This question already has an answer here:
Is there any way in javascript to check if web page has been vertically scrolled? specially for Internet Explorer? I need to get the mouse position in IE but using jQuery event e.pageY it gives correct value when page is not scrolled but when page is scrolled down then it gives wrong position.
In case any future googlers find this, the quick example is:
Check out this question if you are comfortable with using jQuery:
How do I determine height and scrolling position of window in jQuery?