Wie wird das gemacht?

<div id="box" style="background:#008800;position:absolute;display:none"></div>
 
<script type="text/javascript">
// ===========================
// (C) 2009 Matthias Glaessner
// ===========================
 
var v         = 1;    // speed
var maxpos    = 100;  // Max scrolling Pos X
var btop      = 200;  // BOX Position Y
var bheight   = 160;  // BOX Height
var isRUNNING = 0;    // Running and direction
var tm;               // Timeout
 
function create() {
  var b = document.getElementById("box").style;
  b.left    = -maxpos    + "px";
  b.width   = (maxpos+v) + "px";
  b.top     = btop       + "px";
  b.height  = bheight    + "px";
  b.display = "block";
}
 
function mm(e) {
  e = e || window.event;
 
  if (e.pageX <= maxpos) {  if (isRUNNING!=1) {isRUNNING=1; animate(); } }
  else  {  if (isRUNNING!=-1) {isRUNNING=-1; animate(); } }
}
 
function animate() {
  var cx = parseInt(document.getElementById("box").style.left) + v * isRUNNING;
  if (cx<=0 && cx>=-maxpos) {
    document.getElementById("box").style.left = cx + "px";
    tm = window.setTimeout("animate()",10);
  } else {
    window.clearTimeout(tm);
    isRUNNING = 0;
  }
}
 
create();
document.onmousemove = mm;
</script>