function validateFormOnSubmit(theForm) {
var reason = "";

  reason += validateEmpty(theForm.nombre);
  reason += validateEmail(theForm.mail);
  reason += validateEmpty(theForm.telefono);
  reason += validateEmpty(theForm.comentarios);
    
  if (reason != "") {
    alert("Falta completar los campos marcados.\n" + reason);
    return false;
  }

  return true;
}
function validateEmpty(fld) {
    var error = "";
 
    if (fld.value.length == 0) {
        fld.style.background = '#dceaef'; 
        error = ""
    } else {
        fld.style.background = 'White';
    }
    return error;  
}

function trim(s)
{
  return s.replace(/^\s+|\s+$/, '');
}

function validateEmail(fld) {
    var error="";
    var tfld = trim(fld.value);                        // value of field with whitespace trimmed off
    var emailFilter = /^[^@]+@[^@.]+\.[^@]*\w\w$/ ;
    var illegalChars= /[\(\)\<\>\,\;\:\\\"\[\]]/ ;
   
    if (fld.value == "") {
        fld.style.background = '#dceaef';
        error = "No especificaste direccion de correo.\n";
    } else if (!emailFilter.test(tfld)) {              //test email for illegal characters
        fld.style.background = '#dceaef'
        error = "Por favor escribe una direccion valida de correo.\n";
    } else if (fld.value.match(illegalChars)) {
        fld.style.background = '#dceaef';
        error = "La direccion de correo tiene caracteres invalidos.\n";
    } else {
        fld.style.background = 'White';
    }
    return error;
}