How can one define / manipulate the selection of textarea in Safari from JavaScript?

I have JavaScript code that does two things:

• extracts the selected text from the text area
• adds a prefix and suffix to the selected text

Currently, the code uses the properties of the selectionStart

and the selectionEnd

textbox to figure out where the selection starts / ends, extracts the selection text and processes it, and then re-writes the textbox value with the prefix and suffix inserted in the correct places.

This implementation works fine in Firefox , but it doesn't work in Safari . Apparently, properties selectionStart

and selectionEnd

do not exist in WebKit. (I suspect the code also doesn't work in Google Chrome, which is also WebKit-based, although I haven't tested that.)

How can I accomplish these two operations in Safari?