Viewing all the timeouts/intervals in javascript?

I don't think there is a way to enumerate active timers, but you could override window.setTimeout and window.clearTimeout and replace them with your own implementations which do some tracking and then call the originals.

window.originalSetTimeout = window.setTimeout;
window.originalClearTimeout = window.clearTimeout;
window.activeTimers = 0;

window.setTimeout = function(func, delay) {
    window.activeTimers++;
    return window.originalSetTimeout(func, delay);
};

window.clearTimeout = function(timerID) {
    window.activeTimers--;
    window.originalClearTimeout(timerID);
};

Of course, you might not always call clearTimeout, but this would at least give you some way to track what is happening at runtime.

Seeing as Paul has only covered setTimeout I thought I would share a counter for setInterval/clearInterval.

window.originalSetInterval = window.setInterval;
window.originalClearInterval = window.clearInterval;
window.activeIntervals = 0;
window.setInterval = function (func, delay)
{
    if(func && delay){
            window.activeIntervals++;
    }
    return window.originalSetInterval(func,delay);
};
window.clearInterval = function (intervalId)
{
    // JQuery sometimes hands in true which doesn't count
    if(intervalId !== true){
        window.activeIntervals--;
    }
    return window.originalClearInterval(intervalId);
};

Instead of just have a count of timers, here is an implementation which stores all timerid's into an array. It only shows active timers while the accepted answer only counts calls to setTimeout & clearTimeout.

(function(w) {
    var oldST = w.setTimeout;
    var oldSI = w.setInterval;
    var oldCI = w.clearInterval;
    var timers = [];
    w.timers = timers;
    w.setTimeout = function(fn, delay) {
        var id = oldST(function() {
            fn && fn();
            removeTimer(id);
        }, delay);
        timers.push(id);
        return id;
    };
    w.setInterval = function(fn, delay) {
        var id = oldSI(fn, delay);
        timers.push(id);
        return id;
    };
    w.clearInterval = function(id) {
        oldCI(id);
        removeTimer(id);
    };
    w.clearTimeout = w.clearInterval;

    function removeTimer(id) {
        var index = timers.indexOf(id);
        if (index >= 0)
            timers.splice(index, 1);
    }
}(window));

This is how you can get the count of active timers on the page:

timers.length;

This is how you can remove all active timers:

for(var i = timers.length; i--;)
    clearInterval(timers[i]);

Known limitations:

• You can only pass a function (not a string) to setTimeout with this monkey patch.
• The function assumes clearInterval and clearTimeout do the same, which they do but it could change in the future.

I made a Chrome DevTools extension that shows all intervals. Cleared ones are greyed out.

setInterval-sniffer