function getCookie(c_name)
{
  if (document.cookie.length>0) {
    c_start = document.cookie.indexOf(c_name + "=");
    if (c_start!=-1) {
      c_start = c_start + c_name.length + 1;
      c_end = document.cookie.indexOf(";", c_start);
      if (c_end == -1) c_end = document.cookie.length;
      return unescape(document.cookie.substring(c_start,c_end));
    }
  }
  return null;
}

document.cookie = 'testcookie=1';
if (getCookie('testcookie') != 1) alert('Włącz mechanizm cookies!');