reduce_promise-chaining.js

const getUser = (email) => fetch(`/api/${email}`).then(res => res.json());

const promiseQueue = (values, func) => {
  const reducer = (promises, value) =>
    promises.then((promise) => func(value).then(res => promise.push(res) && res));

  return values.reduce(reducer, Promise.result([]));
};

promiseQueue(["test@example.com", "another@example.com", "thirdOne@example.com"], getUser);