INTRODUCTION TO WORKERS

A single JavaScript environment is essentially a virtualized environment running inside the host operating system. Each open page in a browser is allocated its own environment. This provides each page its own memory, event loop, DOM, and so on. Each page is more or less sandboxed and cannot interfere with other pages. It is trivial for a browser to manage many environments at once—all of which are executing in parallel.

Using workers, browsers are able to allocate a second child environment that is totally separated from the original page environment. This child environment is prevented from interacting with single-thread–dependent constructs such as the DOM, but is otherwise free to execute code in parallel with the parent environment.

Comparing Workers and Threads

Introductory resources will commonly draw a comparison between workers and execution threads. In many ways, this is an apt comparison, as workers and threads do indeed share many characteristics...