Loading "Intro to Cookies"

A bit of history

HTTP Cookies have been around since the very beginning of the web. They were invented to solve the problem of state management in web applications. Cookies allow websites to store small pieces of data on a user's device which is then sent along with every request to the server. This enables the server to maintain session information and remember user preferences across different interactions.
Cookies have become a fundamental part of web browsing and online user experiences, facilitating various functions such as session management, tracking user behavior, and personalization. However, due to privacy concerns, the use of cookies has evolved, and modern browsers provide users with more control over cookie settings, including options to block or delete cookies. Despite this, the most secure solution for managing user sessions is still to use cookies.


A common misconception among developers is that if your site uses cookies at all, it needs to display a GDPR banner. This is inaccurate. The topic of GDPR is complex and beyond the scope of this workshop (feel free to talk to a lawyer if you're concerned), but in general if you avoid the use of cookies for tracking and advertising purposes, you should be fine without a consent banner.
Learn more about how There is no EU Cookie Banner Law.

Cookies vs. Local Storage

Some applications store user information (like the user's ID or preferences) in localStorage. This is not a secure solution, as localStorage can be accessed by any script running on the page.
Additionally, localStorage is not sent with every request to the server, so the server cannot use it as part of the initial rendering of the page. This means that the page will not be able to display user-specific information until the client-side code has loaded and made a request to the server to retrieve the user's information.
Bad UX. Bad Security. Don't use it for this purpose.

How it works

First, the cookie needs to be set in the browser. This can happen on the client or on the server:
// Client-side
document.cookie = 'name=John Doe'
document.cookie is a string that contains all the cookies for the current domain. It's a funky API. You can definitely use it directly, but if you plan to work with cookies in the browser a lot, you may consider using a library like js-cookie.
Most of the time, you'll want to set the cookie on the server. This is because the server is the only place where you can securely set the cookie and you often want to set the cookie as part of the response to a request anyway.
// Server-side
const response = new Response(body, {
	headers: {
		'set-cookie': 'name=John Doe',
The API is a little less funky, but the string format is the same (and that is funky too), so a library to help parse and serialize cookie values can be helpful. A popular library for this is cookie.
When the browser receives the response, it will parse the set-cookie header and store the cookie in its "cookie jar". The browser will then send the cookie along with every request to the server.
Browsers can have multiple cookies each with its own name and configuration. We'll discuss this configuration more in the next exercise, but one important bit of configuration for this exercise is the path property. This determines which requests the cookie will be sent with. For example, if the cookie is set with a path of /admin, it will only be sent with requests to /admin and its subpaths (/admin/users, /admin/settings, etc.) but not for requests to / or /login.