Why does not Chrome allow Web Workers to be run in JavaScript?

Question

If I try to use web workers through a JavaScript file, Chrome throws an error -

Uncaught SecurityError: Failed to create a worker: script at '(path)/worker.js' cannot be accessed from origin 'null'.

But it allows them if we use directly through the HTML.

The answer on Chrome can't load web worker says Chrome doesn't let you load web workers when running scripts from a local file.

Why doesn't chrome allow web workers to run locally?

Web Workers work completely fine in Firefox, Safari and in Edge

Solution 1

This question was already asked. The workers should work in HTML files opened from disk as long as you use relative path. However, if chrome implements this correctly has been disputed.

I advise that you try to use relative path in your scripts:

new Worker("./scripts/worker.js");

If that doesn't work, see this workaround: https://stackoverflow.com/a/33432215/607407

Specifically, load worker as a function, then convert the function to string:

function worker_function() {
    // all worker code here
}
var worker = new Worker(URL.createObjectURL(new Blob(["("+worker_function.toString()+")()"], {type: 'text/javascript'})));

Solution 2

var cblock=`

function workerFunc(e){

    console.info('Hello World!',e.data.msg)
    postMessage({msg:'Complete!'})
}

addEventListener('message',workerFunc)
`    
var a=new Worker(URL.createObjectURL(new Blob( [cblock], {type:'text/javascript'} )))    
a.onmessage=function(e){ console.info('My worker called!',e.data.msg) }    
a.onerror=function(e){ console.info( JSON.stringify(e,' ',2) ) }    
a.postMessage({ msg:'Chrome WebWorkers work!' }) 

// Hello World! Chrome WebWorkers work!
// My worker called! Complete! 

Comments

[Jim]

web workers have been supported by chrome since version 4.00, perhaps share your code? I suspect it's access to worker.js that's the problem.

[Morten Olsen]

Are your application running http (http://, https://) or streight from the file system (file://)?

[Inderpartap Cheema]

The answer you mentioned says "Chrome doesn't let you load web workers when running scripts from a local file." This was my actual question. Why can't we use workers locally in Chrome?

[utdev]

if the worker js file is in the same dir I just need to call it like this correct? new Worker("worker.js");

[Tomáš Zato]

@InderpartapCheema If you're asking Why, then it's off topic, see help center.

[Vasily Hall]

It's on topic and I also am curious about this + the more questions the merrier- I for one am googling this in 2018 and am frustrated by the sheer absence of identical such questions as by now I expect there to be dozens of answers for this kind of thing , each shining their own hint of wisdom on the subject.

[Tomáš Zato]

@VasilyHall I understand your curiosity and frustration. But asking "why" did Google Chrome team make decision about a feature is not on topic on stackoverflow: It would be pure speculation - unless one of the decision makers actually weighs in.

[Vasily Hall]

Fair enough, maybe in years ahead some engineers would pop on this thread and anonymously spill the secret.

[Vasily Hall]

On another note, I'm excited to try your solution from another post - about doing a quick internally-external script via Blob object!

[agiopnl]

The relative URL didn't work in any of my browsers, but the Blob-way worked.