Common memory leak patterns in Node.js - Mini Project: Build & Apply

Common Memory Leak Patterns in Node.js

📖 Scenario: You are building a simple Node.js application that processes user requests and stores session data temporarily. You want to understand common memory leak patterns so you can avoid them in your code.

🎯 Goal: Learn to identify and fix common memory leak patterns in Node.js by creating a small app that simulates these leaks and then applies fixes.

📋 What You'll Learn

Create an object to store session data

Add a configuration variable to limit session storage size

Implement a function to add sessions and simulate a memory leak

Fix the memory leak by removing old sessions

💡 Why This Matters

🌍 Real World

Web servers and applications often store user sessions or cache data in memory. Without limits, this can cause memory leaks and crash the server.

💼 Career

Understanding and fixing memory leaks is crucial for backend developers to build stable and scalable Node.js applications.

1

Create session storage object

Create an object called sessionStore to hold user session data. Initialize it as an empty object.

Node.js

// Create an object called sessionStore to hold session data
// Your code here

Need a hint?

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

2

Add session limit configuration

Add a constant called MAX_SESSIONS and set it to 100. This will limit how many sessions we keep in sessionStore.

Node.js

const sessionStore = {};
// Add a constant MAX_SESSIONS set to 100
// Your code here

Need a hint?

Use const MAX_SESSIONS = 100; to set the session limit.

3

Simulate memory leak by adding sessions

Write a function called addSession that takes sessionId and data. Add the data to sessionStore using sessionId as key. Do not remove old sessions yet, which causes a memory leak.

Node.js

const sessionStore = {};
const MAX_SESSIONS = 100;

// Write function addSession(sessionId, data) to add data to sessionStore
// Your code here

Need a hint?

Define function addSession(sessionId, data) and assign data to sessionStore[sessionId].

4

Fix memory leak by removing old sessions

Update addSession to check if sessionStore has more keys than MAX_SESSIONS. If yes, remove the oldest session key before adding the new one. Use Object.keys(sessionStore) to get keys and delete to remove a session.

Node.js

const sessionStore = {};
const MAX_SESSIONS = 100;

function addSession(sessionId, data) {
    // Fix memory leak by removing oldest session if limit exceeded
    // Your code here
}

Need a hint?

Check the number of keys with Object.keys(sessionStore).length. Remove the first key with delete sessionStore[oldestSession].