Minimal example of how to create a gnome shell extension that has a menu, menu items, and a label that updates on a timer

gnome-shell-menu-items-example.js

// Basic stuff
const St = imports.gi.St;
const Lang = imports.lang;

// UI specific components
const Main = imports.ui.main;
const PopupMenu = imports.ui.popupMenu;
const PanelMenu = imports.ui.panelMenu;

const Mainloop = imports.mainloop;

const Indicator = new Lang.Class({
    Name: 'GnomeBitBarIndicator', // TODO does this even matter?
    Extends: PanelMenu.Button,

    _init: function() {
        this.parent(0.0, "GnomeBitBar", false); // TODO does this even matter?

        // Set up click handlers
        this.actor.connect('enter_event', Lang.bind(this, this.resetCounter, true));
        this.actor.connect('leave_event', Lang.bind(this, this.resetCounter, false));
        this.actor.connect('button_press_event', Lang.bind(this, this.resetCounter, false));

        this.i = 0;
        this.text = new St.Label({
            text: "loading..."
        });
        this._refresh();
        this.actor.add_actor(this.text);

        // add menu items
        let item = new PopupMenu.PopupSubMenuMenuItem('Hello', true);
        this.menu.addMenuItem(item);
        
        // make the first menu item do something on click
        item.actor.connect('button_press_event', Lang.bind(this, function(){
            this.menu.close();
            this.resetCounter();
        }, false));

        // Add some extra items
        this.menu.addMenuItem(new PopupMenu.PopupSubMenuMenuItem('hello 2', false));
        this.menu.addMenuItem(new PopupMenu.PopupSubMenuMenuItem('hello 3', false));
        this.menu.addMenuItem(new PopupMenu.PopupSubMenuMenuItem('hello 4', false));
        this.menu.addMenuItem(new PopupMenu.PopupSubMenuMenuItem('hello 5', false));

        //add seperator menu
        this.menu.addMenuItem(new PopupMenu.PopupSeparatorMenuItem);

    },

    resetCounter: function(){
        this.i = 0;
    },

    updateUI: function() {
        this.text.set_text('i = ' + this.i);
    },

    _refresh: function () {
        this.i++;
        this.updateUI();
        this._removeTimeout();
        this._timeout = Mainloop.timeout_add_seconds(2, Lang.bind(this, this._refresh));
        return true;
    },

    _removeTimeout: function () {
        if (this._timeout) {
            Mainloop.source_remove(this._timeout);
            this._timeout = null;
        }
    }
});

let menu;

function init() {
    // One time startup initialization
}

function enable() {
    menu = new Indicator();
    Main.panel.addToStatusArea('indicator', menu);
}

function disable() {
    menu.destroy();
}