Question

The window.setTimeout (and related setInterval) function in Javascript allows you to schedule a function to be executed sometime in the future:

id = setTimeout(function, delay);

where “delay” is the number of milliseconds into the future at which you want to have the function called. Before this time elapses, you can cancel the timer using:

clearTimeout(id);

What I want is to update the timer. I want to be able to advance or retard a timer so that the function gets called x milliseconds sooner or later than originally scheduled.

If there were a getTimeout method, you could do something like:

originally_scheduled_time = getTimeout(id);
updateTimeout(id, originally_schedule_time + new_delay);  // change the time

but as far as I can tell there’s nothing like getTimeout or any way to update an existing timer.

Is there a way to access the list of scheduled alarms and modify them?

Is there a better approach?

thanks!

Answer 1

If you really want this sort of functionality, you’re going to need to write it yourself.

You could create a wrapper for the setTimeout call, that will return an object you can use to “postpone” the timer:

function setAdvancedTimer(f, delay) {
  var obj = {
    firetime: delay + (+new Date()), // the extra + turns the date into an int 
    called: false,
    canceled: false,
    callback: f
  }; 
  // this function will set obj.called, and then call the function whenever
  // the timeout eventually fires.
  var callfunc = function() { obj.called = true; f(); }; 
  // calling .extend(1000) will add 1000ms to the time and reset the timeout.
  // also, calling .extend(-1000) will remove 1000ms, setting timer to 0ms if needed
  obj.extend = function(ms) {
    // break early if it already fired
    if (obj.called || obj.canceled) return false; 
    // clear old timer, calculate new timer
    clearTimeout(obj.timeout);
    obj.firetime += ms;
    var newDelay = obj.firetime - new Date(); // figure out new ms
    if (newDelay < 0) newDelay = 0;
    obj.timeout = setTimeout(callfunc, newDelay);
    return obj;
  };
  // Cancel the timer...  
  obj.cancel = function() {
    obj.canceled = true;
    clearTimeout(obj.timeout);
  };
  // call the initial timer...
  obj.timeout = setTimeout(callfunc, delay);
  // return our object with the helper functions....
  return obj;
}

var d = +new Date();
var timer = setAdvancedTimer(function() { alert('test'+ (+new Date() - d)); }, 1000);

timer.extend(1000);
// should alert about 2000ms later