// Lectura de cookie
function readCookie(name)
{
  var ca = document.cookie.split(';');
 
  var nameEQ = name + "=";
  for(var i=0; i < ca.length; i++) {
    var c = ca[i];
    while (c.charAt(0)==' ') c = c.substring(1, c.length); //delete spaces
    if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length, c.length);
 
    }
  return null;
}