JS setTimeout in while loop

Question

Since setTimeout crashes in while loops.

I don't know if there is a way to do it but I am trying to make one. This is how it looks so far.

<script>
var send = true;
function sendit()
{
    alert("test");
    return true;
}
while(true)
{
    if(send == true)
    {
        send = false;
        setTimeout(function(){
            if(sendit() == true) {
                send = true;
            }
        }, 5000);
    }
}
</script>

Is it possible this way?

This is perhaps an XY Problem - what are you trying to solve? Your code here will block as soon as you set send = false as javascript is single threaded, and it's stuck within the while(true) loop at this point, with no chance for the timeout to ever occur. — James Thorpe
– James Thorpe, Commented Sep 4, 2015 at 15:45
possible duplicate of : stackoverflow.com/questions/12996193/… — Anand Dwivedi
– Anand Dwivedi, Commented Sep 4, 2015 at 15:45
@IamkDenok: Quite possibly you are just looking for setInterval() / clearInterval() for what you want to achieve. But it's hard to tell since we don't know what you wanted to achieve in your original code. If the answer linked above (by Anand) does not solve your problem, you might want to ask a different question explaining what you wanted to achieve in the first place. — Ma3x
– Ma3x, Commented Sep 4, 2015 at 15:49
@Ma3x setInterval() is what I was looking for, setInterval() is basically setTimeout in a while loop, thank you! — Iamk Denok
– Iamk Denok, Commented Sep 4, 2015 at 15:55

foz · Accepted Answer · 2015-09-04 15:53:46Z

5

You haven't explained what you want your code to do. If you want it to alert "test" every 5 seconds then you need this:

<script>
function sendit()
{
    alert("test");
    // Call sendit() the next time, repeating
    setTimeout(sendit, 5000);
}
// Call sendit() the first time
setTimeout(sendit, 5000);
</script>

No need for a loop, just get the function to schedule itself again.

answered Sep 4, 2015 at 15:53

foz

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7 Comments

Iamk Denok Over a year ago

This is what I wanted, I also found out that setInterval() archives the effect.

foz Over a year ago

Almost yes. setInterval() will allow sendit() functions to overlap (if they take a long time), whereas the code above will wait for sendit() to finish before waiting another 5 seconds.

Ma3x Over a year ago

It would be better to say, that, since JS is single threaded, using setInterval with a function that takes longer than the specified interval will call the functions one after another right away (possibly freezing the browser). In this case calling setTimeout/setTimeout is better. However, if the function execution time is less than the interval and you need a fixed delay between calls then you should use setInterval.

James Thorpe Over a year ago

@Ma3x Note that there are no guarantees in the spec of a fixed delay between calls. Chances are they will more or less be right, but both setTimeout and setInterval only guarantee a minimum time before firing.

Ma3x Over a year ago

@JamesThorpe: Yes, true. Both are subject to the minimum delay. I meant without the added delay from the function execution, which can add up significantly if the callback takes a few tens of milliseconds to execute.

|

Katana314 · Accepted Answer · 2015-09-04 15:47:15Z

My understanding is that what you're trying to do is the equivalent of Thread.sleep(5000) in a language like Java or C#. That functionality does not exist in JavaScript. If you want to do something some amount of time after your function's execution, put it in a timeout, but one way or another, that first function will still complete in the same frame unless you're performing an enormous amount of work.

Currently, your code is setting a timeout on sendit() a practically-infinite number of times before it returns. Since JavaScript is single threaded, even if 20 seconds passed, it still wouldn't have finished your function and couldn't start looking up timeouts it needs to process. What you should be doing is something like having the inside of the timeout set another timeout, and remove the enclosing while(true). That could allow for infinite, periodic behavior as I think you're looking for.

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