Controllo caratteri testo form

[danix]

nell'head
<script language="JavaScript" type="text/javascript">

function conta(val) {
max=100
if (val.testo.value.length > max) {
val.testo.value = val.testo.value.substring(0,max)
rest = 0
}
else {
rest = max - val.testo.value.length
}
val.num.value = rest
}
</SCRIPT>


nel body
<form name="pippo">
<textarea name="testo" rows="4" cols="30" wrap="soft" onKeyUp="conta(this.form)"></textarea>
<input value="100" size="3" name="num" disabled>
</form>