Does the browser keep track of active timer IDs?

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?

Answer 1

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

Answer 2

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".