Auto expanding textarea

<script src="jquery.js"></script>

<script>
$(document).ready(function(){
$('#wer').scroll(function () {
old_height = document.getElementById("wer").style.height;
document.getElementById("wer").style.height = parseInt(old_height)+10+"px";
});

});
</script>


<textarea style="widows:15px; height:50px;" id="wer">asda sd</textarea>