Does the browser keep track of active timer IDs?

StackOverflow https://stackoverflow.com/questions/2814919

Question

Does the browser keep track of active setInterval and setTimeout IDs? Or is this solely up to the developer to keep track of?

If it does keep track of them, is it accessible via the BOM?

Was it helpful?

Solution

It is up for the developer to keep track of. You can do so by using the returned value of the setTimeout/setInterval function and passing that value to the clearTimeout/clearInterval function - as described in other answers here.

This appears to be because each browser will implement keeping track of the intervals in their own way.

From w3.org/TR/2009/WD-html5-20090212/no.html (a draft, but w3schools and http://w3.org/TR/Window explain it almost the same way) - setTimeout and setInterval return a long and clearTimeout/clearInterval accept a long to find and cancel

OTHER TIPS

You can add such global timers tracking by overriding the setTimeout/seInterval functions. As a bonus you easily add code when a timer is set or popped, track live timers or popped timers, etc...

For example:

timers = {}; // pending timers will be in this variable
originalSetTimeout = window.setTimeout;
// override `setTimeout` with a function that keeps track of all timers
window.setTimeout = function(fu, t) {
    var id = originalSetTimeout(function() {
        console.log(id+" has timed out");
        delete timers[id]; // do not track popped timers 
        fu();
    }, t);
    // track this timer in the `timers` variable
    timers[id] = {id:id,  setAt: new Date(),  timeout: t};
    console.log(id+" has been set to pop in "+t+"ms");
}
// from this point onward all uses of setTimeout will be tracked, logged to console and pending timers will be kept in the global variable "timers".

This may interest you, if you are curious about how the timer is 'remembered' by its window.

<!doctype html> 
<html lang= "en"> 
<head> 
<meta charset= "utf-8"> 
<title>Timer </title> 
</head> 
<body>
<h1>Timers</h1>
<script>

if(!window.timers){
    var timers= [], i= 0;
    while(i<5){
        timers.push(setInterval(function(){
            if(confirm(timers.join('\n')+'\nRemove a timer?')){
                clearInterval(timers.shift());
            }
        },
        i*1000+1000));
        ++i;
    }
}
</script>

</body> 
</html>

Update:

There are 2 aspects to this question.

  1. Does the browser keep track of timer IDs?
  2. Are they accessible

I can only presume for #1 (and later #2) that the OP means "are they tracked" in the general sense because as a Developer s/he would like control over them.

In short, yes they are tracked (as @s_hewitt noted, as long values by the browser) and they can be managed by the developer by maintaining a reference to the timers when setup.

As a developer you can control (e.g. stop) them by calling (clearInterval(handleRef), or clearTimeout(handleRef))

However there is no default window.timers or similar collection that gives you a list of the existing timers - you will need to maintain that yourself if you feel you need to.

function startPolling(delay){
  pollHandle = setInterval(doThis, delay);
}
function stopPolling(){
  clearInterval(pollHandle);
}

function doThisIn30minUnlessStopped(){
  timerHandle = setTimeout(doThisThing, 1800000);
}
function stop30minTimer(){
  clearTimeout(timerHandle);
}

You simply need to create a variable reference to your timer, and if/when needed, clear it by name.

When you load another page, all the timers are automatically cleared by the browser so you don't need to maintain a handle, and clear them unless you need/want to.

Look at the scripts below, the browser could remember the id of each setTimeout iteration

for (i = 1; i <= d; i++) {
          (function(j) {
                var delay = j/d; 
               t[j] = setTimeout(function() {      
                      elem.style.top = j+"px";
                     },delay);

            })(i);           
 }

You can access them by

for (i in t) {
      alert(t[i]);  
 }
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