Puoi provare questo

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
var stopUserAction=false;

function userAction () {
 if (stopUserAction) {
  return;
 }
 document.getElementById("pippo").innerHTML +="*"
 res = document.getElementById("pippo").innerHTML
 if (res == "******************************") {
  document.getElementById("pippo").innerHTML =" "
 } 
 setTimeout("userAction ()",10);
} // function userAction ()

//-->
</script>

</head>
<body onload="userAction()">
<div id="pippo"></div>


<input type="button" value="Stop" onclick="stopUserAction=true">
</body>
</html>