demo.js

// const each = (arr, iterator, cb) => {
//   const results = [];
//   let done = 0;
//   let hasError = false;
//   for (let i = 0; i < arr.length; i++) {
//     const item = arr[i];

//     iterator(item, (err, result) => {
//       if (hasError) return;
//       if (err) {
//         cb(err);
//         hasError = true;
//         return;
//       }
//       results[i] = result;
//       done++;
//       if (done == arr.length) {
//         cb(null, results);
//       }
//     });
//   }
// };

// const eachSeries = (arr, iterator, cb) => {
//   const results = [];
//   let hasError = false;
//   let index = 0;
//   const cloneArr = arr;
//   const next = () => {
//     iterator(arr[index], (err, result) => {
//       if (hasError) return;
//       if (err) {
//         cb(err);
//         hasError = true;
//         return;
//       }

//       if (result != undefined) {
//         results.push(result);
//       }

//       if (index < arr.length - 1) {
//         index++;
//         next();
//       } else {
//         cb(null, results);
//       }
//     });
//   };
//   next(cloneArr, iterator, cb);
// };

// const getAccountIds = (userId, cb) => {
//   setTimeout(() => cb(null, [1, 2, 3]), 100);
// };

// const getAccountDetail = (accountId, cb) => {
//   setTimeout(() => cb(null, `Detail of account ${accountId}`), 1000);
// };

// const getAccountDetails = (userId, cb) => {
//   getAccountIds(userId, (err, accountIds) => {
//     if (err) {
//       return cb(err);
//     }
//     eachSeries(
//       accountIds,
//       (accountId, cb) => {
//         console.log(`Processing ${accountId}`);
//         getAccountDetail(accountId, cb);
//       },
//       cb
//     );
//   });
// };

// getAccountDetails(1, (err, details) => console.log(err, details));

// function* getId() {
//   let i = 0;
//   while (true) {
//     yield i++;
//   }
// }

// const idGenerator = getId();
// console.log(idGenerator.next().value);
// console.log(idGenerator.next().value);
// console.log(idGenerator.next().value);
// console.log(idGenerator.next().value);
// console.log(idGenerator.next().value);
// console.log(idGenerator.next().value);
// console.log(idGenerator.next().value);

const co = genFunc => {
  
};

const getAccountIds = userId => {
  return new Promise((resolve, reject) => {
    setTimeout(() => resolve([1, 2, 3]), 100);
  });
};

const getAccountDetail = accountId => {
  return new Promise(resolve =>
    setTimeout(() => cb(null, `Detail of account ${accountId}`), 100)
  );
};

getAccountIds(1).then(ids => console.log(ids)).catch(err => console.log(err));

co(function*() {
  const ids = yield getAccountIds(1);
  const details = [];
  for (let id of ids) {
    const detail = yield getAccountDetail(id);
    details.push(detail);
  }
  console.log(details);
});