Changing Scrollbar Position

Question

Is it possible to change the scrollbar position when the user reaches a certain point scrolling down a web page? For example once you reached half way down down the page the

Answer 1

The three scrolling functions you'll want to concern yourself with are window.scroll(x,y), window.scrollBy(dx,dy), and window.scrollTo(x,y).

As David mentioned you'll need the scroll position to know where you are and use the window.onscroll event to fire off this calculation.