Can I see if a timer is still running?

Simple question here that I can't seem to find an answer for: Once a setTimeout is set, is there any way to see if it's still, well, set?

if (!Timer)
{
    Timer = setTimeout(DoThis,60000);
}

From what I can tell, when you clearTimeout, the variable remains at its last value. A console.log I just looked at shows Timer as being '12', no matter if the timeout has been set or cleared. Do I have to null out the variable as well, or use some other variable as a boolean saying, yes, I have set this timer? Surely there's a way to just check to see if the timeout is still running... right? I don't need to know how long is left, just if it's still running.

Answers:

Answer

There isn't anyway to interact with the timer except to start it or stop it. I typically null the timer variable in the timeout handler rather than use a flag to indicate that the timer isn't running. There's a nice description on W3Schools about how the timer works. In their example they use a flag variable.

The value you are seeing is a handle to the current timer, which is used when you clear (stop) it.

Answer

What I do is:

var timer = null;

if (timer != null) {
  window.clearTimeout(timer); 
  timer = null;
}
else {
  timer = window.setTimeout(yourFunction, 0);
}
Answer

There is no need to check for an existing timer, just execute clearTimeout before starting the timer.

var timer;
//..
var startTimer = function() {
  clearTimeout(timer);
  timer = setTimeout(DoThis, 6000);
}

This will clear any timer before starting a new instance.

Answer

Set another variable Timer_Started = true with your timer. And also change the variable to false when the timer function is called:

// set 'Timer_Started' when you setTimeout
var Timer_Started = true;
var Timer = setTimeout(DoThis,60000);

function DoThis(){

   // function DoThis actions 
   //note that timer is done.
   Timer_Started = false;

}

function Check_If_My_Timer_Is_Done(){

   if(Timer_Started){
      alert("The timer must still be running.");
   }else{
      alert("The timer is DONE.");
   }

}
Answer

I know this is a necroposting but i think still people are looking for this.

This is what i use: 3 variables:

  1. t for milliseconds since.. in Date Object for next target
  2. timerSys for the actual interval
  3. seconds threshold for milliseconds has been set

next i have a function timer with 1 variable the function checks if variable is truly, if so he check if timer is already running and if this is the case than fills the global vars , if not truly, falsely, clears the interval and set global var timerSys to false;

var t, timerSys, seconds;

function timer(s) {
  if (s && typeof s === "number") {
    if (typeof timerSys === "boolean" || typeof timerSys === "undefined") {
      timerSys = setInterval(function() {
        sys();
      }, s);
      t = new Date().setMilliseconds(s);
      seconds = s;
    }
  } else {
    clearInterval(timerSys);
    timerSys = false;
  }
  return ((!timerSys) ? "0" : t)
}

function sys() {
  t = new Date().setMilliseconds(seconds);

}

Example I

Now you can add a line to sys function:

function sys() {
  t = new Date().setMilliseconds(seconds);
  console.log("Next execution: " + new Date(t));
//this is also the place where you put functions & code needed to happen when interval is triggerd

}

And execute :

  timer(5000);

Every 5 seconds in console:

  //output:: Next execution: Sun May 08 2016 11:01:05 GMT+0200 (Romance (zomertijd))

Example II

function sys() {
  t = new Date().setMilliseconds(seconds);
  console.log("Next execution: " + seconds/1000 + " seconds");

}

$(function() {
  timer(5000);
});

Every 5 seconds in console:

      //output:: Next execution: 5 seconds

Example III

var t, timerSys, seconds;

function timer(s) {
  if (s && typeof s === "number") {
    if (typeof timerSys === "boolean" || typeof timerSys === "undefined") {
      timerSys = setInterval(function() {
        sys();
      }, s);
      t = new Date().setMilliseconds(s);
      seconds = s;
    }
  } else {
    clearInterval(timerSys);
    timerSys = false;
  }
  return ((!timerSys) ? "0" : t)
}

function sys() {
  t = new Date().setMilliseconds(seconds);
  console.log("Next execution: " + seconds / 1000 + " seconds");

}

$(function() {
  timer(5000);

  $("button").on("click", function() {
    $("span").text(t - new Date());
  })
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button>Freebeer</button>
<span></span>

Note this way you can go below 0

Answer

I usually nullify the timer:

var alarm = setTimeout(wakeUpOneHourLater, 3600000);
function wakeUpOneHourLater() {
    alarm = null;    //stop alarm after sleeping for exactly one hour
}
//...
if (!alarm) {
    console.log('Oops, waked up too early...Zzz...');
}
else {
    console.log('Slept for at least one hour!');
}

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