Penso ti puo' essere utile.
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled</title>
</head>
<body>
<script language="JavaScript"><!--
function handler(e) {
var key = (navigator.appName == "Netscape") ? e.which : e.keyCode;
if (key == 8 || key == 110 || key == 188 || key == 190 || (key > 47 && key < 58) || (key > 95 && key < 107)) return true; else return false;
}
function scanDigits(e) {
var key = (navigator.appName == "Netscape") ? e.which : e.keyCode;
if (key == 8) {return true}
b = String.fromCharCode(key);
aValue = document.getElementById('textfield2').value + b;
espressione = /^[0-9]+[\.|,]{0,1}[0-9]*$/;
if (espressione.exec(aValue)!= null) {
return true;
}
return false;
}
//--></script>
<input type="text" name="textfield" onKeyDown="return handler(event);">
<input type="text" id="textfield2" onkeypress="return scanDigits(event);">
</body>
</html>