How can I get keyboard cursor(caret) position in javascript?

Hi. I have a question.

How can I get keyboard cursor(caret) position in javascript?

I made a multilined edittext in ScriptUI.

But It's not working about Enter key.

All I want is when I push 'enter' key, begin a new line.

If I know how to get keyboard cursor position, I can insert '\n' character in middle of sentances.

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var win =new Window ("dialog", '');

          win.orientation = "column";

var grpContents = win.add("group")

          var codeInput = grpContents.add ("edittext", [0, 0, 150, 550], "", {multiline:true});

                    codeInput.alignment = ['fill', 'top']

                    codeInput.active = true;

                   codeInput.onEnterKey = function(){

            codeInput.text = codeInput.text+"\n"

     }

          win.show()

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I use windowsXP and Illustrator CS3.

If you know about that, please help me!~