Async error handling in routes in Express - Mini Project: Build & Apply

Async Error Handling in Express Routes

📖 Scenario: You are building a simple Express server that fetches user data asynchronously. You want to handle errors properly in your routes so the server does not crash and sends meaningful error messages to clients.

🎯 Goal: Create an Express route that fetches user data asynchronously and handles errors using async/await and try/catch blocks.

📋 What You'll Learn

Create an Express app with a route /user/:id

Use an async function to simulate fetching user data

Add a configuration variable for a delay time

Use try/catch inside the route to handle errors

Send a JSON response with user data or error message

💡 Why This Matters

🌍 Real World

Handling asynchronous operations and errors in web server routes is essential for building reliable APIs that do not crash and provide clear feedback to clients.

💼 Career

Backend developers frequently write async routes in Express and must handle errors properly to maintain server stability and good user experience.

1

Set up Express app and user data

Create a variable called express that requires the 'express' module. Then create an Express app by calling express() and assign it to a variable called app. Finally, create a constant object called users with these exact entries: 1: { name: 'Alice' }, 2: { name: 'Bob' }.

Express

# Your code here

Need a hint?

Use require('express') to import Express. Create app by calling express(). Define users as an object with keys 1 and 2.

2

Add delay configuration variable

Create a constant called delay and set it to 1000 (milliseconds).

Express

const express = require('express');
const app = express();
const users = {
  1: { name: 'Alice' },
  2: { name: 'Bob' }
};

// Your code here

Need a hint?

Just create a constant delay and assign it the number 1000.

3

Create async function to fetch user data

Write an async function called getUserById that takes id as a parameter. Inside, return a new Promise that waits for delay milliseconds using setTimeout. After the delay, if users[id] exists, resolve with users[id], otherwise reject with an Error with message 'User not found'.

Express

const express = require('express');
const app = express();
const users = {
  1: { name: 'Alice' },
  2: { name: 'Bob' }
};

const delay = 1000;

// Your code here

Need a hint?

Use new Promise with setTimeout to simulate delay. Resolve if user exists, reject with error if not.

4

Add async route with error handling

Add a GET route to app at path /user/:id. Use an async function with parameters req and res. Inside, use a try/catch block. In try, await getUserById(req.params.id) and send the user data as JSON with res.json(user). In catch, send a 404 status with JSON containing { error: error.message }.

Express

const express = require('express');
const app = express();
const users = {
  1: { name: 'Alice' },
  2: { name: 'Bob' }
};

const delay = 1000;

async function getUserById(id) {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      if (users[id]) {
        resolve(users[id]);
      } else {
        reject(new Error('User not found'));
      }
    }, delay);
  });
}

// Your code here

Need a hint?

Use app.get with async function. Use try/catch to await getUserById. Send JSON response or error with status 404.