Request ID for tracing in Express - Mini Project: Build & Apply

Request ID for Tracing in Express

📖 Scenario: You are building a simple Express server that handles incoming requests. To help track each request uniquely, you want to add a request ID to every request. This ID will help you trace logs and debug issues easily.

🎯 Goal: Create an Express middleware that generates a unique request ID for each incoming request and attaches it to the request object. Then, use this ID in a route handler to send it back in the response.

📋 What You'll Learn

Create an Express app

Add middleware to generate a unique request ID using crypto.randomUUID()

Attach the request ID to req.id

Create a GET route at / that responds with the request ID in JSON format

💡 Why This Matters

🌍 Real World

Assigning unique request IDs helps developers trace and debug requests in logs, especially in complex or distributed systems.

💼 Career

Understanding middleware and request tracing is essential for backend developers working with Express or similar web frameworks.

1

Setup Express app

Create a variable called express by requiring the express module. Then create a variable called app by calling express().

Express

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

Need a hint?

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

2

Add request ID middleware

Create a middleware function that uses crypto.randomUUID() to generate a unique ID. Attach this ID to req.id. Use app.use() to add this middleware to the app. Remember to require crypto at the top.

Express

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

Need a hint?

Use app.use() to add a middleware that sets req.id to a new UUID.

3

Create GET route to return request ID

Add a GET route handler for path '/' using app.get(). In the handler, send a JSON response with a key requestId and value req.id.

Express

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

app.use((req, res, next) => {
    req.id = crypto.randomUUID();
    next();
});

// Your code here

Need a hint?

Use app.get() to create a route that sends back the request ID as JSON.

4

Start the server

Add code to start the Express server by calling app.listen() on port 3000. Provide a callback function that does nothing (empty arrow function).

Express

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

app.use((req, res, next) => {
    req.id = crypto.randomUUID();
    next();
});

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

// Your code here

Need a hint?

Use app.listen(3000, () => {}) to start the server on port 3000.