Middleware concept and execution flow in Node.js - Mini Project: Build & Apply

Middleware Concept and Execution Flow in Node.js

📖 Scenario: You are building a simple Node.js server that handles requests step-by-step using middleware functions. Middleware are like helpers that process requests one after another, like a line of workers passing a package along.

🎯 Goal: Build a Node.js server using Express that demonstrates how middleware functions run in order and modify the request and response objects.

📋 What You'll Learn

Create an Express app with a basic route

Add two middleware functions that modify the request object

Modify the route handler to send a response using the modified request data

Understand the order of middleware execution and how next() controls flow

💡 Why This Matters

🌍 Real World

Middleware is used in real web servers to handle authentication, logging, data parsing, and more, all in a clean, step-by-step way.

💼 Career

Understanding middleware is essential for backend developers working with Node.js and Express, as it is a core pattern for building scalable web applications.

1

Set up Express app and initial route

Create a variable called express that requires the 'express' module. Then create a variable called app by calling express(). Finally, add a GET route on '/' that takes req, res and sends the text 'Hello' as the response.

Node.js

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

// Your code here

Need a hint?

Use require('express') to import Express. Then call express() to create the app. Use app.get to add a route.

2

Add first middleware to add a property to request

Add a middleware function using app.use that takes req, res, and next. Inside it, add a property req.firstName with the value 'Alice'. Then call next() to pass control to the next middleware.

Node.js

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

app.use((req, res, next) => {
  // Your code here
});

app.get('/', (req, res) => {
  res.send('Hello');
});

Need a hint?

Middleware functions get req, res, and next. Add the property to req and call next().

3

Add second middleware to add lastName to request

Add another middleware function using app.use that takes req, res, and next. Inside it, add a property req.lastName with the value 'Smith'. Then call next() to continue the flow.

Node.js

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

app.use((req, res, next) => {
  req.firstName = 'Alice';
  next();
});

app.use((req, res, next) => {
  // Your code here
});

app.get('/', (req, res) => {
  res.send('Hello');
});

Need a hint?

Just like the first middleware, add req.lastName and call next().

4

Modify route to send full name using middleware data

Change the GET route on '/' so that it sends a response with the text `Hello ${req.firstName} ${req.lastName}` using template literals. This shows how middleware data is used in the final response.

Node.js

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

app.use((req, res, next) => {
  req.firstName = 'Alice';
  next();
});

app.use((req, res, next) => {
  req.lastName = 'Smith';
  next();
});

app.get('/', (req, res) => {
  // Your code here
});

Need a hint?

Use template literals with backticks to include req.firstName and req.lastName in the response.