Why caching matters in Node.js - See It in Action

Why caching matters

📖 Scenario: You are building a simple Node.js server that fetches user data from a slow database. To make the server faster and reduce repeated database calls, you will add caching.

🎯 Goal: Build a Node.js server that caches user data in memory to avoid repeated slow database calls.

📋 What You'll Learn

Create a function to simulate fetching user data from a slow database

Create a cache object to store user data

Add logic to check the cache before fetching from the database

Return cached data if available, otherwise fetch and cache it

💡 Why This Matters

🌍 Real World

Caching is used in web servers to speed up responses by storing data temporarily, reducing slow database calls.

💼 Career

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

1

Create a function to simulate slow database fetch

Create a function called fetchUserFromDB that takes a userId parameter and returns a Promise that resolves to an object { id: userId, name: 'User' + userId } after 100 milliseconds.

Node.js

// Create the fetchUserFromDB function that simulates slow database fetch
// Your code here

Need a hint?

Use setTimeout inside a Promise to simulate delay.

2

Create a cache object

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

Node.js

function fetchUserFromDB(userId) {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve({ id: userId, name: 'User' + userId });
        }, 100);
    });
}

// Create cache object here
// Your code here

Need a hint?

Use a plain object to store cached data by userId keys.

3

Add caching logic to fetch user data

Create an async function called getUser that takes userId. Inside, check if cache[userId] exists. If yes, return it. Otherwise, call fetchUserFromDB(userId), store the result in cache[userId], then return it.

Node.js

function fetchUserFromDB(userId) {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve({ id: userId, name: 'User' + userId });
        }, 100);
    });
}

const cache = {};

// Create async function getUser with caching logic
// Your code here

Need a hint?

Use async/await and check the cache before fetching.

4

Export the getUser function

Add module.exports = { getUser }; at the end to export the getUser function for use in other files.

Node.js

function fetchUserFromDB(userId) {
    return new Promise(resolve => {
        setTimeout(() => {
            resolve({ id: userId, name: 'User' + userId });
        }, 100);
    });
}

const cache = {};

async function getUser(userId) {
    if (cache[userId]) {
        return cache[userId];
    }
    const user = await fetchUserFromDB(userId);
    cache[userId] = user;
    return user;
}

// Export getUser function
// Your code here

Need a hint?

Use module.exports to export the function.