檢測是否捲動到頁面底部

scroll_to_bottom.js

window.addEventListener('scroll', function() {
  var pageHeight = document.documentElement.offsetHeight;
  var windowHeight = window.innerHeight;
  var scrollPosition = window.scrollY || window.pageYOffset || document.body.scrollTop + (document.documentElement && document.documentElement.scrollTop || 0);

  console.log({pageHeight, windowHeight, scrollPosition});

  if (pageHeight <= windowHeight + scrollPosition) {
    console.log('At the bottom');
  }
});