Suppose I have a Div that fills only part of my screen, but it has a vertical scrollbar because it has lots of text contents.

When the user clicks a button, I want to know where the thumb of the scrollbar is - is it at the beginning, the end, or maybe 30% through the content?

I thought I could use "scrollHeight" in my calculations, but that seems wrong - in my tests I find its a huge number.

How can the task be accomplished?