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JavaScript features a couple of methods that lets you run a piece of JavaScript code (javascript function) at some point in the future. These methods are:


In this tutorial, I'll explain how setTimetout() method works, and give a real world example. You may find the details of setInterval() method in JavaScript setInterval Function - JavaScript Timing Events

setTimeout()

window.setTimeout() method allows you to specify a piece of JavaScript code (expression) will be run after specified number of miliseconds from when the setTimeout() method is called.

Syntax

var t = setTimeout ( expression, timeout );

The setTimeout() method returns a numeric timeout ID which can be used to refer the timeout to use with clearTimeout method. The first parameter (expression) of setTimeout() is a string containing a javascript statement. The statement could be a call to a JavaScript function like "delayedAlert();" or a  statement like "alert('This alert is delayed.');". The second parameter (timeout), indicates the number of miliseconds to pass before executing the expression.

Example 

<html>
   <head>
      <script type="text/javascript">
        function delayedAlert()
        {
           var t=setTimeout("alert('You pressed the button 5 seconds ago!')",5000)
        }
      </script>
   </head>
   <body>
      <form>
         <input type="button" value="Display Delayed Alert"
                onClick="delayedAlert();">
      </form>
   </body>
</html>

An alert box will be shown 5 seconds later when you clicked the button.

clearTimeout()

Sometimes it's useful to be able to cancel a timer before it goes off. The clearTimeout() method lets us do exactly that. Its syntax is:

clearTimeout ( timeoutId );

where timeoutId is the ID of the timeout as returned from the setTimeout() method call.

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Comments

November 21. 2007 05:13

You state that the "first parameter (expression) of setTimeout() is a string containing a javascript statement" - while setTimeout and setInterval do allow you to do this, you can pass a function pointer or an anonymous function in as well (and perhaps that would be better anyway - strings as code is a nice feature, but can get ugly). So, here are examples of both:

function Foo{
   // do something
}
setTimeout(Foo, 100);

or

setTimeout(function(){
   // do something here
}, 100);

Jason Bunting | Reply

October 27. 2009 14:28

Thank you for your help!

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December 26. 2009 19:27

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February 10. 2010 13:25

Useful info. Hope to see more good posts in the future.

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