javascript: pause setTimeout();

If I have an active timeout running that was set through var t = setTimeout("dosomething()", 5000),

Is there anyway to pause and resume it?

---

Is there any way to get the time remaining on the current timeout?
or do I have to in a variable, when the timeout is set, store the current time, then we we pause, get the difference between now and then?

You could wrap window.setTimeout like this, which I think is similar to what you were suggesting in the question:

var Timer = function(callback, delay) {
    var timerId, start, remaining = delay;

    this.pause = function() {
        window.clearTimeout(timerId);
        timerId = null;
        remaining -= Date.now() - start;
    };

    this.resume = function() {
        if (timerId) {
            return;
        }

        start = Date.now();
        timerId = window.setTimeout(callback, remaining);
    };

    this.resume();
};

var timer = new Timer(function() {
    alert("Done!");
}, 1000);

timer.pause();
// Do some stuff...
timer.resume();

Something like this should do the trick.

function Timer(fn, countdown) {
    var ident, complete = false;

    function _time_diff(date1, date2) {
        return date2 ? date2 - date1 : new Date().getTime() - date1;
    }

    function cancel() {
        clearTimeout(ident);
    }

    function pause() {
        clearTimeout(ident);
        total_time_run = _time_diff(start_time);
        complete = total_time_run >= countdown;
    }

    function resume() {
        ident = complete ? -1 : setTimeout(fn, countdown - total_time_run);
    }

    var start_time = new Date().getTime();
    ident = setTimeout(fn, countdown);

    return { cancel: cancel, pause: pause, resume: resume };
}

No. You'll need cancel it (clearTimeout), measure the time since you started it and restart it with the new time.

A slightly modified version of Tim Downs answer. However, since Tim rolled back my edit, I've to answer this myself. My solution makes it possible to use extra arguments as third (3, 4, 5...) parameter and to clear the timer:

function Timer(callback, delay) {
    var args = arguments,
        self = this,
        timer, start;

    this.clear = function () {
        clearTimeout(timer);
    };

    this.pause = function () {
        this.clear();
        delay -= new Date() - start;
    };

    this.resume = function () {
        start = new Date();
        timer = setTimeout(function () {
            callback.apply(self, Array.prototype.slice.call(args, 2, args.length));
        }, delay);
    };

    this.resume();
}

As Tim mentioned, extra parameters are not available in IE lt 9, however I worked a bit around so that it will work in oldIE's too.

Usage: new Timer(Function, Number, arg1, arg2, arg3...)

function callback(foo, bar) {
    console.log(foo); // "foo"
    console.log(bar); // "bar"
}

var timer = new Timer(callback, 1000, "foo", "bar");

timer.pause();
document.onclick = timer.resume;

"Pause" and "resume" don't really make much sense in the context of setTimeout, which is a one-off thing. You might want to pause a chained series of setTimeout calls, in which case just don't schedule the next one (perhaps cancel the one that's outstanding via clearTimeout, as below). But setTimeout itself doesn't loop, there's nothing to pause and resume.

If you mean setInterval then no, you can't pause it, you can only cancel it (clearInterval) and then re-schedule it again. Details of all of these in the Timers section of the spec.

// Setting
var t = setInterval(doSomething, 1000);

// Pausing (which is really stopping)
clearInterval(t);
t = 0;

// Resuming (which is really just setting again)
t = setInterval(doSomething, 1000);

The Timeout was easy enough to find a solution for, but the Interval was a little bit trickier.

I came up with the following two classes to solve this issues:

function PauseableTimeout(func, delay){
    this.func = func;

    var _now = new Date().getTime();
    this.triggerTime = _now + delay;

    this.t = window.setTimeout(this.func,delay);

    this.paused_timeLeft = 0;

    this.getTimeLeft = function(){
        var now = new Date();

        return this.triggerTime - now;
    }

    this.pause = function(){
        this.paused_timeLeft = this.getTimeLeft();

        window.clearTimeout(this.t);
        this.t = null;
    }

    this.resume = function(){
        if (this.t == null){
            this.t = window.setTimeout(this.func, this.paused_timeLeft);
        }
    }

    this.clearTimeout = function(){ window.clearTimeout(this.t);}
}

function PauseableInterval(func, delay){
	this.func = func;
	this.delay = delay;
	
	this.triggerSetAt = new Date().getTime();
	this.triggerTime = this.triggerSetAt + this.delay;
	
	this.i = window.setInterval(this.func, this.delay);
	
