Creating a Timer In Javascript

by HSG on Nov 04, 2012 in JavaScript Tutorial

Javascript has a lot of features which are often overlooked by web developers, and one such feature is the ability to have timed events. If you do not understand what that means do not worry because all will be explained in this tutorial.

Timing events allow you to write code which will execute within a set amount of time. As an example, say you wanted to display a clock on your web page. You could use javascripts' built in timing functions to make the time change every second or every minute.

Of course there are other uses for such functions, but we will stick with a simple timer which creates a dialog box with the words Hi There on it every 3 seconds, that way you can get a feel for how to work with timing.

To get started we are going to need a basic web page. Just create a blank page and add the following code in the script tags:

setInterval(function(){alert("Hi There")},3000);

Once you have copied the code above and saved it in-between the body tags of your web page, go ahead and try to view the page. If you copied the code exactly as it is you will get a popup dialog box every 3 seconds with the words Hi There written on it.

Now the code its self is pretty easy to understand. On line one we use a script tag to tell the browser it is about to execute some javascript and we have a closing script tag at the end of the code block to make sure our code is actually executed. On line two we use javascripts built in function setInterval and if you look closely you will see that it takes two parameters.

The first parameter is an anonymous function which actually creates the dialog box with our string of text. The second parameter is an integer which tells the browser how long it should wait before the code is executed again.

Time in any programming language is measured in milliseconds so as you can see from the code above 3 seconds is written as 3000, likewise if you wanted to make your script wait for 10 seconds you would write it as 10000.

There are a multitude of ways you can use the ability to time events in your code, and the best way to discover them is by experimenting. Do not be afraid to play around with the code and put it to another use.

Javascript got a bad reputation a few years back for other people misusing its ability to create pop-up windows, and most of us avoid websites with unnecessary pop-up's so use the code presented here only if it has a real world use, otherwise you run the risk of people clicking away from your web site and never coming back.

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