Question

39

Reliably detect if the script is executing in a web worker

rated 0 times [ 46] [ 7] / answers: 1 / hits: 18262 / 13 Years ago, fri, october 28, 2011, 12:00:00

I am currently writing a little library in JavaScript to help me delegate to a web-worker some heavy computation .

For some reasons (mainly for the ability to debug in the UI thread and then run the same code in a worker) I'd like to detect if the script is currently running in a worker or in the UI thread.

I'm not a seasoned JavaScript developper and I would like to ensure that the following function will reliably detect if I'm in a worker or not :

function testenv() {

    try{

        if (importScripts) {

            postMessage(I think I'm in a worker actually.);

        }

    } catch (e) {

        if (e instanceof ReferenceError) {

            console.log(I'm the UI thread.);

        } else {

            throw e;

        }

    }

}

So, does it ?

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marinal

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2 Years ago

answered 13 Years ago ravenl · Accepted Answer

As noted there is an answer in another thread which says to check for the presence of a document object on the window. I wanted to however make a modification to your code to avoid doing a try/catch block which slows execution of JS in Chrome and likely in other browsers as well.

EDIT: I made an error previously in assuming there was a window object in the global scope. I usually add

//This is likely SharedWorkerContext or DedicatedWorkerContext

window=this;

to the top of my worker loader script this allows all functions that use window feature detection to not blow up. Then you may use the function below.

function testEnv() {

  if (window.document === undefined) {

    postMessage(I'm fairly confident I'm a webworker);

  } else {

    console.log(I'm fairly confident I'm in the renderer thread);

  }

}

Alternatively without the window assignment as long as its at top level scope.

var self = this;

function() {

  if(self.document === undefined) {

    postMessage(I'm fairly confident I'm a webworker);

  } else {

    console.log(I'm fairly confident I'm in the renderer thread);

  }

}