We all know that for web applications, perceived performance is highly importance for our users. For data intensive SPAs with CPU-intensive tasks, the single-threaded nature of Javascript starts to hinder the application's perceived performance when you cannot fit those CPU-intensive tasks into a 16.67 ms/frame window (translates to 60fps). That doesn't even account for code execution time of frameworks (React, Vue...etc), which then leaves you with approximately only a 10 ms/frame window or less to complete all your tasks on the main thread to make user interaction feel smooth and snappy.

Mitigate blocking the main thread

Actually, the DOM is not slow. Adding or removing a DOM node is not much more than setting a property on the JS object. However, _layout_ is slow. Imagine adding a DOM node changes the height of the document, it would invoke a bunch of [rendering processes](https://web.dev/rendering-performance/) to redraw the screen. And all the complex algorithms behind the those processes makes any changes in DOM potentially expensive.

Why DOM manipulation is slow?

Modules have always been a part of JavaScript development and providing mechanisms for splitting JavaScript programs up into separate modules that can be imported when needed was the absolutely necessity for JavaScript developers.

JavaScript modules

Parallelism in JavaScript is a technique to improve the performance of web applications by executing multiple tasks simultaneously.

#javascript

J

M

P

W