How o clear undo buffer/list of textarea

[Happy MAnocha]

Hii All,
i m facing one problem hope u cud help me.
I am using Textarea and i added some buttons on that like bold, italic
, undo ,redo etc.
for all of the above actions i m using document.execCommand("bold"),
document.execCommand("italic"); document.execCommand("undo");,
(Javascript)document.execCommand("redo"); now i want to add one more
button "clear undo list" it should work like when i made some changes
to textarea and then press this button and after that if i press undo
button it should not work.i hope u got the Question.
can u suggest that how can i clear the undo butffer or undo list in
javascript.
hope to hear from u soon..
Thanks