codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Conta box</title>
<script type="text/javascript">
<!--
function ContaBox(){
var count=0;
var box = document.getElementsByTagName("input")
for(var i=0; i<box.length; i++){
if(box[i].type=="checkbox" && box[i].checked){
count++;}
document.getElementById("conta").innerHTML=count;
if(count!=5){
document.getElementById("invia").setAttribute("disabled","disabled");
}else{document.getElementById("invia").removeAttribute("disabled");
}
}
}
onload=function(){ContaBox();}
//-->
</script>
</head>
<body>
<h1 style="text-align:center"> Form box </h1>
<form name="form1" action="" id="form1" onsubmit="InviaMail();return false;
" method="post" enctype="text/plain">
<input type="checkbox" name="b1" id="b1" onclick="ContaBox()" />
box1
<input type="checkbox" name="b2" id="b2" onclick="ContaBox()" />
box2
<input type="checkbox" name="b3" id="b3" onclick="ContaBox()" />
box3
<input type="checkbox" name="b4" id="b4" onclick="ContaBox()" />
box4
<input type="checkbox" name="b5" id="b5" onclick="ContaBox()" />
box5
<input type="checkbox" name="b6" id="b6" onclick="ContaBox()" />
box6
</p>
<div id="conta"></div>
<input name="invia" id="invia" type="submit" value="Invia" /></form>
</body>
</html>