perké non funziona?



<HTML>
<HEAD>
<META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
<META content="Notepad" name=GENERATOR>

</HEAD>
<BODY>

<script language="javascript" type="text/javascript">
function DoTheCheck(num) {
var id;
id = num;
alert('num=' + num
alert('id=' + id
if(document.form1.checkbox[id].checked == true){ alert('box0 is checked'); }

if(document.form1.checkbox[id].checked == false){ alert('box1 is not checked'); }

}

</script>

<form id="form1" name="form1" method="post" action="ddd.asp">
<input type="checkbox" name="checkbox" id="checkbox" onclick="DoTheCheck(1)">
<input type="checkbox" name="checkbox" id="checkbox" onclick="DoTheCheck(2)">
<input type="checkbox" name="checkbox" id="checkbox" onclick="DoTheCheck(3)">
</form>
</BODY>
</HTML>