why setTimeout is not executed in javascript

Question

I have a function to sleep in javascript like below:

var is_sleep = true;
function sleep(time){
  if (is_sleep){
    is_sleep = false;
    setTimeout("sleep(time)", time);
  }else{
    is_sleep = true;
  }
}
sleep(3000);

However it runs through the statements for is_sleep=true, doesn't run through is_sleep=false statements and doesn't sleep any more.

Could someone tell what the reason is?　Thank you in advance.

icktoofay · Accepted Answer · 2011-02-25 02:57:25Z

6

It's likely that setTimeout is being called, but the string passed to it is failing, as the scope will no longer contain time, which you're referencing. Try replacing that line with this:

setTimeout(function() { sleep(time); }, time);

...which defines a closure, which uses the correct scope. You could also try this:

setTimeout(sleep, time, time);

...which will pass time as an argument to sleep.

answered Feb 25, 2011 at 2:57

icktoofay

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3 Comments

ywenbo Over a year ago

thank you very much. Could you tell me why time in "sleep(time)" is not the time scope? i don't understand it even though it worked, :-)

icktoofay Over a year ago

@ywenbo: Sure. When you pass a string as a parameter to setTimeout, when the timeout goes off, it will eval it in window's scope. time won't be in window's scope; it will be in sleep's now-inaccessible scope. If you use a closure, it inherits the scope from where it's defined. If you use the second method, then it passes sleep as a reference and tells setTimeout to pass time as an argument to it.

ywenbo Over a year ago

very strong and clear explanation, you're nice and great, i very appreciate your help.

Rudu · Accepted Answer · 2011-02-25 02:59:36Z

2

setTimeout runs asynchronously meaning it's not blocking your code execution. Perhaps you knew that, but the function will never live up to the name you chose for it.

First call sleep(3000); calls the sleep function, making the is_sleep variable false, setting a timer, and then immediately returns code execution (to whatever comes after sleep(3000); ;))

If setTimeout was called properly (setTimeout(sleep,time,time);), after 3 seconds, the function would again be called setting is_sleep back to true.

answered Feb 25, 2011 at 2:59

Rudu

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