For the checkboxes there are three methods to change the checked/
unchecked-state:
Check:
$.jstree._reference('#mytree').check_node('#id-of-node');
Uncheck:
$.jstree._reference('#mytree').uncheck_node('#id-of-node');
Toggle check:
$.jstree._reference('#mytree').change_state('#id-of-node');
The state "undetermined" is in my opinion only for showing that some
(not all) child-nodes of the node are checked. There's no method to
set it directly as "undetermined".
But if really needed, you can change the css-class to make it look as
"undetermined":
$('#id-of-node').removeClass('jstree-checked jstree-
unchecked').addClass('jstree-undetermined');
But this will NOT result in any changes about the 'state' of the node/
checkbox recognized by the checkbox-plugin!!
Markus.