Limit number of characters allowed

Enter text (max length is 20 characters):

<script type="text/javascript">

function limitlength(obj, length){
var maxlength=length
if (obj.value.length>maxlength)
obj.value=obj.value.substring(0, maxlength)
}

</script>

Enter text (max length is 20 characters):
<form>
<textarea onkeyup="return limitlength(this, 20)" style="width: 300px; height: 90px"></textarea>
</form>