extension.js

const St = imports.gi.St;
const Gio = imports.gi.Gio;

const ExtensionUtils = imports.misc.extensionUtils;
const Me = ExtensionUtils.getCurrentExtension();
const Main = imports.ui.main;
const PanelMenu = imports.ui.panelMenu;

class Extension {
  constructor() {
    this._indicator = null;
  }

  enable() {
    log(`enabling ${Me.metadata.name}`);

    let indicatorName = `${Me.metadata.name} Indicator`;

    // Create a panel button
    this._indicator = new PanelMenu.Button(0.0, indicatorName, false);

    // Add an icon
    let icon = new St.Icon({
      gicon: new Gio.ThemedIcon({ name: "face-laugh-symbolic" }),
      style_class: "system-status-icon",
    });
    this._indicator.add_child(icon);

    // `Main.panel` is the actual panel you see at the top of the screen,
    // not a class constructor.
    Main.panel.addToStatusArea(indicatorName, this._indicator);
  }

  // REMINDER: It's required for extensions to clean up after themselves when
  // they are disabled. This is required for approval during review!
  disable() {
    log(`disabling ${Me.metadata.name}`);

    this._indicator.destroy();
    this._indicator = null;
  }
}

function init() {
  log(`initializing ${Me.metadata.name}`);

  return new Extension();
}