Hello Ruizma,
Thanks for writing and for your interest in our products. Our products employ a slightly different approach when using Javascript - we have what we call CSOM - Client Side Object Model. This way, you can get the instance of the editor and use the set/getText methods to do that.
For example:
var oEditor = iged_getById(editorId);
if (oEditor)
oEditor.setText( cleanXhtml( oEditor.getText() ) );
A very good forum topic, where one of our customers has managed to create a client-side javascript XHTML filter and shared his solution with us, is located here:
http://forums.infragistics.com/forums/p/2428/15702.aspx#15702
More info on CSOM can be found here (our online help - the last link from the treeview on the left):
http://help.infragistics.com/NetAdvantage/NET/2008.2/CLR2.0/