In-memory caching patterns in Node.js - Mini Project: Build & Apply

In-memory caching patterns in Node.js

📖 Scenario: You are building a simple Node.js app that fetches user data from a slow database. To speed up repeated requests, you want to store user data temporarily in memory.

🎯 Goal: Build a basic in-memory cache using a JavaScript object to store user data keyed by user ID. Implement cache lookup, cache insertion, and cache expiration logic.

📋 What You'll Learn

Create an object called cache to hold cached user data

Create a variable called cacheDuration set to 30000 (milliseconds)

Write a function getUserFromCache that returns cached data if not expired

Write a function setUserInCache that stores user data with a timestamp

Add logic to check cache expiration before returning cached data

💡 Why This Matters

🌍 Real World

In-memory caching is used in web servers to speed up repeated data requests and reduce database load.

💼 Career

Understanding caching patterns is important for backend developers to improve application performance and scalability.

1

Create the cache storage object

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

Node.js

// Create an empty object called cache
// Your code here

Need a hint?

Use const cache = {} to create an empty object.

2

Set cache duration time

Create a variable called cacheDuration and set it to 30000 milliseconds (30 seconds).

Node.js

const cache = {}
// Create cacheDuration variable and set to 30000
// Your code here

Need a hint?

Use const cacheDuration = 30000; to set the cache time.

3

Write function to get user from cache

Write a function called getUserFromCache that takes userId as a parameter. It should check if cache[userId] exists and if the cached timestamp is within cacheDuration. Return the cached data if valid, otherwise return null.

Node.js

const cache = {};
const cacheDuration = 30000;

// Write getUserFromCache function
// Your code here

Need a hint?

Check if cache[userId] exists and if Date.now() - cached.timestamp < cacheDuration. Return cached data or null.

4

Write function to set user in cache

Write a function called setUserInCache that takes userId and userData as parameters. It should store an object in cache[userId] with data set to userData and timestamp set to the current time using Date.now().

Node.js

const cache = {};
const cacheDuration = 30000;

function getUserFromCache(userId) {
    const cached = cache[userId];
    if (cached) {
        const isValid = (Date.now() - cached.timestamp) < cacheDuration;
        if (isValid) {
            return cached.data;
        }
    }
    return null;
}

// Write setUserInCache function
// Your code here

Need a hint?

Store an object with data and timestamp in cache[userId].