Functions and classes available to Web Workers

In addition to the standard JavaScript set of functions (such as String, Array, Object, JSON, etc.), there are a variety of functions available from the DOM to workers. This article provides a list of those.

Worker Contexts & Functions

Workers run in a different global context than the current window! While Window is not directly available to workers, many of the same methods are defined in a shared mixin (WindowOrWorkerGlobalScope), and made available to workers through their own WorkerGlobalScope-derived contexts:

DedicatedWorkerGlobalScope for dedicated workers
SharedWorkerGlobalScope for shared workers
ServiceWorkerGlobalScope for service workers

Some of the functions (a subset) that are common to all workers and to the main thread (from WindowOrWorkerGlobalScope) are:

atob()
btoa()
clearInterval()
clearTimeout()
createImageBitmap()
dump() Non-standard
fetch()
queueMicrotask()
reportError()
setInterval()
setTimeout()
structuredClone()
requestAnimationFrame() (dedicated workers only)
cancelAnimationFrame() (dedicated workers only)

The following functions are only available to workers:

WorkerGlobalScope.importScripts() (all workers)
DedicatedWorkerGlobalScope.postMessage() (dedicated workers only)

Web APIs available in workers

Note: If a listed API is supported by a platform in a particular version, then it can generally be assumed to be available in web workers. You can also test support for a particular object/function using the site: https://worker-playground.glitch.me/

The following Web APIs are available to workers:

Workers can also spawn other workers, so these APIs are also available:

Worker Contexts & Functions

Web APIs available in workers

See also