Async middleware wrapper in Express - Mini Project: Build & Apply

Async Middleware Wrapper in Express

📖 Scenario: You are building a simple Express server. You want to handle errors in asynchronous middleware functions easily without repeating try-catch blocks.

🎯 Goal: Create an async middleware wrapper function that catches errors from async route handlers and passes them to Express error handling.

📋 What You'll Learn

Create an async middleware wrapper function called asyncWrapper

Use asyncWrapper to wrap an async route handler

The wrapper should catch errors and call next(error)

Set up a basic Express server with one async route using the wrapper

💡 Why This Matters

🌍 Real World

Async middleware wrappers help keep Express route handlers clean and handle errors consistently without repeating try-catch blocks.

💼 Career

Understanding async error handling in Express is essential for backend developers building reliable Node.js web applications.

1

Setup Express server and async route handler

Create an Express app by requiring express and calling express(). Then create an async route handler function called getData that returns a resolved promise with the string 'Hello World'.

Express

const express = require('express');
const app = express();

// Create async route handler function getData
// Your code here

Need a hint?

Use async function getData(req, res) and return a string inside.

2

Create async middleware wrapper function

Create a function called asyncWrapper that takes a function fn as argument and returns a new function with parameters req, res, next. Inside, call fn(req, res, next) and catch any error to call next(error).

Express

const express = require('express');
const app = express();

async function getData(req, res) {
    return 'Hello World';
}

// Create asyncWrapper function
// Your code here

Need a hint?

Return a function that calls fn and catches errors with Promise.resolve(...).catch(next).

3

Use asyncWrapper to wrap async route handler

Use app.get to create a GET route at '/'. Pass asyncWrapper(getData) as the route handler. Inside getData, send the string 'Hello World' as the response using res.send().

Express

const express = require('express');
const app = express();

async function getData(req, res) {
    return 'Hello World';
}

function asyncWrapper(fn) {
    return function(req, res, next) {
        Promise.resolve(fn(req, res, next)).catch(next);
    };
}

// Use asyncWrapper to wrap getData in app.get
// Your code here

Need a hint?

Wrap getData with asyncWrapper in app.get and use res.send inside getData.

4

Add error handling middleware and start server

Add an error handling middleware with four parameters err, req, res, next that sends status 500 and the error message. Then start the server on port 3000 using app.listen.

Express

const express = require('express');
const app = express();

async function getData(req, res) {
    res.send('Hello World');
}

function asyncWrapper(fn) {
    return function(req, res, next) {
        Promise.resolve(fn(req, res, next)).catch(next);
    };
}

app.get('/', asyncWrapper(getData));

// Add error handling middleware and start server
// Your code here

Need a hint?

Use app.use with four parameters for error handling and app.listen(3000) to start the server.