Web Workers API: Functions and classes available to 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.

Workers run in another global context, DedicatedWorkerGlobalScope different from the current window. By default methods and properties of Window are not available to them, but DedicatedWorkerGlobalScope, like Window, implements WindowTimers and WindowBase64.

Comparison of the properties and methods of the different type of workers

Function	Dedicated workers	Shared workers	Service workers	Chrome workers	Outside workers
atob()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on Window
btoa()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on Window
clearInterval()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on Window
clearTimeout()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on Window
dump()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on Window
setInterval()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on Window
setTimeout()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on Window
importScripts()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	no
close()	yes, on WorkerGlobalScope	yes, on WorkerGlobalScope	yes, but is a no-op.	Unknown	no
postMessage()	yes, on DedicatedWorkerGlobalScope	no	no	Unknown	no

APIs available in workers

Function	Functionality	Support in Gecko (Firefox)	Support in IE	Support in Blink (Chrome and Opera)	Support in WebKit (Safari)
Broadcast Channel API	Allows simple communication between browsing contexts (that is windows, tabs, frames, or iframes) with the same origin (usually pages from the same site).	38 (38)	No support	No support	No support
Cache	Cache API provides the ability to programmatically control cache storage associated with current origin.	(Yes)	No support	43	?
Channel Messaging API	Allows two separate scripts running in different browsing contexts attached to the same document (e.g., two IFrames, or the main document and an IFrame, two documents via a SharedWorker, or two workers) to communicate directly via two ports.	41 (41)	(Yes)	(Yes)	(Yes)
Console API	Provides access to the browser's debugging console (e.g., the Web Console in Firefox). The specifics of how it works vary from browser to browser, but there is a de facto set of features that are typically provided.	38 (38)	(Yes)	(Yes)	(Yes)
CustomEvent	The CustomEvent interface represents events initialized by an application for any purpose.	48 (48)	(Yes)	(Yes)	(Yes)
Data Store	A powerful, flexible storage mechanism for multiple Firefox OS applications to use to store and share data between one another quickly, efficiently, and securely.	Only in Firefox OS internal (certified) applications, since v1.0.1.	No support	No support	No support
DOMRequest and DOMCursor	Respectively, these objects represents an ongoing operation (with listeners for reacting to the operation completely successfully, or failing, for example), and an ongoing operation over a list of results.	41 (41)	?	?	?
Fetch	The Fetch spec provides an up-to-date definition of, and API for, fetching resources (e.g. across the network.)	Mostly in 34 (34) behind pref, although a few features are later.	No support	42 41 behind pref	No support
FileReader	This API allows asynchronous read of Blob and File objects.	46 (46)	No support	(Yes)	No support
FileReaderSync	This API allows synchronous read of Blob and File objects. This is an API that works only in workers.	8 (8)	No support	No support	No support
FormData	FormData objects provide a way to easily construct a set of key/value pairs representing form fields and their values, which can then be easily sent using the XMLHttpRequest send() method.	? (should be in 39 (39))	?	(Yes)	?
ImageData	The underlying pixel data of an area of a canvas element. Manipulating such data can be a complex task better suited to be delegated to a Web Worker.	25 (25)	No support	No support	No support
IndexedDB	Database to store records holding simple values and hierarchical objects.	37 (37), 42 (42) for IDBCursorWithValue.	10.0	(Yes)	No support
Notifications	Allows web pages to control the display of system notifications to the end user	41 (41)	?	?	?
Performance	The Performance interface represents timing-related performance information for the given page.	34.0 (34.0)	?	33.0	?
Promise	JavaScript objects that allow you to write asynchronous functions.	28 (28)	(Yes)	(Yes)	(Yes)
ServiceWorkerRegistration	You can register a service worker from inside a standard worker, and use associated functionality.	40 (40)	No support	(Yes)	No support
TextEncoder and TextDecoder	Create and return a new TextEncoder, or respectively TextDecoder, allowing to encode or decode strings into specific encodings.	20 (20)	No support	No support	No support
URL	Workers can use the static methods URL.createObjectURL and URL.revokeObjectURL with Blob objects accesible to the worker. Workers can also create a new URL using the URL() constructor and call any normal method on the returned object.	21 (21) and 26 (26) for URL() constructor	No support	No support	No support
WebGL with OffscreenCanvas	WebGL (Web Graphics Library) is a JavaScript API for rendering interactive 3D and 2D graphics within any compatible web browser without the use of plug-ins.	44 (44) behind a feature preference setting. In about:config, set gfx.offscreencanvas.enabled to true.	No support	No support	No support
WebSocket	Creates and returns a new WebSocket object; this mimics the behavior of the standard WebSocket() constructor.	37 (37)	11.0	(Yes)	(Yes)
Worker	Creates a new Worker. Yes, workers can spawn more workers.	3.5 (1.9.1)	10.0	No support See crbug.com/31666	No support
WorkerGlobalScope	The global scope of workers. This objects defines worker-specific functions.	(Yes)	10.0	(Yes)	(Yes)
WorkerLocation	The subset of the Location interface available to workers.	3.6 (1.9.2)	10.0	(Yes)	(Yes)
WorkerNavigator	The subset of the Navigator interface available to workers.	Basic implementation (Yes) appCodeName, product, taintEnabled(): 28 (28) onLine: 29 (29) NavigatorLanguage: (Yes)	appName, appVersion, onLine, platform, userAgent: 10.0 Other: No support	(Yes)	(Yes)
XMLHttpRequest	Creates and returns a new XMLHttpRequest object; this mimics the behavior of the standard XMLHttpRequest() constructor. Note that the responseXML and channel attributes on XMLHttpRequest always return null.	Basic: 3.5 (1.9.1) response and responseType are available since 10 (10) timeout and ontimeout are available since 13 (13)	(Yes)	(Yes)	(Yes)

See also

• Using web workers
• Worker