Střídání pozadí webu

        <script type="text/javascript">
 function run(interval, frames) {
    var int = 1;
    
    function func() {
        document.body.id = "b"+int;
        int++;
        if(int === frames) { int = 1; }
    }
    
    var swap = window.setInterval(func, interval);
}

run(3000, 3); //milliseconds, frames
        </script>

#b1 { background:url(../images/body_background_1.jpg) top center no-repeat; }
#b2 { background:url(../images/body_background_2.jpg) top center no-repeat; }