giusta osservazione! Questa funziona anche per prezzi inferiori all'euro

codice:
<html>
<head>
<script>
function format(number) {
    
    number = String(number);
    
    while (number.length < 3) {
        number = "0" + number;
    }
    
    formatted = number.replace(/\d*?(\d{2})$/, ",$1");
    number = number.replace(/(\d*?)\d{2}$/, "$1");

    while (number.length > 3) {
      formatted = number.replace(/\d*?(\d{3})$/, ".$1") + formatted;
      number = number.replace(/(\d*?)\d{3}$/, "$1");
    }
   
    formatted = number + formatted;
    return formatted;

}
</script>
</head>
<body>
<script>
document.write(format(01));
</script>
</body>
</html>