Validar formulário em Javascript

<script language="javascript" type="text/javascript">
function valida(formulario){
var total = formulario.elements.length;
i = 0
while (i <= total)
{
if(formulario.elements[i].value == ""){
//    alert("O campo " + formulario.elements[i].name + "  continua vazio.");
formulario.elements[i].focus();
return false;
break;
}
i++
}
}
</script>
<form onSubmit="return valida(this);">