function esDigito(sChr){ 
  var sCod = sChr.charCodeAt(0); 
  return ((sCod > 47) && (sCod < 58)); 
}
function valSep(oTxt){ 
  var bOk = false; 
  var sep1 = oTxt.charAt(2); 
  var sep2 = oTxt.charAt(5); 
  bOk = bOk || ((sep1 == '-') && (sep2 == '-')); 
  bOk = bOk || ((sep1 == '/') && (sep2 == '/')); 
  return bOk; 
} 
function finMes(oTxt){ 
  var nMes = parseInt(oTxt.substr(3, 2), 10); 
  var nAno = parseInt(oTxt.substr(6), 10); 
  var nRes = 0; 
  switch (nMes){ 
   case 1: nRes = 31; break; 
   case 2: nRes = 28; break; 
   case 3: nRes = 31; break; 
   case 4: nRes = 30; break; 
   case 5: nRes = 31; break; 
   case 6: nRes = 30; break; 
   case 7: nRes = 31; break; 
   case 8: nRes = 31; break; 
   case 9: nRes = 30; break; 
   case 10: nRes = 31; break; 
   case 11: nRes = 30; break; 
   case 12: nRes = 31; break; 
 } 
  return nRes + (((nMes == 2) && (nAno % 4) == 0)? 1: 0); 
} 
function valDia(oTxt){ 
  var bOk = false; 
  var nDia = parseInt(oTxt.substr(0, 2), 10); 
  bOk = bOk || ((nDia >= 1) && (nDia <= finMes(oTxt))); 
  return bOk; 
} 
function valMes(oTxt){ 
  var bOk = false; 
  var nMes = parseInt(oTxt.substr(3, 2), 10); 
  bOk = bOk || ((nMes >= 1) && (nMes <= 12)); 
  return bOk; 
} 
function valAno(oTxt){ 
  var bOk = true; 
  var nAno = oTxt.substr(6); 
  bOk = bOk && ((nAno.length == 2) || (nAno.length == 4)); 
  if (bOk){ 
    for (var i = 0; i < nAno.length; i++){ 
       bOk = bOk && esDigito(nAno.charAt(i)); 
    } 
  } 
   return bOk; 
} 

function comprobar_data(nom_form,nom_camp,camp_error){
	var oTxt = eval('document.'+ nom_form +'.'+ nom_camp +'.value');
	var bOk = true; 
	if (oTxt != ''){ 
	   bOk = bOk && (valAno(oTxt)); 
	   bOk = bOk && (valMes(oTxt)); 
	   bOk = bOk && (valDia(oTxt)); 
	   bOk = bOk && (valSep(oTxt)); 
	   if (!bOk){ 
		 alert(eval('document.'+ nom_form +'.'+ camp_error +'.value'));
		 eval('document.'+ nom_form +'.'+ nom_camp +'.select()');
	   } else eval('document.'+ nom_form +'.submit()');
	} else {
	  eval('document.'+ nom_form +'.submit()');
	}
}