Cache invalidation strategies in Express - Mini Project: Build & Apply

Cache Invalidation Strategies in Express

📖 Scenario: You are building a simple Express server that caches user data to improve performance. However, cached data can become outdated. To keep the cache fresh, you need to implement cache invalidation strategies.

🎯 Goal: Build an Express server that caches user data in memory and invalidates the cache after a set time (time-based invalidation).

📋 What You'll Learn

Create an in-memory cache object to store user data

Add a cache expiration time variable

Implement a function to check and invalidate expired cache entries

Use middleware to serve cached data or fetch fresh data and update the cache

💡 Why This Matters

🌍 Real World

Caching is used in web servers to speed up responses by storing data temporarily. Cache invalidation keeps data fresh and prevents serving outdated information.

💼 Career

Understanding cache invalidation is important for backend developers to optimize performance and reliability of web applications.

1

Create the cache object

Create a variable called userCache and set it to an empty object {} to store cached user data.

Express

// Create a variable called userCache to store cached user data
// Your code here

Need a hint?

Use const userCache = {} to create an empty object for caching.

2

Add cache expiration time

Create a variable called cacheExpiration and set it to 60000 (milliseconds) to represent cache expiration time of 1 minute.

Express

const userCache = {};
// Create a variable called cacheExpiration and set it to 60000
// Your code here

Need a hint?

Set cacheExpiration to 60000 to represent 1 minute in milliseconds.

3

Implement cache invalidation function

Write a function called isCacheValid that takes a timestamp parameter and returns true if the current time minus timestamp is less than cacheExpiration, otherwise false.

Express

const userCache = {};
const cacheExpiration = 60000;
// Write function isCacheValid(timestamp) to check if cache is still valid
// Your code here

Need a hint?

Use Date.now() to get current time and compare with timestamp.

4

Use cache in Express route

In an Express GET route for /user/:id, check if userCache[id] exists and is valid using isCacheValid. If valid, send cached data. Otherwise, simulate fetching fresh data by creating an object with id and name as 'User ' + id, store it in userCache[id] with current timestamp, and send it.

Express

const userCache = {};
const cacheExpiration = 60000;

function isCacheValid(timestamp) {
    return (Date.now() - timestamp)  {
    const id = req.params.id;
    // Check cache and respond
    // Your code here
});

app.listen(3000);

Need a hint?

Check if cached data exists and is valid. If yes, send it. Otherwise, create fresh data, cache it with timestamp, and send it.