Detect when Scroll reaches the BOTTOM of the page [ without jQuery ]

Question

I want to alert something when the scroll reaches the BOTTOM of the page, like this:

$(function(){
  $(document).scroll(function() {
    if($(document).scrol         


        

Answer 1

document.onscroll = function() {
    if(!document.body.scrollTop){
        alert('top');
    }
}

JSFiddle demo