function parallel(fns, done) {
  let results = {};
  const callbaks = [];
  fns.forEach((fn, index) => {
    fn((result) => {
      results[index] = result;
      if (Object.keys(results).length === fns.length) {
        results = Object.keys(results).map((key) => results[key]);
        callbaks.forEach((cb) => {
          results = cb(results);
        });
      }
    });
  });
  
  const actions = {
    then: (cb) => {
      callbaks.push(cb);
      return actions;
    }
  };
  return actions;
}

function fn1(done) {
  setTimeout(function () {
    done('result a');
  }, 4000);
};

function fn2(done) {
  setTimeout(function () {
    done('result b');
  }, 2000);
};


parallel([fn1, fn2])
  .then((results) => results.map((r) => r + 'LOL'))
  .then((results) => console.log(results));

function fn1(done) {
  setTimeout(function () {
    done('result a');
  }, 4000);
};

function fn2(done) {
  setTimeout(function () {
    done('result b');
  }, 2000);
};


parallel([fn1, fn2])
  .then((results) => results.map((r) => r + 'LOL'))
  .then((results) => console.log(results));