Code for a simple JavaScript countdown timer?

var count=30;var counter=setInterval(timer, 1000); //1000 will  run it every 1 secondfunction timer(){  count=count-1;  if (count <= 0)  {     clearInterval(counter);     //counter ended, do something here     return;  }  //Do code for showing the number of seconds here}

To make the code for the timer appear in a paragraph (or anywhere else on the page), just put the line:

<span id="timer"></span>

where you want the seconds to appear. Then insert the following line in your timer() function, so it looks like this:

function timer(){  count=count-1;  if (count <= 0)  {     clearInterval(counter);     return;  } document.getElementById("timer").innerHTML=count + " secs"; // watch for spelling}

I wrote this script some time ago:

Usage:

var myCounter = new Countdown({      seconds:5,  // number of seconds to count down    onUpdateStatus: function(sec){console.log(sec);}, // callback for each second    onCounterEnd: function(){ alert('counter ended!');} // final action});myCounter.start();

function Countdown(options) {  var timer,  instance = this,  seconds = options.seconds || 10,  updateStatus = options.onUpdateStatus || function () {},  counterEnd = options.onCounterEnd || function () {};  function decrementCounter() {    updateStatus(seconds);    if (seconds === 0) {      counterEnd();      instance.stop();    }    seconds--;  }  this.start = function () {    clearInterval(timer);    timer = 0;    seconds = options.seconds;    timer = setInterval(decrementCounter, 1000);  };  this.stop = function () {    clearInterval(timer);  };}

So far the answers seem to rely on code being run instantly. If you set a timer for 1000ms, it will actually be around 1008 instead.

Here is how you should do it:

function timer(time,update,complete) {    var start = new Date().getTime();    var interval = setInterval(function() {        var now = time-(new Date().getTime()-start);        if( now <= 0) {            clearInterval(interval);            complete();        }        else update(Math.floor(now/1000));    },100); // the smaller this number, the more accurate the timer will be}

To use, call:

timer(    5000, // milliseconds    function(timeleft) { // called every step to update the visible countdown        document.getElementById('timer').innerHTML = timeleft+" second(s)";    },    function() { // what to do after        alert("Timer complete!");    });