Following code was provided to me @ http://jsfiddle.net/rUbwq/2/

1. $(window).scroll(function(){
2.     if(this.pageYOffset + $(this).height() > $(document).height() - 200){
3.         $('div').css('background', 'red'); //do popup
4.     }
5. });​

in response to my question of triggering a popup when scroller reached particular height...

Problem is this part:

1. this.pageYOffset + $(this).height()

why used $ in the 2nd this but not the first?