JavaScript getTimeout?

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

Answer 2

I believe not. A better approach might be to write your own wrapper which stores your timers (func-ref, delay, and timestamp). That way you can pretend to update a timer by clearing it and calculate a copy with an updated delay.

Answer 3

Another wrapper:

function SpecialTimeout(fn, ms) {
    this.ms = ms;
    this.fn = fn;
    this.timer = null;
    this.init();
}

SpecialTimeout.prototype.init = function() {
    this.cancel();
    this.timer = setTimeout(this.fn, this.ms);
    return this;
};

SpecialTimeout.prototype.change = function(ms) {
    this.ms += ms;
    this.init();
    return this;
};

SpecialTimeout.prototype.cancel = function() {
    if ( this.timer !== null ) {
        clearTimeout(this.timer);
        this.timer = null;
    }
    return this;
};

Usage:

var myTimer = new SpecialTimeout(function(){/*...*/}, 10000);

myTimer.change(-5000); // Retard by five seconds
myTimer.change(5000); // Extend by five seconds
myTimer.cancel(); // Cancel
myTimer.init(); // Restart

myTimer.change(1000).init(); // Chain!

Answer 4

It may be not exactly what you want, but take a look anyway, maybe you can use it to your benefit.

There is a great solution written by my ex-coworker that can create special handler functions that can stop and start timeouts when required. It is most widely used when you need to create a small delay for hover events. Like when you want to hide a mouseover menu not exactly at the time when a mouse leaves it, but a few milliseconds later. But if a mouse comes back, you need to cancel the timeout.

The solution is a function called getDelayedHandlers. For example you have a function that shows and hides a menu

function handleMenu(show) {
    if (show) {
        // This part shows the menu
    } else {
        // This part hides the menu
    }
}

You can then create delayed handlers for it by doing so:

var handlers = handleMenu.getDelayedHandlers({
    in: 200, // 'in' timeout
    out: 300, // 'out' timeout
});

handlers becomes an object that contains two handler functions that when being called cancel the other one's timeout.

var element = $('menu_element');
element.observe('mouseover', handlers.over);
element.observe('mouseout', handlers.out);

P.S. For this solution to work you need to extend the Function object with the curry function, which is automatically done in Prototype.

Answer 5

One possibility can be like this:

if (this condition true)
{
  setTimeout(function, 5000);
}
elseif (this condition true)
{
  setTimeout(function, 10000);
}
else
{
  setTimeout(function, 1000);
}

It's up to your how you construct your conditions or the logic. thanks