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A WebWorker executes with a scope completely separate from the 'window' context of traditional JavaScript. Is there a standard way for a script to determine if it is, itself, being executed as a WebWorker?
The first 'hack' I can think of would be to detect if there is a 'window' property in the scope of the worker. If absent, this might mean we are executing as a WebWorker.
Additional options would be to detect properties not present in a standard 'window' context. For Chrome 14, this list currently includes:
FileReaderSync
FileException
WorkerLocation
importScripts
openDatabaseSync
webkitRequestFileSystemSync
webkitResolveLocalFileSystemSyncURL
Detecting WorkerLocation seems like a viable candidate, but this still feels a bit hackish. Is there a better way?
EDIT: Here is the JSFiddle I used to determine properties present in the executing WebWorker that are now in 'window'.
882
You need to use the postMessage() method in the onmessage event handler in worker. js : // src/worker. js onmessage = e => { const message = e.
A web worker is a JavaScript running in the background, without affecting the performance of the page.
We use them in the following way: we check for the availability of the Worker() constructor in the browser, and if it is available, we instantiate a worker object, with the script URL as the argument. This script will be executed on a separate thread.
importScripts() tells your main service worker script to pause its current execution, download additional code from a given URL, and run it to completion in the current global scope. Once that's done, the main service worker script resumes execution.
The spec says:
The DOM APIs (Node objects, Document objects, etc) are not available to workers in this version of this specification.
This suggests checking for the absence of document is a good way to check you're in a worker. Alternatively you could try checking for the presence of WorkerGlobalScope?
195
Although post a bit old, adding a couple of generic alternatives What is used in Asynchronous.js library (a library for generic handling of asynchronous/parallel processes, author) is the following:
// other declarations here
,isNode = ("undefined" !== typeof global) && ('[object global]' === Object.prototype.toString.call(global))
// http://nodejs.org/docs/latest/api/all.html#all_cluster
,isNodeProcess = isNode && !!process.env.NODE_UNIQUE_ID
,isWebWorker = !isNode && ('undefined' !== typeof WorkerGlobalScope) && ("function" === typeof importScripts) && (navigator instanceof WorkerNavigator)
,isBrowser = !isNode && !isWebWorker && ("undefined" !== typeof navigator) && ("undefined" !== typeof document)
,isBrowserWindow = isBrowser && !!window.opener
,isAMD = "function" === typeof( define ) && define.amd
,supportsMultiThread = isNode || "function" === typeof Worker
,isThread = isNodeProcess || isWebWorker
// rest declarations here..
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