	this.t_restart = null;
	
	this.paused_timeLeft = 0;
	
	this.getTimeLeft = function(){
		var now = new Date();
		return this.delay - ((now - this.triggerSetAt) % this.delay);
	}
	
	this.pause = function(){
		this.paused_timeLeft = this.getTimeLeft();
		window.clearInterval(this.i);
		this.i = null;
	}
	
	this.restart = function(sender){
		sender.i = window.setInterval(sender.func, sender.delay);
	}
	
	this.resume = function(){
		if (this.i == null){
			this.i = window.setTimeout(this.restart, this.paused_timeLeft, this);
		}
	}
	
	this.clearInterval = function(){ window.clearInterval(this.i);}
}

These can be implemented as such:

var pt_hey = new PauseableTimeout(function(){
    alert("hello");
}, 2000);

window.setTimeout(function(){
    pt_hey.pause();
}, 1000);

window.setTimeout("pt_hey.start()", 2000);

This example will set a pauseable Timeout (pt_hey) which is scheduled to alert, "hey" after two seconds. Another Timeout pauses pt_hey after one second. A third Timeout resumes pt_hey after two seconds. pt_hey runs for one second, pauses for one second, then resumes running. pt_hey triggers after three seconds.

Now for the trickier intervals

var pi_hey = new PauseableInterval(function(){
    console.log("hello world");
}, 2000);

window.setTimeout("pi_hey.pause()", 5000);

window.setTimeout("pi_hey.resume()", 6000);

This example sets a pauseable Interval (pi_hey) to write "hello world" in the console every two seconds. A timeout pauses pi_hey after five seconds. Another timeout resumes pi_hey after six seconds. So pi_hey will trigger twice, run for one second, pause for one second, run for one second, and then continue triggering every 2 seconds.

OTHER FUNCTIONS

• clearTimeout() and clearInterval()

  pt_hey.clearTimeout(); and pi_hey.clearInterval(); serve as an easy way to clear the timeouts and intervals.

• getTimeLeft()

  pt_hey.getTimeLeft(); and pi_hey.getTimeLeft(); will return how many milliseconds till the next trigger is scheduled to occur.

/revive

ES6 Version using Class-y syntactic sugar 

(slightly-modified: added start())

class Timer {
  constructor(callback, delay) {
    this.callback = callback
    this.remainingTime = delay
    this.startTime
    this.timerId
  }

  pause() {
    clearTimeout(this.timerId)
    this.remainingTime -= new Date() - this.startTime
  }

  resume() {
    this.startTime = new Date()
    clearTimeout(this.timerId)
    this.timerId = setTimeout(this.callback, this.remainingTime)
  }

  start() {
    this.timerId = setTimeout(this.callback, this.remainingTime)
  }
}

// supporting code
const pauseButton = document.getElementById('timer-pause')
const resumeButton = document.getElementById('timer-resume')
const startButton = document.getElementById('timer-start')

const timer = new Timer(() => {
  console.log('called');
  document.getElementById('change-me').classList.add('wow')
}, 3000)

pauseButton.addEventListener('click', timer.pause.bind(timer))
resumeButton.addEventListener('click', timer.resume.bind(timer))
startButton.addEventListener('click', timer.start.bind(timer))

<!doctype html>
<html>
<head>
  <title>Traditional HTML Document. ZZz...</title>
  <style type="text/css">
    .wow { color: blue; font-family: Tahoma, sans-serif; font-size: 1em; }
  </style>
</head>
<body>
  <h1>DOM &amp; JavaScript</h1>

  <div id="change-me">I'm going to repaint my life, wait and see.</div>

  <button id="timer-start">Start!</button>
  <button id="timer-pause">Pause!</button>
  <button id="timer-resume">Resume!</button>
</body>
</html>

I needed to calculate the elapsed and remaining time to show a progress-bar. It was not easy using the accepted answer. 'setInterval' is better than 'setTimeout' for this task. So, I created this Timer class that you can use in any project.

https://jsfiddle.net/ashraffayad/t0mmv853/

'use strict';
    
     
    //Constructor
    var Timer = function(cb, delay) {
      this.cb = cb;
      this.delay = delay;
      this.elapsed = 0;
      this.remaining = this.delay - self.elapsed;
    };
    
    console.log(Timer);
    
