Dear Boris,
Just to keep you are informed, 'if(has_capability('...'))' , also known as legacy capability, has become obsolete in the advanced versions of Moodle. You may preferably do this with the predefined moodle function, as shown below:
global $USER;
$context = context_user::instance($USER->id);
Or
$context = get_context_instance(CONTEXT_MODULE, $cm->id); //where $cm->id is the course module id
$roles = get_user_roles($context, $USER->id, true);
foreach($roles as $role => $roleVal) {
if($roleVal->roleid == 5) {
// write your popup code here
}
}
Note:- By default the role id for student is 5. To confirm the role id refer to mdl_role table in your Moodle instance database.
To get various contexts of users with respect to courses you may refer to the following link:-
http://docs.moodle.org/dev/Access_API
Kindly let me know if this is useful.
Keep moodling
Purnendu
DualCube