if (!Element.prototype.matches)
  Element.prototype.matches = Element.prototype.msMatchesSelector ||
    Element.prototype.webkitMatchesSelector;

if (!Element.prototype.closest)
  Element.prototype.closest = function(s) {
    var el = this;
    if (!document.documentElement.contains(el)) return null;
    do {
      if (el.matches(s)) return el;
      el = el.parentElement || el.parentNode;
    } while (el !== null);
    return null;
  };