The following JS script doesn't show the event types : 

const Lang = imports.lang;
const Gdk = imports.gi.Gdk;
const Gtk = imports.gi.Gtk;

Gtk.init(null, null);

let w = new Gtk.Window();
w.resize(800, 600);

let box = new Gtk.Box();
w.add(box);

let eb = new Gtk.EventBox({ });
eb.events = Gdk.EventMask.BUTTON_PRESS_MASK;
box.pack_start(eb, true, true, 0);

eb.connect('event', Lang.bind(this, function(widget, event) {
        log('type : ' + event.type);
        return true;
}));

w.show_all();
Gtk.main();