The Book of JavaScript, 2nd Edition

setInterval() [FF, IE 4]

Executes JavaScript statements at repeated time intervals, given two parameters: the JavaScript statements to execute and the number of milliseconds between each execution. The function returns a reference to the interval so that clearInterval() may cancel it.

For example:

var the_interval = setInterval("alert('Stop procrastinating!');", 10000);

creates an interval that calls up an alert box every 10 seconds.