Count characters in a textbox using Javascript

<script type="text/javascript">
function countChars(countfrom,displayto) {
  var len = document.getElementById(countfrom).value.length;
  document.getElementById(displayto).innerHTML = len;
}
</script>
<textarea id="data" cols="40" rows="5" onkeyup="countChars('data','charcount');" onkeydown="countChars('data','charcount');" onmouseout="countChars('data','charcount');"></textarea><br>
<span id="charcount">0</span> characters entered.