SubDoLubDub

const SubDoLubDub = (client, stanzas) => {
  const types = stanzas.utils;

  const Event = stanzas.define({
    name: '_event',
    element: 'event',
    fields: {
      node: types.attribute('node'),
    },
  });

  const Subscribe = stanzas.define({
    name: 'mucsub',
    namespace: 'urn:xmpp:mucsub:0',
    element: 'subscribe',
    fields: {
      nick: types.attribute('nick'),
      events: types.multiExtension(Event),
    }
  });

  stanzas.withIQ((IQ) => {
    stanzas.extend(IQ, Subscribe);
  });
};

const client = XMPP.createClient({
  ...
});

client.use(SubDoLubDub);