Cross browser body scrollTop

index.js

function getScrollTop() {
  return (isBlink || isSafari || isEdge) ? document.body.scrollTop
                                         : document.documentElement.scrollTop;
}

function setScrollTop(scrollTop) {
  if (isBlink || isSafari || isEdge) {
    document.body.scrollTop = scrollTop;
  } else {
    document.documentElement.scrollTop = scrollTop;
  }
}