    Timer.prototype = function() {
      var _start = function(x, y) {
          var self = this;
          if (self.elapsed < self.delay) {
            clearInterval(self.interval);
            self.interval = setInterval(function() {
              self.elapsed += 50;
              self.remaining = self.delay - self.elapsed;
              console.log('elapsed: ' + self.elapsed, 
                          'remaining: ' + self.remaining, 
                          'delay: ' + self.delay);
              if (self.elapsed >= self.delay) {
                clearInterval(self.interval);
                self.cb();
              }
            }, 50);
          }
        },
        _pause = function() {
          var self = this;
          clearInterval(self.interval);
        },
        _restart = function() {
          var self = this;
          self.elapsed = 0;
          console.log(self);
          clearInterval(self.interval);
          self.start();
        };
    
      //public member definitions
      return {
        start: _start,
        pause: _pause,
        restart: _restart
      };
    }();
    
    
    // - - - - - - - - how to use this class
    
    var restartBtn = document.getElementById('restart');
    var pauseBtn = document.getElementById('pause');
    var startBtn = document.getElementById('start');
    
    var timer = new Timer(function() {
      console.log('Done!');
    }, 2000);
    
    restartBtn.addEventListener('click', function(e) {
      timer.restart();
    });
    pauseBtn.addEventListener('click', function(e) {
      timer.pause();
    });
    startBtn.addEventListener('click', function(e) {
      timer.start();
    });

Typescript implementation based on top rated answer

/** Represents the `setTimeout` with an ability to perform pause/resume actions */
export class Timer {
    private _start: Date;
    private _remaining: number;
    private _durationTimeoutId?: NodeJS.Timeout;
    private _callback: (...args: any[]) => void;
    private _done = false;
    get done () {
        return this._done;
    }

    constructor(callback: (...args: any[]) => void, ms = 0) {
        this._callback = () => {
            callback();
            this._done = true;
        };
        this._remaining = ms;
        this.resume();
    }

    /** pauses the timer */
    pause(): Timer {
        if (this._durationTimeoutId && !this._done) {
            this._clearTimeoutRef();
            this._remaining -= new Date().getTime() - this._start.getTime();
        }
        return this;
    }

    /** resumes the timer */
    resume(): Timer {
        if (!this._durationTimeoutId && !this._done) {
            this._start = new Date;
            this._durationTimeoutId = setTimeout(this._callback, this._remaining);
        }
        return this;
    }

    /** 
     * clears the timeout and marks it as done. 
     * 
     * After called, the timeout will not resume
     */
    clearTimeout() {
        this._clearTimeoutRef();
        this._done = true;
    }

    private _clearTimeoutRef() {
        if (this._durationTimeoutId) {
            clearTimeout(this._durationTimeoutId);
            this._durationTimeoutId = undefined;
        }
    }

}

You could look into clearTimeout()

or pause depending on a global variable that is set when a certain condition is hit. Like a button is pressed.

  <button onclick="myBool = true" > pauseTimeout </button>

  <script>
  var myBool = false;

  var t = setTimeout(function() {if (!mybool) {dosomething()}}, 5000);
  </script>

You could also implement it with events.

Instead of calculating the time difference, you start and stop listening to a 'tick' event which keeps running in the background:

var Slideshow = {

  _create: function(){                  
    this.timer = window.setInterval(function(){
      $(window).trigger('timer:tick'); }, 8000);
  },

  play: function(){            
    $(window).bind('timer:tick', function(){
      // stuff
    });       
  },

  pause: function(){        
    $(window).unbind('timer:tick');
  }

};

If you're using jquery anyhow, check out the $.doTimeout plugin. This thing is a huge improvement over setTimeout, including letting you keep track of your time-outs with a single string id that you specify and that doesn't change every time you set it, and implement easy canceling, polling loops & debouncing, and more. One of my most-used jquery plugins.

Unfortunately, it doesn't support pause/resume out of the box. For this, you would need to wrap or extend $.doTimeout, presumably similarly to the accepted answer.

I needed to be able to pause setTimeout() for slideshow-like feature.

