Save & restore scroll position

save-restore-scroll-position.js

(function() {

  var position

  function saveScrollPosition() {
    // If we don’t already have a saved scroll position
    if (position == null || position <= 0) {
      position = window.scrollY
    }
  }

  function restoreScrollPosition() {
    // If we have a saved scroll position, and if we’re at the top of the page
    if (position != null && position > 0 && window.scrollY <= 0) {
      window.scrollTo(0, position)

      // Reset the saved scroll position      
      position = null
    }
  }

  window.__saveScrollPosition    = saveScrollPosition
  window.__restoreScrollPosition = restoreScrollPosition

})();