JavaScript - Promise Map

promiseMap.js

// https://codesandbox.io/s/promisemap-o7f7n

const getData = id =>
  new Promise((res, rej) => {
    setTimeout(() => {
      const data = { id, uid: (Math.random() * 100).toFixed(2) };
      console.log("data", data);
      res(data);
    }, 100);
  });

function promiseMap(inputValues, mapper) {
  const reducer = (acc$, inputValue, index) =>
    acc$.then(acc =>
      mapper(inputValue, index).then(result => acc.push(result) && acc)
    );
  return inputValues.reduce(reducer, Promise.resolve([]));
}

const ids = [1, 5, 3, 4, 9];

promiseMap(ids, id => {
  const start = new Date();
  console.log();
  console.log("Loading... ", id);
  // return a Promise
  return getData(id).then(data => {
    const end = new Date();
    const time = end - start;
    console.log(`Loaded in ${time} secs`, data);
    // return some data
    return data;
  });
}).then(values => {
  console.log("\n---\n");
  console.info("All values:");
  values.forEach(item => console.log(item));
});