Reset Undo on the tinymce editor

I have one editor where I switch between content in one editor, and what I want to do when I set the new content, I would like to reset the undo possibility.

I have read on this site http://www.tinymce.com/wiki.php/api4:class.tinymce.UndoManager

That it’s just to call tinymce.UndoManager.clear() but I just get that the function is undefined.

The global variable tinyMCE has an array of editors. So you have to call the undoManager inside them. Like this for default wp editor on post edit/create screen:

tinyMCE.editors[0].undoManager.clear();

If you want to do it in a specific editor, select the editor id in n like this:

var n = 0; // editor id
tinyMCE.editors[n].undoManager.clear();