Cookies, Sessions, and Cache

Cookies, Sessions, and Cache 

Cookies, Sessions, and Cache


Modern web applications rely on several client–server mechanisms to store data and improve performance. 

Among them, cookies, sessions, and cache are the most widely used. 

Although they can seem similar at first, each serves a different purpose. 


1. Cookies — Small Data Stored on the Client

Cookies are small text files stored in the user’s browser. 

They are sent with every request to the same domain, which makes them useful for remembering user information between visits.

1.1 What cookies are used for

  • Keeping users logged in

  • Saving site preferences (theme, language)

  • Tracking analytics and advertising

  • Shopping cart persistence


1.2 Characteristics

  • Stored on the client

  • Can persist for days, months, or years

  • Limited to around 4KB

  • Automatically included in HTTP requests


1.3 Example: Setting a cookie (JavaScript) 

document.cookie = "theme=dark; expires=Fri, 31 Dec 2026 23:59:59 GMT; path=/";

1.4 Example: Use case

A news website remembers the visitor’s preferred language (lang=en) so the user doesn’t need to pick it again.



2. Sessions — Server-Side Storage for User State

Sessions store data on the server, not the browser. They are used to keep track of a user’s state during a single visit or login period.

2.1 What sessions are used for

  • Authentication

  • Shopping cart during checkout

  • User-specific settings (server-side)

  • Sensitive data that should not be exposed to the client


2.2 Characteristics

  • Stored on the server

  • Identified by a session ID cookie

  • Automatically expires after inactivity

  • Much more secure than storing data directly in cookies


2.3 Example: Session flow

  1. User logs in

  2. Server creates a session → stores user ID

  3. Server sends a session_id cookie back

  4. Browser sends this session ID on each request

  5. Server retrieves the stored session data


2.4 Example (Express.js)

req.session.user = { id: 101, name: "Alice" };




3. Cache — Temporary Storage for Faster Loading

Cache stores static resources so the browser does not need to download them again. 

Unlike cookies and sessions, cache is mainly about performance, not state or identity.

3.1 What cache is used for

  • Images

  • CSS & JavaScript files

  • Fonts

  • API responses

  • Entire webpages (HTML)


3.2 Characteristics

  • Stored client-side (browser cache) or server-side (CDN)

  • Designed for speed and reducing bandwidth

  • Controlled by HTTP headers

  • Doesn’t store user identity


3.3 Example: Cache-Control header

Cache-Control: max-age=31536000, public


3.4 Example: Real usage

A blog’s logo is cached for 1 year to avoid downloading it on every visit.



4. Key Differences at a Glance


Feature Cookies Sessions Cache
Storage location Client browser Server Client / CDN
Purpose Identity,
preferences		 Authentication,
user state		 Performance
Size ~4KB Large (server memory/db) Varies (MBs)
Lifetime Set by expires/max-age Ends when session expires Controlled by cache headers
Security Lower, visible to user Higher, hidden from client Not related to user security
Automatically sent with request Yes Session ID only No



5. When to Use Cookies, Sessions, and Cache

5.1 Use Cookies when:

  • You need to remember a user between visits

  • Data is small and not sensitive

  • Example: darkMode=true, language preference, last-visited page


5.2 Use Sessions when:

  • Data is sensitive (user ID, permissions)

  • You need login state

  • Example: an e-commerce checkout or user profile page


5.3 Use Cache when:

  • You want faster loading

  • Resources rarely change

  • Example: images, fonts, JavaScript bundles




6. Real-World Example Scenario

Imagine a user logs into an online store.


6.1 Step 1 — Cookies

The site stores:

currency=USD
theme=light


6.2 Step 2 — Session

The server stores:

session.user = { id: 201, email: "abcdefg12345@example.com" }


6.3 Step 3 — Cache

The browser caches:

  • /styles.css

  • /script.js

  • Product images

When the user comes back tomorrow:

  • Cookies remember the theme & currency

  • Session expires so user logs in again

  • Cache loads images instantly

Each mechanism plays a different but essential role.



7. Conclusion

Although cookies, sessions, and cache all store data, they serve completely different purposes. 

Cookies remember user preferences, sessions manage authentication and state securely, and cache optimizes performance for a faster web experience. 

Understanding these differences helps you build efficient, secure, and user-friendly web applications.

Popular posts from this blog

The Early Search Engines: Yahoo, AltaVista, and the Dawn of Web Discovery

Image
The Early Search Engines: Yahoo, AltaVista, and the Dawn of Web Discovery When the World Wide Web first became public in the early 1990s, it was a chaotic digital landscape — thousands of pages scattered across servers around the world, with no easy way to find what you were looking for.  There were no smart algorithms, no Google, and no social media recommendations.  To explore the growing web, users needed a way to search it.  That’s where the first search engines came in.  Among them, Yahoo! and AltaVista were the pioneers that shaped how people discovered information online and laid the foundation for the search-dominated internet we use today. 1. The Problem of Finding Information on the Early Web In the early 1990s, the World Wide Web was growing rapidly.  What began as a small collection of research and university websites quickly expanded into thousands of public pages.  But unlike libraries, the web had no index or directory system.  Us...
Read more

The Birth of Internet Cafes and Online Communities

Image
The Birth of Internet Cafes and Online Communities The late 20th century marked a revolution in human communication.  The internet, once confined to research labs and universities, began spreading into homes, schools, and cities across the globe.  But before every household had Wi-Fi or smartphones, there was another space where people first experienced the digital world together — the Internet Cafe .  At the same time, online communities emerged, connecting people through shared interests, conversations, and digital friendships.  Together, these two phenomena laid the cultural and social foundation of the modern connected world. 1. The Rise of the Internet Cafe: A Gateway to the Digital World In the early 1990s, personal computers and internet connections were still expensive and not widely available.  For many, the first experience of going online didn’t happen at home but in a small, bustling space filled with computers — the Internet Cafe . The world’s ...
Read more

How Hyperlinks Changed the World

Image
How Hyperlinks Changed the World When we think about the internet, we often picture web pages, social media platforms, or search engines.  Yet, one of the most transformative inventions behind all of these is something so simple that we almost take it for granted: the hyperlink .  This seemingly small innovation—blue underlined text that connects one document to another—became the foundation of how we navigate the web.  It not only changed the way we access information but also reshaped communication, education, business, and even the way we think. 1. The Origins of the Hyperlink Idea The concept of linking information predates the modern web by several decades.  The first visionary to describe a system resembling hyperlinks was Vannevar Bush , an American engineer and science administrator.  In his 1945 essay “As We May Think” , Bush described a theoretical machine called the Memex , which would allow users to store books, records, and communications, and to...
Read more