How can i determine the position of textarea cursor relative to the window in x,y?

I am trying to create a javascript code editor just for lear开发者_开发技巧ning and I am doing a great job so far. The only thing is that I wanna place the autocomplete box in a position relative to the text cursor in textarea. So how can I determine the cursor position relative to the upper left corner of the window ?

Something else please, how can i capture the tab & enter keys press in a textarea ?

I am using a semi-transparent textarea (semi to keep the cursor blinking) with underlying div to enable code highlighting later on. Is this the best technique to do that ? Or there is a way to make textarea accept rich text or HTML ?

I suspect that you can do all that without a textarea. Read up on the contentEditable property. Here's a demo. This is how the Google Docs editor is implemented, incidentally. And here's a stackoverflow question dealing with finding the cursor position in a contentEditable div.