Before you can create a worker, you need a JavaScript file with code that runs in the worker thread. You can see a simple example of a worker definition file at https://github.com/mdn/simple-web-worker/blob/gh-pages/worker.js. The file should contain a message event listener that performs operations when messages are received from other threads and responds accordingly.

Once that file is created, you're ready to use it with a worker. A worker is created by passing a URL argument to the Worker() constructor. The URL can be a string representing the name of the file with your worker definition code, or constructed using a Blob. The Blob technique can be useful if you're fetching the worker definition code from a server. The example application demonstrates how to use both approaches. Let's move on to the process of integrating WebAssembly with Web Workers.