gecko-dev/dom/serviceworkers/test/eventsource/eventsource_worker_helper.js

function ok(aCondition, aMessage) {
  return new Promise(function (resolve, reject) {
    self.clients.matchAll().then(function (res) {
      if (!res.length) {
        reject();
        return;
      }
      res[0].postMessage({
        status: "callback",
        data: "ok",
        condition: aCondition,
        message: aMessage,
      });
      resolve();
    });
  });
}