Promise.all, but wait for all promises to finish

README.md

Promise.all will execute all promises in parallel, and fail whenever any one of the promises fails. This could even include failing synchronously if one is a Promise.reject(). Instead of doing this, here we want to make sure that all promises finish before we handle the result. We wait for all promises to finish, check their status, and reject or resolve the final promise based on whether any errors were encountered or not.

promise-all-wait.js

function reflect(obj) {
  if (!obj.then) {
    return { ok: true, value: obj };
  }

  return obj
  .then((value) => {
    return { ok: true, value };
  })
  .catch((err) => {
    return { ok: false, err };
  });
}

module.exports = function (promiseArr) {
  return Promise.all(promiseArr.map(reflect))
  .then((statuses) => {
    var error;
    var values = statuses.map((status) => {
      if (status.ok) {
        return status.value;
      }

      error = status.err;
    });

    if (error) {
      return Promise.reject(error);
    }

    return values;
  });
};