Why middleware is Express's core concept - See It in Action

Understanding Middleware in Express

📖 Scenario: You are building a simple web server using Express. Middleware functions are the building blocks that handle requests and responses step-by-step, like a team passing a message along a chain.

🎯 Goal: Build a basic Express server that uses middleware to log requests, check a condition, and send a response.

📋 What You'll Learn

Create an Express app variable

Add a middleware function to log each request's method and URL

Add a middleware function to check if a query parameter allow equals true

Send a response with Access granted if allowed, otherwise Access denied

💡 Why This Matters

🌍 Real World

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

💼 Career

Understanding middleware is essential for backend developers working with Express or similar web frameworks to build scalable and maintainable web applications.

1

Set up Express app

Create a variable called express by requiring the 'express' module, then create a variable called app by calling express().

Express

# Your code here

Need a hint?

Use require('express') to import Express and then call it as a function to create the app.

2

Add logging middleware

Add a middleware function to app using app.use that logs the HTTP method and URL of each request using console.log. Use parameters req, res, and next. Call next() at the end.

Express

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

// Your code here

Need a hint?

Middleware functions take three arguments and must call next() to pass control.

3

Add access control middleware

Add another middleware function to app using app.use that checks if req.query.allow equals the string 'true'. If yes, call next() to continue. Otherwise, send a response with Access denied and do not call next().

Express

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

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

// Your code here

Need a hint?

Check the query parameter and decide whether to continue or send a response.

4

Add final response handler

Add a middleware function to app using app.use that sends the response Access granted. This will run only if previous middleware called next().

Express

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

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

app.use((req, res, next) => {
    if (req.query.allow === 'true') {
        next();
    } else {
        res.send('Access denied');
    }
});

// Your code here

Need a hint?

This middleware sends the final response if access is allowed.