Simple sticky nav in plain JS

sticky-nav.js

// Simple sticky nav in plain JS
// p.s. this is just a short example, you should remember to debounce the scroll event ;-)
if ("addEventListener" in window && "classList" in document.documentElement) {

  var element = document.getElementById("nav"),
    offset = element.offsetTop;

  window.addEventListener("scroll", function() {
    if (offset < window.pageYOffset) {
      element.classList.add("fixed");
    } else {
      element.classList.remove("fixed");
    }
  }, false);

}