Prova cosi:
codice:
function check_valid(theForm) {
for (i=0; i < theForm.elements.length; i++) {
if (theForm.elements[i].value == "" && theForm.elements[i].className == "si") {
alert (theForm.elements[i].name + ": campo vuoto non accettabile");
theForm.elements[i].value = "";
theForm.elements[i].focus();
return false;
}else if (theForm.elements[i].type=="checkbox" && theForm.elements[i].checked && theForm.elements[i].className == "si") {
alert (theForm.elements[i].name + ": campo non spuntato");
theForm.elements[i].focus();
return false;
}
}
}