How do I prevent the slow script warning and force the browser to continue running script until it's finished?

Question

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UPDATE (5 July 2013):

I've learned much since I originally asked this question. In one of the comments below it was suggested that I re-approach the task and find a way to solve it without risk of blocking the UI. I said it was impossible, the function must run as is. I don't actually remember what I was trying to accomplish with the function, but I'm certain that the commenter was right, and I was wrong. If you stumble upon this question and are in a similar situation as I was, then consider very seriously the possibility that your approach is flawed.

You might also want to look into web workers.

Here is where you can expect them to work.

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Original Question:

Rather than get overly specific to my problem, I'll keep this generic so other people who stumble upon this can find it useful.

I have a function that accepts one parameter, a string. If the string is short the function runs fine and completes in a timely fashion. If, however, the string that's passed in is too long the script runs for a bit, then eventually times out and returns the browser's slow script dialog that allows the user to kill the script.

I would like to prevent that from happening so the script can continue to its terminus.

How can this be done?

A side note: If I can get this working, I would also like to make a status bar, similar to the one you see when loading gmail, appear so the user knows things are happening.

Thanks!

Answer 1

You can try not blocking the UI completely and make it run "in another thread" with setTimeout.

window.setTimeout(function() { ... code ... }, 0);

I say "in another thread" because there is no real multi-thread in JS, and here is an nice article about it

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EDIT: (To make this answer more up-to-date with web technologies)

You can also use HTML 5 Web Workers depending on the browser you are targeting

Answer 2

No way you can disable that behavior in any browser by script. Imagine the impact, disable that feature and call a while(1). Pretty bad.

It's on you to create code which does not block the browser for "too long". There are a ton if best-practice patterns. I always recommend to try to break down your algorythm into smaller chunks. Combine that with a runaway-timer and a loop which makes sure that any operation does not run for longer than 100ms (for instance).

var sequence = ['foo', 'bar', 'baz', 'base', 'ball', 'hello', 'world', '100k more'],
    start = Date.now();

setTimeout(function _worker() {
    do {
       var element = sequence.shift();
       // do something with element
    } while( sequence.length && (Date.now() - start < 100) );

    if( sequence.length )
        setTimeout(_worker, 25);
}, 25);