JavaScript Automatically Move Cursor to Next Field When Textbox Full

<html
xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>JavaScript to automatically move from one field to another field</title>
<script type="text/javascript">
function movetoNext(current, nextFieldID) {
if (current.value.length >= current.maxLength) {
document.getElementById(nextFieldID).focus();
}
}
</script>
</head>
<body>
<b>Enter your Text:</b>
<input type="text" id="first" size="4" onkeyup="movetoNext(this, 'second')" maxlength="3" />
<input type="text" id="second" size="4" onkeyup="movetoNext(this, 'third')" maxlength="3" />
<input type="text" id="third" size="5" maxlength="4" />
</body>
</html>