when user scroll some position then auto loading data ...

autoLoading.js

handleAppend() {
  const top = window.pageYOffset ||
    document.documentElement.scrollTop ||
    document.body.scrollTop;
    
  if (!isEmpty(data)
    && (top + window.innerHeight) / document.body.scrollHeight > 0.9
    && !isloading // false
  ) {
    //do something ...
  }
}

window.addEventListener('scroll', handleAppend, false); //listen the `scroll` event.

window.removeEventListener('scroll', handleAppend, false); //remove the `scroll` event.