Middleware ordering matters in Node.js - Mini Project: Build & Apply

Middleware ordering matters

📖 Scenario: You are building a simple Node.js server using Express. Middleware functions are like helpers that run in order when a request comes in. The order you add them matters because each middleware can change the request or response, or stop the chain.

🎯 Goal: Build an Express server with two middleware functions and one route handler. Learn how changing the order of middleware affects the server's behavior.

📋 What You'll Learn

Create an Express app

Add a middleware that adds a requestTime property to req

Add a middleware that logs the request method and URL

Add a route handler for GET / that sends back the request time

Understand how changing middleware order changes the output

💡 Why This Matters

🌍 Real World

Middleware ordering is important in real web servers to control authentication, logging, data parsing, and error handling in the right sequence.

💼 Career

Understanding middleware order is key for backend developers working with Node.js and Express to build reliable and maintainable web applications.

1

Create Express app and first middleware

Create an Express app by requiring express and calling express(). Then add a middleware using app.use that adds a requestTime property to the req object with the current date and time as a string.

Node.js

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

// Your code here

Need a hint?

Use app.use to add middleware. Inside, set req.requestTime to new Date().toISOString() and call next().

2

Add logging middleware

Add a second middleware using app.use that logs the HTTP method and URL of each request using console.log. Use req.method and req.url. Then call next() to continue.

Node.js

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

app.use((req, res, next) => {
    req.requestTime = new Date().toISOString();
    next();
});

// Your code here

Need a hint?

Use app.use again to add the logging middleware. Use template strings to log method and URL.

3

Add route handler for GET /

Add a route handler for GET requests to / using app.get. The handler should send a response with the text: Request time: followed by the requestTime property from req.

Node.js

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

app.use((req, res, next) => {
    req.requestTime = new Date().toISOString();
    next();
});

app.use((req, res, next) => {
    console.log(`${req.method} ${req.url}`);
    next();
});

// Your code here

Need a hint?

Use app.get with path '/'. Send the request time using res.send and template strings.

4

Add server listen and test middleware order

Add app.listen to start the server on port 3000. Then explain how switching the order of the two app.use middleware calls changes whether the log shows before or after the requestTime is set.

Node.js

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

app.use((req, res, next) => {
    req.requestTime = new Date().toISOString();
    next();
});

app.use((req, res, next) => {
    console.log(`${req.method} ${req.url}`);
    next();
});

app.get('/', (req, res) => {
    res.send(`Request time: ${req.requestTime}`);
});

// Your code here

Need a hint?

Use app.listen(3000) to start the server. Try moving the logging middleware before the requestTime middleware to see how the log changes.