var js_elements = {}; //elementy, ktorych hodnoty sledujeme

function js_focus(el) {
  if (!js_elements[el.id]) {
    js_elements[el.id] = el.value;
    el.value = '';
  } else {
    if (el.value == js_elements[el.id]) {
      el.value = '';
    }
  }
}

function js_blur(el) {
  if (el.value == '') el.value = js_elements[el.id];
}