codice:
<body onload="sum()">
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
<p id="demo2">Punti </p>
n1 <input type = "number" id = "n1" min="0" max="5" value="0" onchange="sum()"/>
n2 <input type = "number" id = "n2" min="0" max="5" value="0" onchange="sum()" />
n3 <input type = "number" id = "n3" min="0" max="5" value="0" onchange="sum()" />
n4 <input type = "number" id = "n4" min="0" max="5" value="0" onchange="sum()" />
n5 <input type = "number" id = "n5" min="0" max="5" value="0" onchange="sum()" />
<br>
<input type="submit" id="form" value="Allenati" disabled="disabled">
</form>
<script type="text/javascript">
function sum()
{
var tot, num1, num2, num3, num4, num5, dif, result;
tot = 5;
num1 = parseInt(document.getElementById("n1").value, 10);
num2 = parseInt(document.getElementById("n2").value, 10);
num3 = parseInt(document.getElementById("n3").value, 10);
num4 = parseInt(document.getElementById("n4").value, 10);
num5 = parseInt(document.getElementById("n5").value, 10);
dif = (num1+num2+num3+num4+num5);
result = (tot - dif);
document.getElementById("demo2").innerHTML = result;
if(result == 0)
{
document.getElementById("form").disabled = false;
}
}
</script>
</body>
è un codice molto spartano ma a me basta che sia funzionale ^^