JavaScript and Threads

Question

Is there some way to do multi-threading in JavaScript?

Answer 1

Javascript doesn't have threads, but we do have workers.

Workers may be a good choice if you don't need shared objects.

Most browser implementations will actually spread workers across all cores allowing you to utilize all cores. You can see a demo of this here.

I have developed a library called task.js that makes this very easy to do.

task.js Simplified interface for getting CPU intensive code to run on all cores (node.js, and web)

A example would be

function blocking (exampleArgument) {
    // block thread
}

// turn blocking pure function into a worker task
const blockingAsync = task.wrap(blocking);

// run task on a autoscaling worker pool
blockingAsync('exampleArgumentValue').then(result => {
    // do something with result
});

Answer 2

In raw Javascript, the best that you can do is using the few asynchronous calls (xmlhttprequest), but that's not really threading and very limited. Google Gears adds a number of APIs to the browser, some of which can be used for threading support.

Answer 3

See http://caniuse.com/#search=worker for the most up-to-date support info.

The following was the state of support circa 2009.

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The words you want to google for are JavaScript Worker Threads

Apart from from Gears there's nothing available right now, but there's plenty of talk about how to implement this so I guess watch this question as the answer will no doubt change in future.

Here's the relevant documentation for Gears: WorkerPool API

WHATWG has a Draft Recommendation for worker threads: Web Workers

And there's also Mozilla’s DOM Worker Threads

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Update: June 2009, current state of browser support for JavaScript threads

Firefox 3.5 has web workers. Some demos of web workers, if you want to see them in action:

• Simulated Annealing ("Try it" link)
• Space Invaders (link at end of post)
• MoonBat JavaScript Benchmark (first link)

The Gears plugin can also be installed in Firefox.

Safari 4, and the WebKit nightlies have worker threads:

• JavaScript Ray Tracer

Chrome has Gears baked in, so it can do threads, although it requires a confirmation prompt from the user (and it uses a different API to web workers, although it will work in any browser with the Gears plugin installed):

• Google Gears WorkerPool Demo (not a good example as it runs too fast to test in Chrome and Firefox, although IE runs it slow enough to see it blocking interaction)

IE8 and IE9 can only do threads with the Gears plugin installed

Answer 4

If you can't or don't want to use any AJAX stuff, use an iframe or ten! ;) You can have processes running in iframes in parallel with the master page without worrying about cross browser comparable issues or syntax issues with dot net AJAX etc, and you can call the master page's JavaScript (including the JavaScript that it has imported) from an iframe.

E.g, in a parent iframe, to call egFunction() in the parent document once the iframe content has loaded (that's the asynchronous part)

parent.egFunction();

Dynamically generate the iframes too so the main html code is free from them if you want.

Answer 5

With the HTML5 "side-specs" no need to hack javascript anymore with setTimeout(), setInterval(), etc.

HTML5 & Friends introduces the javascript Web Workers specification. It is an API for running scripts asynchronously and independently.

Links to the specification and a tutorial.

Answer 6

You could use Narrative JavaScript, a compiler that will transforms your code into a state machine, effectively allowing you to emulate threading. It does so by adding a "yielding" operator (notated as '->') to the language that allows you to write asynchronous code in a single, linear code block.