rx-unzip.js

return RxFb.api(FB_APP_ID, FB_CLIENT_ID, "/me?fields=email", { access_token: fbToken; }).flatMap(fbUser -> {
    var userQuery = new Parse.Query(Parse.User);
    userQuery.equalTo("email", fbUser.email);
    return Observable.unzip(fbToken, ParseObservable.find(userQuery)); // magic
  }).switchIfEmpty(fbToken -> {
    var newUser = new Parse.User();
    newUser.setUsername(fbUser.email);
    newUser.setEmail(fbUser.email)
    newUser.setPassword(fbToken);
    return ParseObservable.signUp(newUser);
  })
  .flatMap(parseUser -> ParseObservable.fetch(parseUser))
  .map(parseUser -> parseUser.getSessionToken());