Practice: Express Routing, Async/Await & Mini REST API

Let's think about it this way for a moment

This lesson is meant to combine the knowledge from Express Intro, Express Routing, Async & Promises, and API Intro/GET/POST into broader hands-on practice. Each task builds on the last, using route parameters, async functions, and an in-memory array as the data store, and you'll write out an entire CRUD flow yourself. Testing your logic this carefully before hooking up a database in a real project makes connecting a database later much easier. Send requests for each task through Postman or the browser and confirm the results.

Exercises

Task 1: Build an Express app and return the in-memory array 'books' (id, title, author) via a GET /books route. Task 2: Add a GET /books/:id route that returns a 404 status with an error message if no book matches the id. Task 3: Create a POST /books route using the express.json() middleware, and push a new book from the request body into the array — make the id auto-increment. Task 4: Write a delay() helper function that wraps setTimeout in a Promise, and use async/await to add a 500ms delay in the GET /books/:id route to simulate 'searching a database'.

• Can extract the Express route parameter (:id) with req.params and write filter/find logic
• Can use the express.json() middleware to parse a POST request body
• Can correctly use async/await with a Promise-wrapped delay function inside a route handler

Code Example

const express = require('express');
const app = express();
app.use(express.json());

let books = [
  { id: 1, title: 'Node.js Basics', author: 'Aung' },
  { id: 2, title: 'Express Guide', author: 'Su' }
];

const delay = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

// Task 1
app.get('/books', (req, res) => {
  res.json(books);
});

// Task 2 + 4: param + async delay
app.get('/books/:id', async (req, res) => {
  await delay(500); // simulate database lookup
  const book = books.find((b) => b.id === Number(req.params.id));
  if (!book) {
    return res.status(404).json({ error: 'Book not found' });
  }
  res.json(book);
});

// Task 3
app.post('/books', (req, res) => {
  const { title, author } = req.body;
  if (!title || !author) {
    return res.status(400).json({ error: 'title and author required' });
  }
  const newBook = { id: books.length + 1, title, author };
  books.push(newBook);
  res.status(201).json(newBook);
});

app.listen(3000, () => console.log('API running on port 3000'));

GET /books returns the book list as a JSON array; GET /books/:id waits 500ms before returning a single book (or a 404); and POST /books adds a new book to the array when you send a body.