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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
Network Information API	provides information about the system's connection in terms of general connection type (e.g., 'wifi', 'cellular', etc.).	53.0 (53) only on mobile	(Yes) only on mobile	No support	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)
Server-sent events	Allows a server to push data to a web page at any point, after a connection has been opened to it.	53 (53) (currently only available in dedicated and shared workers; not service workers.)	?	(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)

Web Workers API: Functions and classes available to workers

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

APIs available in workers

See also