Javascript Timer Example

The aim of this example is to explain the timing events in javascript.

The javascript window.setTimeout(function, milliseconds) function is used to execute a function, after waiting a specified number of milliseconds. This method returns a timeout id.

Notice, setTimeout and window.setTimeout are essentially the same, the only difference being that in the second statement we are referencing the setTimeout method as a property of the global window object.

The javascript clearTimeout(timeoutID) function is used to stop the given timer.

Following tips are very important when working with this function

  • The function is only executed once. If you need to repeat execution, use the setInterval() method.
  • Use the clearTimeout() method to prevent the function from running.


First of all you need to create a simple html documents.


<!DOCTYPE html>
	<title>javascript timer example</title>


2. Javascript Timer Examples

2.1 Show alert after 3 seconds

This example sets a timer to call the given method after 3 seconds. As you can notice, the setTimeout(function, milliseconds) function takes two parameters, the first is the method name and the second is the interval time in milliseconds.

Click a button. Wait 3 seconds, and the page will alert “Hello”:

<button onclick="setTimeout(myFunction, 3000)">Try it</button>

	function myFunction() {

The result in the browser would be:

Show alert after 2 seconds
Show alert after 3 seconds

2.2 Stop javascript timer

The javascript clearTimeout(timeoutID) is used to stop the timer by using the given timeoutID. The javascript setTimeout(function, milliseconds) function returns a timeout id that can be passed to this method.

<button onclick="myVar = setTimeout(myFunction, 2000)">Try it</button>
<button onclick="clearTimeout(myVar)">Stop it</button>

	function myFunction() {

The result in the browser would be:

Stop javascript timer
Stop javascript timer

2.3 O’clock example

As you can notice, in the line 4 of the following javascript code, we call the startTime() method to show o’clock and set a timer. This timer will call the startTime() method after a half of second. That will help us to update the o’clock values.

<div id="txt"></div>

	function startTime() {
		var today = new Date();
		var h = today.getHours();
		var m = today.getMinutes();
		var s = today.getSeconds();
		// add a zero in front of numbers<10
		m = checkTime(m);
		s = checkTime(s);
		document.getElementById("txt").innerHTML = h + ":" + m + ":" + s;
		var t = setTimeout(function(){ startTime() }, 500);

	function checkTime(i) {
		if (i < 10) {
			i = "0" + i;
		return i;

The result in the browser would be:

O'clock example
O’clock example

4. Download the Source Code

Download: You can download the full source code of this example here: Javascript Timer Example

Saeb Najim

Saeb has graduated from the University of Technology. During the last ten years (since 2005) he has been involved with a large number of projects about programming, software engineering, design and analysis . He works as a senior Software Engineer in the e-commerce and web development sector where he is mainly responsible for projects based on Java, Java frameworks, design patterns and Big Data technologies.
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