count down timer javascript code example

Example 1: html timer

<!DOCTYPE HTML>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
p {
  text-align: center;
  font-size: 60px;
  margin-top: 0px;
}
</style>
</head>
<body>

<p id="demo"></p>

<script>
// Set the date we're counting down to
var countDownDate = new Date("Jan 5, 2021 15:37:25").getTime();

// Update the count down every 1 second
var x = setInterval(function() {

  // Get today's date and time
  var now = new Date().getTime();
    
  // Find the distance between now and the count down date
  var distance = countDownDate - now;
    
  // Time calculations for days, hours, minutes and seconds
  var days = Math.floor(distance / (1000 * 60 * 60 * 24));
  var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
  var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
  var seconds = Math.floor((distance % (1000 * 60)) / 1000);
    
  // Output the result in an element with id="demo"
  document.getElementById("demo").innerHTML = days + "d " + hours + "h "
  + minutes + "m " + seconds + "s ";
    
  // If the count down is over, write some text 
  if (distance < 0) {
    clearInterval(x);
    document.getElementById("demo").innerHTML = "EXPIRED";
  }
}, 1000);
</script>

</body>
</html>

Example 2: working of timers in javascript

Timers are used to execute a piece of code at a set time or also to repeat the code in a given interval of time. 
This is done by using the functions 
1. setTimeout
2. setInterval
3. clearInterval

The setTimeout(function, delay) function is used to start a timer that calls a particular function after the mentioned delay. 
The setInterval(function, delay) function is used to repeatedly execute the given function in the mentioned delay and only halts when cancelled. 
The clearInterval(id) function instructs the timer to stop.

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Php Example