Javascript text replacement

[Rogare]

I am making a "text editor" of HTML (doesn't matter why) and I have button that add HTML code to the end of the text field (in a form). I know that there is the "select" command that selects a part in the text field (or all of it), is there an opposite command that find out what part is selected?

Also, is there a command that can find where is the little stick that shows you where the new text you'll write will be? (in a text field, the user sees... Maybe it is also called a cursor? I dunno!)