Detect when scroll reaches bottom of window.

scroll-to-bottom.js

export function scrolledToBottom(window, marginFromBottom = 0) {
  const documentBody = window.document.body;
  const documentElement = window.document.documentElement;

  const scrollTop =
    (documentElement && documentElement.scrollTop) || documentBody.scrollTop;

  const scrollHeight =
    (documentElement && documentElement.scrollHeight) ||
    documentBody.scrollHeight;

  const clientHeight = documentElement.clientHeight || window.innerHeight;

  const bottomReached =
    Math.ceil(scrollTop + clientHeight + marginFromBottom) >= scrollHeight;

  return bottomReached;
}