Q1456 How come in long running loops, the form fields do not get set before the loop begins?

<form name="form1">
<input type="text" name="test1">
</form>

<script language="JavaScript"><!--
function f_start() {
  j=0;
  //setting form field before loop
  document.form1.test1.value="Counting";
  setTimeout('longLoop()',10);
}

function longLoop() {
  for (i=0; i<=1000000; i++,j++) ;
}
//--</script>