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I'm going thru some legacy code and I've noticed the following line(s):

// Stray timeout
var t = setTimeout('',1);

Does it do anything? Is it really required?

There is a following question on SO: Why is setTimeout(fn, 0) sometimes useful?

The solution is to "pause" the JavaScript execution to let the rendering threads catch up. And this is the effect that setTimeout() with a timeout of 0 does. It is like a thread/process yield in C. Although it seems to say "run this immediately" it actually gives the browser a chance to finish doing some none-JavaScript things that have been waiting to finish before attending to this new piece of JavaScript.

That explains benefits of executing a function in setTimeout. But how about executing an empty string?

Community
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Mars Robertson
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2 Answers2

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setTimeout('',1)

This line does absolutely nothing. You are telling JavaScript to eval() the string ''. That does nothing.

Sometimes doing this is useful, as it "pushes the code to the bottom of the stack" to run it after the function (and whatever UI updates the browser is doing) finishes.

For example:

setTimeout(function(){
    // Work with some DOM elements, after the browser has a second to render them
}, 0);

But I can't see an empty string having any effect on anything.

EDIT: In Google Chrome, if you do setTimeout('',1) it doesn't return you anything. Normally, it would return you the timeout_id, so you could cancel it with clearTimeout. But, in Google Chrome, setTimeout('',1) returns undefined, which makes be believe it doesn't even set a timeout, since you didn't give it anything to do. So, yeah, it literally does absolutely nothing.

gen_Eric
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    Why a down-vote? Am I wrong? Does `setTimeout('',1)` (or `eval('')`) actually do anything? I can't think of this actually having any effect (good or bad) on anything. – gen_Eric May 12 '14 at 18:38
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    I have no idea why someone down voted this. It's a perfectly correct answer. – Jimmy Breck-McKye May 12 '14 at 18:39
2

One possibility is that it is a browser version test.

For example, in IE9,

setTimeout('',1)

returns undefined. However in IE10, it returns an integer. As Rocket Hazmat pointed out, which I also confirmed, Chrome 33 returns undefined.

Matt
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  • This is possible, but what exactly is it testing for? You got `undefined`... now what? Is it Chrome? IE9? This is a good theory, though it's a bad way to implement a browser check. +1 though for the theory. – gen_Eric May 12 '14 at 19:29
  • Agreed, this would be quite an incomplete test if this were it. That's why I upvoted Bergi's question about how `t` is used. – Matt May 12 '14 at 19:47