gistfile1.js

// Let's see this in action. Consider a lowly div
//   ( wrap it in JQuery with $('div') ):

// how many pixels of content have been viewed
//   (already scrolled + current view)?
// formula : scrollTop + outerHeight

  $('div').scrollTop() + $('div').outerHeight();
    
// how many pixels are left to scroll?
// formula : scrollHeight - (scrollTop + outerHeight)

  $('div')[0].scrollHeight - ($('div').scrollTop + $('div').outerHeight);

// have we scrolled to the bottom?
// formula : scrollHeight / (scrollTop + outerHeight),
//   a value of 1 means scrolled to bottom.

  var element = $('div');
  var percent_scrolled = element[0].scrollHeight /
    (element.scrollTop() + element.outerHeight());
  var answer = percent_scrolled == 1;