dom events - Killing a JavaScript function which runs infinite - Stack Overflow

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As an example

var runInfinite = function(){
    while(1)
    {
       // Do stuff;
    }
};

setTimeout(runInfinite, 0);

Is it possible to break this runInfinite function form running infinite? I mean is it possible to kill this function from another function without using a flag or return statement?

As an example

var runInfinite = function(){
    while(1)
    {
       // Do stuff;
    }
};

setTimeout(runInfinite, 0);

Is it possible to break this runInfinite function form running infinite? I mean is it possible to kill this function from another function without using a flag or return statement?

• javascript
• dom-events

Share Improve this question Follow edited Aug 19, 2019 at 11:21 Brian Tompsett - 汤莱恩 5,8937272 gold badges6161 silver badges133133 bronze badges asked Feb 14, 2013 at 8:28 SomnathSomnath 3,27544 gold badges3030 silver badges4343 bronze badges 7

• 1 Why do you rule out using a flag? Seems like the perfect place to use one. – nunespascal Commented Feb 14, 2013 at 8:30
• 2 AFAIK, the while(1) block will literally block the thread and not allow anything else to run. I don't have sources other than experience. (or maybe it just gets so slow that it es to an effective freeze) If I had documentation, I'd post as an answer. – AI Generated Response Commented Feb 14, 2013 at 8:30
• 1 JavaScript (in browsers) is single threaded so the while loop actually blocks the thread; and you have no other thread which you could use to poll/set the flag. – Salman Arshad Commented Feb 14, 2013 at 8:34
• @nunespascal lets think i have a stack of functions provided by users. I run them one after another. The problem is i can not ask users to put a flag inside their function. That's why I ruled out using a flag from my question. – Somnath Commented Feb 14, 2013 at 8:36
• 1 @Somnath Sorry, mate, but in that case you are doomed. :) But seriously, you should not allow that. Scripts provided by users is a serious security issue. – freakish Commented Feb 14, 2013 at 8:37

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6 Answers 6

Sorted by: Reset to default 5

The answer is no. Since JavaScript is single-threaded ( unless you are using some less mon implementation which I doubt ) nothing can break a loop ( or any other block of code ) from outside.

There is no direct way to "kill" a running javascript function.

Possible workaround, although you need to replace the while(1) loop:

var i = 0; // for testing purposes

var toCall = "runInfinite()";
function runInfinite(){
    // do stuff
    console.log(i++);
    setTimeout(function(){ eval(toCall); }, 100); // or whatever timeout you want
}

setTimeout(function(){ eval(toCall); }, 0); // start the function
setTimeout(function(){ toCall = ""; }, 5000); // "kill" the function

I know using eval() is considered to be bad practice, however the idea should be clear. The function calls itself (not recursive, therefore the setTimeout()) using the toCall variable. Once this variable is unset, you kill it from outside.

You could wrap these variables and functions in a class so you can implement your "kill" function.

I've just tested on my browser.

AFAIK, the while(1) block will literally block the thread and not allow anything else to run. I don't have sources other than experience, but using the Chrome developer toolkit thing ctrl+shift+i typing while(1){} will block everything else due to the fact that browser-javascript is single threaded.

However, if you're using node.js, you may be able to as it has multithreading capabilities. If anyone is familiar enough with node.js and is willing to answer/edit, go for it. I've never quite used it.

The whay you want not really. But maybe you're doing it wrong. Try not to use while(1) if possible and at the end of the function call the function again if the outside flag triggered but some break button is not set, or return if otherwise

I admit this is not exactly the same, but, there are the Javascript generators and Javascript iterators in ECMA-262. If you can replace your function with a generator function, then, you can implement the breakable feature easily.

function execWithTimeout(iter, timeout = 100) {
    const limit = Date.now() + timeout
    for (const output of iter) {
        console.log(output)
        if (Date.now() > limit) throw(new Error("Timeout reached"))
    }
}

let runInfinite = function * () {
    let i = 0
    while (1) {
        yield i++
    }
}

execWithTimeout(runInfinite())

return can be used to stop a function from its current execution but not in your case.

In your case you could try to your function are wrapped in a try / catch block, you can find it out when your function gonna infinite ,based on that you can terminate its current execution.

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