turn callback into return.js

async function loadAuthInstance() {
  const load = new Promise(function(resolve, reject) {
    gapi.load('auth2', resolve);
  });
  return load.then(async () => {
    return await window.gapi.auth2
      .init({
        client_id: 'client-id-apparently',
      })
      .then(authInstance => {
        window.authInstance = authInstance;
      });
  });
}