Actions and signals

Gtk has a set of predefined events that you can use in your application.

Declare HelloWorld as a new class.

class HelloWorld {

constructor is called when a new instance is created. Create a GtkApplication, then connect activate to the existing Gtk event _onActivate and startup to _onStartup:

    constructor() {
        this.application = new Gtk.Application();
        this.application.connect('activate', this._onActivate.bind(this));
        this.application.connect('startup', this._onStartup.bind(this));

Show the window upon application activation:

    _onActivate() {