tieni:

Codice PHP:

<html>
<head>
<title></title>
<script language="javascript">
<!--

function Invia(){
var qt1 = document.myForm.qt1.value;
var desc1 = document.myForm.desc1.value;
var costo1 = document.myForm.costo1.value;


if((qt1=="")||(desc1=="")||(costo1=="")){
   alert("errore!");
}
else 
   document.myForm.submit();
}

//-->
</script>
</head>
<body>
<form name="myForm" method="post" action="quello_che_vuoi">
<input type="text" name="qt1">
<input type="text" name="desc1">
<input type="text" name="costo1">
<input type="button" value="Invia" onClick="Invia()">
</form>