Request context middleware in Express - Mini Project: Build & Apply

Request Context Middleware in Express

📖 Scenario: You are building a simple Express server that needs to keep track of some information about each request, like a unique request ID and the time the request started. This helps in logging and debugging.

🎯 Goal: Create a middleware in Express that adds a requestContext object to each incoming request. This object should contain a unique requestId and a startTime. Then, use this context in a route to send back the request ID and start time.

📋 What You'll Learn

Create an Express app with a middleware function

Middleware adds a requestContext object to req

requestContext must have requestId as a unique string

requestContext must have startTime as the current timestamp

Create a GET route /info that returns JSON with requestId and startTime

💡 Why This Matters

🌍 Real World

Middleware like this is used in real web servers to track requests uniquely for logging, debugging, and performance monitoring.

💼 Career

Understanding request context middleware is important for backend developers working with Express or similar frameworks to build maintainable and debuggable web applications.

1

Setup Express app and import required modules

Write code to import express and create an Express app called app. Also, import crypto from Node.js to generate unique IDs.

Express

const express = require('express');
// Your code here

Need a hint?

Use require('express') to import Express and express() to create the app.

2

Create request context middleware

Create a middleware function called requestContextMiddleware that adds a requestContext object to req. This object should have a requestId generated by crypto.randomUUID() and startTime set to Date.now(). Use app.use(requestContextMiddleware) to apply it.

Express

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

// Create middleware to add requestContext
// Your code here

Need a hint?

Middleware functions take req, res, next. Add requestContext to req and call next().

3

Create GET /info route using request context

Add a GET route /info to app that sends a JSON response with requestId and startTime from req.requestContext.

Express

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

function requestContextMiddleware(req, res, next) {
    req.requestContext = {
        requestId: crypto.randomUUID(),
        startTime: Date.now()
    };
    next();
}

app.use(requestContextMiddleware);

// Add GET /info route here
// Your code here

Need a hint?

Use app.get with path /info. Send JSON with res.json() using values from req.requestContext.

4

Start the Express server

Add code to start the Express server on port 3000 using app.listen. Log a message Server running on port 3000 when it starts.

Express

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

function requestContextMiddleware(req, res, next) {
    req.requestContext = {
        requestId: crypto.randomUUID(),
        startTime: Date.now()
    };
    next();
}

app.use(requestContextMiddleware);

app.get('/info', (req, res) => {
    res.json({
        requestId: req.requestContext.requestId,
        startTime: req.requestContext.startTime
    });
});

// Start server on port 3000
// Your code here

Need a hint?

Use app.listen(3000, () => { ... }) to start the server and log the message.