// fade out

function fadeOut(el){
  el.style.opacity = 1;

  (function fade() {
    if ((el.style.opacity -= .1) < 0) {
      el.style.display = "none";
    } else {
      requestAnimationFrame(fade);
    }
  })();
}

// fade in

function fadeIn(el){
  el.style.opacity = 0;
  el.style.display = "block";

  (function fade() {
    var val = parseFloat(el.style.opacity);
    if (!((val += .1) > 1)) {
      el.style.opacity = val;
      requestAnimationFrame(fade);
    } 
  })();
}