#!/usr/bin/gjs

imports.gi.versions.Gtk = '3.0'

const Gtk = imports.gi.Gtk;

class Application {

    //create the application

    constructor() {

        this.application = new Gtk.Application();

       //connect to 'activate' and 'startup' signals to handlers.

       this.application.connect('activate', this._onActivate.bind(this));

       this.application.connect('startup', this._onStartup.bind(this));

    }

    //create the UI

    _buildUI() {

        this._window = new Gtk.ApplicationWindow({ application: this.application,

                                                   title: "Hello World!" });

        this._window.set_default_size(200, 200);

        this.label = new Gtk.Label({ label: "Hello World" });

        this._window.add(this.label);

    }

    //handler for 'activate' signal

    _onActivate() {

        //show the window and all child widgets

        this._window.show_all();

    }

    //handler for 'startup' signal

    _onStartup() {

        this._buildUI();

    }

};

//run the application

let app = new Application();

app.application.run(ARGV);