Does the browser keep track of active timer IDs?

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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 t

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情书的邮戳

2021-02-05 09:54

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".

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爱一瞬间的悲伤

2021-02-05 09:54
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.
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生来不讨喜

2021-02-05 09:58

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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不知归路

2021-02-05 10:01

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>

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说谎

2021-02-05 10:07

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

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