getExternalIpAddress.js

#!/usr/bin/env gjs

const { GLib, GUPnP } = imports.gi;

const { MainLoop } = GLib;

const mainloop = new MainLoop(null, true);

function getExternalIpAddress() {
  // does it work with interface: null or without
  const context = new GUPnP.Context({ port: 0, interface: "enp0s31f6" });
  context.init(null); // needed?

  const controlPoint = new GUPnP.ControlPoint({
    client: context,
    //
    target: "urn:schemas-upnp-org:service:WANIPConnection:2",
  });

  controlPoint.connect("service-proxy-available", (self, serviceProxy) => {
    log("service proxy available");

    const [success, NewExternalIPAddress] = serviceProxy.send_action_list(
      // action
      "GetExternalIPAddress",
      // in_name
      [],

      // in_values
      [],

      // out_names
      ["NewExternalIPAddress"],

      // out_types
      [imports.gi.GObject.TYPE_STRING],
    );

    log(success);
    log(NewExternalIPAddress);
  });

  controlPoint.set_active(true);
}

getExternalIpAddress();

mainloop.run();