Cache middleware pattern in Express - Mini Project: Build & Apply

Cache Middleware Pattern in Express

📖 Scenario: You are building a simple Express server that fetches user data. To speed up responses, you want to add a cache middleware that stores user data temporarily.

🎯 Goal: Create an Express middleware called cacheMiddleware that stores user data in a cache object. When a request comes in, the middleware should check if the user data is in the cache and return it immediately if found. Otherwise, it should let the request continue to fetch fresh data.

📋 What You'll Learn

Create a cache object to store user data keyed by user ID

Create a middleware function called cacheMiddleware

In the middleware, check if the requested user ID is in the cache

If cached data exists, send it as JSON response and do not call next()

If no cached data, call next() to continue to the route handler

In the route handler, fetch user data and store it in the cache

Send the user data as JSON response

💡 Why This Matters

🌍 Real World

Caching is used in web servers to speed up responses by storing frequently requested data temporarily.

💼 Career

Understanding middleware and caching is important for backend developers to build efficient and scalable web applications.

1

Create the cache object

Create an empty object called cache to store cached user data.

Express

import express from 'express';
const app = express();

app.use(express.json());

// Create an empty object called cache

app.listen(3000);

Need a hint?

Think of cache as a simple box where you keep user data for quick access.

2

Create the cache middleware

Create a middleware function called cacheMiddleware that takes req, res, and next as parameters.

Express

import express from 'express';
const app = express();

app.use(express.json());

const cache = {}

// Create cacheMiddleware function here

app.listen(3000);

Need a hint?

This function will check if data is in the cache before the route handler runs.

3

Add cache check logic in middleware

Inside cacheMiddleware, get userId from req.params. If cache[userId] exists, send it as JSON response and do not call next(). Otherwise, call next().

Express

import express from 'express';
const app = express();

app.use(express.json());

const cache = {}

function cacheMiddleware(req, res, next) {
  // Check cache for userId
  // Your code here
}

app.listen(3000);

Need a hint?

Use req.params.userId to find the user ID from the URL.

4

Use middleware and cache data in route

Add a GET route at /user/:userId that uses cacheMiddleware. In the route handler, create a userData object with id and name. Store userData in cache[userId] and send it as JSON response.

Express

import express from 'express';
const app = express();

app.use(express.json());

const cache = {}

function cacheMiddleware(req, res, next) {
  const userId = req.params.userId;
  if (cache[userId]) {
    res.json(cache[userId]);
  } else {
    next();
  }
}

// Add GET /user/:userId route using cacheMiddleware

app.listen(3000);

Need a hint?

This route uses the middleware to check cache before creating new user data.