如何判断滚动条何时位于asp.net多行文本框的底部

I am working on an asp.net page and I have a multiline text box that displays some text. I want the user to have to scroll all the way to the bottom before I display a checkbox for them to continue. My question is how can you tell if the scroll bar is at the bottom?I am working on an asp.net page and I have a mu