Using Timers in JavaScript - Window Washer
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Let's start at the top, with the setTimeout() and clearTimeout() methods. These methods belong to the Window object, and are commonly used to run a particular piece of code after a pre-defined interval has passed. Consider the following example:
<script language="JavaScript">
var t = window.setTimeout('alert("5 seconds have passed since you loaded
this page")', 5000);
</script>
In this case, the setTimeout() method is used to run the function 5000 milliseconds (5 seconds). Thus, there are always two arguments to the setTimeout() method; the first is the code to run, and the second is the amount of time to wait before running it.
Here's another, more useful example.
<script language="JavaScript">
var t = setTimeout('window.close()', 30000);
</script>
In this one, the window (which we'll assume has been popped open from some other parent window) closes automatically 30 seconds after it opens.
Just as you can set a timeout, you can also clear it with the clearTimeout() method. This method is used to remove a timeout previously declared with setTimeout(). Since there may be multiple calls to setTimeout() in the same document, it is mandatory to provide clearTimeout() with a reference so that it knows which timeout to clear. The following variant of the example above demonstrates:
<script language="JavaScript">
var t = window.setTimeout('window.close()', 30000);
window.clearTimeout(t);
</script>
In this case, the window will never close, because the clearTimeout() method will cancel the timeout previously created with setTimeout().
If you want to really obfuscate, you can clear a timeout after a specified interval, by wrapping the call to clearTimeout() in a call to setTimeout():
<script language="JavaScript">
var t = window.setTimeout('window.close()', 30000);
var c = window.setTimeout('window.clearTimeout(t)', 10000);
</script>
In this case too, the window will never close, because the first timeout will be cancelled 10 seconds in by the call to clearTimeout() in the second.
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