app.js

// const express = require('express');
// const http = require('http');

// const app = express();

// const items = ['Di cho', 'Rua bat', 'Nau com'];

// const handleError = func => (req, res, next) => {
//   try {
//     func(req, res, next);
//   } catch (e) {
//     next(e);
//   }
// };

// const todoRouter = express.Router();

// todoRouter.get('/', (req, res, next) => {
//   res.send(items);
// });

// todoRouter.get('/:index', (req, res, next) => {
//   const index = parseInt(req.params.index);
//   if (!items[index]) {
//     const error = new Error('Todo item not found');
//     error.status = 404;
//     throw error;
//   }
//   res.send(items[index]);
// });

// todoRouter.get('/test/test', (req, res) => {
//   let i = 0;
//   const sendNext = () => {
//     setTimeout(() => {
//       res.write(`${i}`);
//       i++;
//       if (i < 10) {
//         sendNext();
//       } else {
//         res.end();
//       }
//     }, 1000);
//   };
//   sendNext();
// });

// app.use((req, res, next) => {
//   console.log(`${new Date().toString()} - ${req.method} - ${req.originalUrl}`);
//   next();
// });

// app.get('/divide/:a/:b', (req, res) => {
//   const a = parseFloat(req.params.a);
//   const b = parseFloat(req.params.b);

//   if (b === 0) {
//     throw new Error('Cannot divided by 0');
//   }

//   res.send(`${a} / ${b} = ${a / b}`);
// });

// app.get('/', (req, res) => res.send('Hello!'));
// app.use('/todos', todoRouter);

// app.use((err, req, res, next) => {
//   if (err) {
//     res.status(err.status || 500);
//     res.send(`${err.status || 500} - ${err.message}`);
//   } else {
//     next();
//   }
// });

// http.createServer(app).listen(3000, () => console.log(`Server started.`));

// const mongoose = require('mongoose');
// mongoose.connect('mongodb://localhost/test-async');

// const Item = mongoose.model(
//   'item',
//   {
//     title: String
//   },
//   'items'
// );

const items = [];

const save = (title, cb) => {
  setTimeout(() => {
    const item = {
      title,
      id: items.length
    };
    items.push(item);
    cb(null, item);
  }, Math.random() * 100);
};

const names = ['di cho', 'rua bat', 'nau com'];

const forEach = (arr, func, done) => {
  let completed = 0;
  let results = [];
  for (let i = 0; i < arr.length; i++) {
    const item = arr[i];
    func(item, (err, result) => {
      results[i] = result;
      completed++;
      if (completed >= arr.length) {
        done(null, results);
      }
    });
  }
};

const forEachSeries = (arr, func, done) => {
  let results = [];
  const runCurrent = current => {
    if (current >= arr.length) {
      done(null, results);
      return;
    }
    let item = arr[current];
    func(item, (err, result) => {
      if (err) {
        done(err);
        return;
      }
      results[current] = result;
      runCurrent(current + 1);
    });
  };
  runCurrent(0);
};

forEachSeries(
  names,
  (name, cb) => {
    save(name, (err, item) => {
      console.log(item);
      cb(err, item);
    });
  },
  (err, items) => console.log(items)
);