function is_bool (mixed_var) {
  // http://kevin.vanzonneveld.net
  // +   original by: Onno Marsman
  // +   improved by: CoursesWeb (http://www.coursesweb.net/)
  // *     example 1: is_bool(false);
  // *     returns 1: true
  // *     example 2: is_bool(0);
  // *     returns 2: false
  return (mixed_var === true || mixed_var === false); // Faster (in FF) than type checking
}

is_bool(false);

true

is_bool(0);

false