helloworld.js

#!/usr/bin/env gjs

const Lang = imports.lang;
const GLib = imports.gi.GLib;
const GObject = imports.gi.GObject;

let Helloworld = Lang.Class({
    Name: "Helloworld",
    Extends: GObject.Object,
    _init: function() {
        GObject.Object.prototype._init.call(this);
        this.mainloop = imports.mainloop;
    },
    __idle_cb: function() {
        print("hello world");
        this.mainloop.quit();
    },
    run: function() {
        this.mainloop.idle_add(Lang.bind(this, this.__idle_cb));
        this.mainloop.run();
    }
});

let helloworld = new Helloworld();
helloworld.run();