The EE global only has username and shouldn't be relied upon as it's not a formal documented method to get information (and so could change or be manipulated).
If you're already writing a module/extension (a "plugin" is frontend only), then output your JavaScript from there instead of relying on the "CP CSS & JS" extension.
You can access all the user information via the session class:
ee()->session->userdata['screen_name'];
ee()->session->userdata['email'];
ee()->session->userdata['username'];
Add your own external JS file:
ee()->add_js_script('file', 'insert filename here');
The Docs on the CP class can be found here. Full Developer documentation here.
Consider using an Extension hook to inject your javascript - this would probably be the easiest route.
Note: These classes are automatically available from within your module/extension and don't have to be loaded.