Get scroll bottom; returns number

get_scroll_bottom.js

(()=>{
  function getScrollAmount(){
    const doc = document.documentElement;

    return {
      left: (window.pageXOffset || doc.scrollLeft) - (doc.clientLeft || 0),
      top: (window.pageYOffset || doc.scrollTop)  - (doc.clientTop || 0)
    };
  }

  function getScrollMax(){
    const scrollAmount = getScrollAmount();

    return {
      right: window.innerWidth + scrollAmount.left,
      bottom: window.innerHeight + getScrollAmount().top
    };
  }

  function getScrollBottom(){
    return getScrollMax().bottom;
  }

  return getScrollBottom();
})();