Worklets are a relatively new concept in web development that allow developers to run JavaScript code in a separate thread, providing a way to perform CPU-intensive tasks without blocking the main thread of the browser. In this blog, we'll explore what worklets are, how they work, and provide an example of how to use them in your web development projects.

What is a Worklet?

A worklet is a JavaScript module that runs on a separate thread in the browser. Unlike regular JavaScript code, which runs on the main thread, worklets are designed to perform specific tasks that require a lot of processing power, without affecting the performance of the main thread. Worklets are part of the larger "Houdini" project, which aims to provide developers with more control over the rendering process of their web applications.

How do Worklets Work?

When a worklet is created, it runs in a separate thread from the main thread of the browser. This means that it can perform CPU-intensive tasks without blocking the main thread. The main thread can then continue to handle user input and render the page, while the worklet runs in the background.

There are several types of worklets, each with their own specific use case:

1. Paint Worklets: These worklets allow developers to define custom paint behavior for elements on a web page. This can include custom backgrounds, borders, and even animations.

2. Layout Worklets: These worklets allow developers to define custom layout behavior for elements on a web page. This can include custom sizing and positioning of elements.

3. Animation Worklets: These worklets allow developers to define custom animation behavior for elements on a web page. This can include custom timing and easing functions.

Example of Using a Paint Worklet:

To help illustrate how worklets work, let's take a look at an example of using a paint worklet to create a custom background for an element on a web page.

First, we'll create a new JavaScript file called "my-paint-worklet.js". In this file, we'll define our custom paint behavior for the element:

In this code, we're defining a new class called "MyPaintWorklet" that extends the built-in "PaintWorklet" class. We're also defining a static "inputProperties" method that returns an array of CSS property names that the worklet will use as input.

Finally, we define the "paint" method, which takes a canvas context, a geometry object, and a set of properties as input. In this method, we're getting the value of the "--my-color" CSS property from the properties object, setting the fill style of the canvas context to that color, and filling a rectangle with that color.

Once we've defined our worklet, we can use it in our CSS code by setting the "--my-color" property and using the "paint()" function with the "my-paint-worklet" identifier:

In this code, we're setting the "--my-color" property to "#ff0000", which will set the background color of the element to red. We're also using the "paint()" function with the "my-paint-worklet" identifier, which will apply our custom paint behavior to the element.