egIcon.js

#!/usr/bin/gjs

/*
GJS example showing how to build Gtk javascript applications
setting the application icon from the 'assets' folder and if
not available from the 'stock icons'

Run it with:
    gjs egIcon.js
*/

const Gio   = imports.gi.Gio;
const GLib  = imports.gi.GLib;
const Gtk   = imports.gi.Gtk;
const Lang  = imports.lang;

// Get application folder and add it into the imports path
function getAppFileInfo() {
    let stack = (new Error()).stack,
        stackLine = stack.split('\n')[1],
        coincidence, path, file;

    if (!stackLine) throw new Error('Could not find current file (1)');

    coincidence = new RegExp('@(.+):\\d+').exec(stackLine);
    if (!coincidence) throw new Error('Could not find current file (2)');

    path = coincidence[1];
    file = Gio.File.new_for_path(path);
    return [file.get_path(), file.get_parent().get_path(), file.get_basename()];
}
const path = getAppFileInfo()[1];
imports.searchPath.push(path);

const App = function () { 
    this.title = 'Example Icon';
    GLib.set_prgname(this.title);
};

App.prototype.run = function (ARGV) {

    this.application = new Gtk.Application();
    this.application.connect('activate', () => { this.onActivate(); });
    this.application.connect('startup', () => { this.onStartup(); });
    this.application.run([]);
};

App.prototype.onActivate = function () {

    this.window.show_all();
};

App.prototype.onStartup = function() {

    this.buildUI();
};

App.prototype.buildUI = function() {

    let result = false,
        str = ' In Wayland there is no \n such thing as a window icon, \n the application icon must \n be set from the .desktop file';

    this.window = new Gtk.ApplicationWindow({ application: this.application,
                                              title: this.title,
                                              default_height: 200,
                                              default_width: 200,
                                              window_position: Gtk.WindowPosition.CENTER });
    try {
        this.window.set_icon_from_file(path + '/assets/appIcon.png');
    } catch (err) {
        this.window.set_icon_name('application-x-executable');
    }
    log(str);

    this.label = new Gtk.Label({ label: str });
    this.window.add(this.label);
};

//Run the application
let app = new App();
app.run(ARGV);