Get the content of the text area without post

Hello,
I try to get the content of the textarea, I work with xajax.
The buttom code :

<... onclick = "xajax_insertnews(getElementById(\'FCKeditor1\').value);"/>

This return the value defined at the begining :

$oFCKeditor->Value= "Contenu de l'article";

But not the modifications of the content of the text area, I've seen I need to use GetxHTML but I've don't totally understand how to do this, can someone help me please?

Thanks.

(I'm sorry for my english it's not my language).