How do you know the scroll bar has reached bottom of a page

Question

I have a HTML page, when the scroll bar reaches bottom of the page I need to slide in a div from bottom-right containing an iframe.

Using JQuery I have implemented

Answer 1

$(window).scroll(function(){ // each time the scroll event is triggered
    if($(window).scrollTop() + screen.height > $('body').height()) {
        // if scroll has reached the bottom, execute this 
    }
};