Here is my own implementation of a pausable timer. It integrates comments seen on Tim Down's answer, such as better pause (kernel's comment) and a form of prototyping (Umur Gedik's comment.)

function Timer( callback, delay ) {

	/** Get access to this object by value **/
	var self = this;



	/********************* PROPERTIES *********************/
	this.delay = delay;
	this.callback = callback;
	this.starttime;// = ;
	this.timerID = null;


	/********************* METHODS *********************/

	/**
	 * Pause
	 */
	this.pause = function() {
		/** If the timer has already been paused, return **/
		if ( self.timerID == null ) {
			console.log( 'Timer has been paused already.' );
			return;
		}

		/** Pause the timer **/
		window.clearTimeout( self.timerID );
		self.timerID = null;	// this is how we keep track of the timer having beem cleared

		/** Calculate the new delay for when we'll resume **/
		self.delay = self.starttime + self.delay - new Date().getTime();
		console.log( 'Paused the timer. Time left:', self.delay );
	}


	/**
	 * Resume
	 */
	this.resume = function() {
		self.starttime = new Date().getTime();
		self.timerID = window.setTimeout( self.callback, self.delay );
		console.log( 'Resuming the timer. Time left:', self.delay );
	}


	/********************* CONSTRUCTOR METHOD *********************/

	/**
	 * Private constructor
	 * Not a language construct.
	 * Mind var to keep the function private and () to execute it right away.
	 */
	var __construct = function() {
		self.starttime = new Date().getTime();
		self.timerID = window.setTimeout( self.callback, self.delay )
	}();	/* END __construct */

}	/* END Timer */

Example:

var timer = new Timer( function(){ console.log( 'hey! this is a timer!' ); }, 10000 );
timer.pause();

To test the code out, use timer.resume() and timer.pause() a few times and check how much time is left. (Make sure your console is open.)

Using this object in place of setTimeout() is as easy as replacing timerID = setTimeout( mycallback, 1000) with timer = new Timer( mycallback, 1000 ). Then timer.pause() and timer.resume() are available to you.

function delay (ms)   {  return new Promise(resolve => setTimeout(resolve, s));  }

"async" working demo at: site zarsoft.info

You can do like below to make setTimeout pausable on server side (Node.js)

const PauseableTimeout = function(callback, delay) {
    var timerId, start, remaining = delay;

    this.pause = function() {
        global.clearTimeout(timerId);
        remaining -= Date.now() - start;
    };

    this.resume = function() {
        start = Date.now();
        global.clearTimeout(timerId);
        timerId = global.setTimeout(callback, remaining);
    };

    this.resume();
};

and you can check it as below

var timer = new PauseableTimeout(function() {
    console.log("Done!");
}, 3000);
setTimeout(()=>{
    timer.pause();
    console.log("setTimeout paused");
},1000);

setTimeout(()=>{
    console.log("setTimeout time complete");
},3000)
    
setTimeout(()=>{
    timer.resume();
    console.log("setTimeout resume again");
},5000)

If anyone wants the TypeScript version shared by the Honorable @SeanVieira here, you can use this:

    public timer(fn: (...args: any[]) => void, countdown: number): { onCancel: () => void, onPause: () => void, onResume: () => void } {
        let ident: NodeJS.Timeout | number;
        let complete = false;
        let totalTimeRun: number;
        const onTimeDiff = (date1: number, date2: number) => {
            return date2 ? date2 - date1 : new Date().getTime() - date1;
        };

        const handlers = {
            onCancel: () => {
                clearTimeout(ident as NodeJS.Timeout);
            },
            onPause: () => {
                clearTimeout(ident as NodeJS.Timeout);
                totalTimeRun = onTimeDiff(startTime, null);
                complete = totalTimeRun >= countdown;
            },
            onResume: () => {
                ident = complete ? -1 : setTimeout(fn, countdown - totalTimeRun);
            }
        };

        const startTime = new Date().getTime();
        ident = setTimeout(fn, countdown);

        return handlers;
    }

I don't think you'll find anything better than clearTimeout. Anyway, you can always schedule another timeout later, instead 'resuming' it.

If you have several divs to hide, you could use an setInterval and a number of cycles to do like in:

<div id="div1">1</div><div id="div2">2</div>
<div id="div3">3</div><div id="div4">4</div>
<script>
	function hideDiv(elm){
		var interval,
			unit = 1000,
			cycle = 5,
			hide = function(){
				interval = setInterval(function(){
					if(--cycle === 0){
						elm.style.display = 'none';
						clearInterval(interval);
					}
					elm.setAttribute('data-cycle', cycle);
					elm.innerHTML += '*';
				}, unit);
			};
		elm.onmouseover = function(){
			clearInterval(interval);
		};
		elm.onmouseout = function(){
			hide();
		};
		hide();
	}
	function hideDivs(ids){
		var id;
		while(id = ids.pop()){
			hideDiv(document.getElementById(id));
		}
	}
	hideDivs(['div1','div2','div3','div4']);
</script>