code: function scrollPage(to, offset, callback) {
    if ( offset === void 0 ) offset = 0;
  
    var startTime;
    var duration = 500;
    var startPos = window.pageYOffset;
    var endPos = ~~(to.getBoundingClientRect().top - offset);
    var scroll = function (timestamp) {
      var elapsed;
  
      startTime = startTime || timestamp;
      elapsed = timestamp - startTime;
  
      document.body.scrollTop = document.documentElement.scrollTop = easeInOutCubic(elapsed, startPos, endPos, duration);
  
      if (elapsed < duration) {
        requestAnimationFrame(scroll);
      } else if (callback) {
        callback.call(to);
      }
    };
  
    requestAnimationFrame(scroll);
  }
docs: Scroll the page to a particular page anchor
  @param {HTMLElement} to The element to scroll to.
  @param {number} offset A scrolling offset.
  @param {function} callback Function to apply after scrolling
  @return {void}