Local Storage vs Cookies

Cookies and local storage serve different purposes. Cookies are primarily for reading server-side, local storage can only be read by the client-side. So the question is, in your app, who needs this data — the client or the server?

If it's your client (your JavaScript), then by all means switch. You're wasting bandwidth by sending all the data in each HTTP header.

If it's your server, local storage isn't so useful because you'd have to forward the data along somehow (with Ajax or hidden form fields or something). This might be okay if the server only needs a small subset of the total data for each request.

You'll want to leave your session cookie as a cookie either way though.

As per the technical difference, and also my understanding:

Apart from being an old way of saving data, Cookies give you a limit of 4096 bytes (4095, actually) — it's per cookie. Local Storage is as big as 5MB per domain — SO Question also mentions it. localStorage is an implementation of the Storage Interface. It stores data with no expiration date, and gets cleared only through JavaScript, or clearing the Browser Cache / Locally Stored Data — unlike cookie expiry.

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In the context of JWTs, Stormpath have written a fairly helpful article outlining possible ways to store them, and the (dis-)advantages pertaining to each method.

It also has a short overview of XSS and CSRF attacks, and how you can combat them.

I've attached some short snippets of the article below, in case their article is taken offline/their site goes down.

Local Storage

Problems:

Web Storage (localStorage/sessionStorage) is accessible through JavaScript on the same domain. This means that any JavaScript running on your site will have access to web storage, and because of this can be vulnerable to cross-site scripting (XSS) attacks. XSS in a nutshell is a type of vulnerability where an attacker can inject JavaScript that will run on your page. Basic XSS attacks attempt to inject JavaScript through form inputs, where the attacker puts alert('You are Hacked'); into a form to see if it is run by the browser and can be viewed by other users.

Prevention:

To prevent XSS, the common response is to escape and encode all untrusted data. But this is far from the full story. In 2015, modern web apps use JavaScript hosted on CDNs or outside infrastructure. Modern web apps include 3rd party JavaScript libraries for A/B testing, funnel/market analysis, and ads. We use package managers like Bower to import other peoples’ code into our apps. What if only one of the scripts you use is compromised? Malicious JavaScript can be embedded on the page, and Web Storage is compromised. These types of XSS attacks can get everyone’s Web Storage that visits your site, without their knowledge. This is probably why a bunch of organizations advise not to store anything of value or trust any information in web storage. This includes session identifiers and tokens. As a storage mechanism, Web Storage does not enforce any secure standards during transfer. Whoever reads Web Storage and uses it must do their due diligence to ensure they always send the JWT over HTTPS and never HTTP.

Cookies

Problems:

Cookies, when used with the HttpOnly cookie flag, are not accessible through JavaScript, and are immune to XSS. You can also set the Secure cookie flag to guarantee the cookie is only sent over HTTPS. This is one of the main reasons that cookies have been leveraged in the past to store tokens or session data. Modern developers are hesitant to use cookies because they traditionally required state to be stored on the server, thus breaking RESTful best practices. Cookies as a storage mechanism do not require state to be stored on the server if you are storing a JWT in the cookie. This is because the JWT encapsulates everything the server needs to serve the request. However, cookies are vulnerable to a different type of attack: cross-site request forgery (CSRF). A CSRF attack is a type of attack that occurs when a malicious web site, email, or blog causes a user’s web browser to perform an unwanted action on a trusted site on which the user is currently authenticated. This is an exploit of how the browser handles cookies. A cookie can only be sent to the domains in which it is allowed. By default, this is the domain that originally set the cookie. The cookie will be sent for a request regardless of whether you are on galaxies.com or hahagonnahackyou.com.

Prevention:

Modern browsers support the SameSite flag, in addition to HttpOnly and Secure. The purpose of this flag is to prevent the cookie from being transmitted in cross-site requests, preventing many kinds of CSRF attack. For browsers that do not support SameSite, CSRF can be prevented by using synchronized token patterns. This sounds complicated, but all modern web frameworks have support for this. For example, AngularJS has a solution to validate that the cookie is accessible by only your domain. Straight from AngularJS docs: When performing XHR requests, the $http service reads a token from a cookie (by default, XSRF-TOKEN) and sets it as an HTTP header (X-XSRF-TOKEN). Since only JavaScript that runs on your domain can read the cookie, your server can be assured that the XHR came from JavaScript running on your domain. You can make this CSRF protection stateless by including a xsrfToken JWT claim: { "iss": "http://galaxies.com", "exp": 1300819380, "scopes": ["explorer", "solar-harvester", "seller"], "sub": "tom@andromeda.com", "xsrfToken": "d9b9714c-7ac0-42e0-8696-2dae95dbc33e" } Leveraging your web app framework’s CSRF protection makes cookies rock solid for storing a JWT. CSRF can also be partially prevented by checking the HTTP Referer and Origin header from your API. CSRF attacks will have Referer and Origin headers that are unrelated to your application.

The full article can be found here: https://stormpath.com/blog/where-to-store-your-jwts-cookies-vs-html5-web-storage/

They also have a helpful article on how to best design and implement JWTs, with regards to the structure of the token itself: https://stormpath.com/blog/jwt-the-right-way/

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With localStorage, web applications can store data locally within the user's browser. Before HTML5, application data had to be stored in cookies, included in every server request. Large amounts of data can be stored locally, without affecting website performance. Although localStorage is more modern, there are some pros and cons to both techniques.

Cookies

Pros

Legacy support (it's been around forever)

Persistent data

Expiration dates

Cookies can be marked as HTTPOnly which might limit XSS atacks to user browser during his sesion (does not guarantee full immunity to XSS atacks).

Cons

Each domain stores all its cookies in a single string, which can make parsing data difficult

Data is unencrypted, which becomes an issue because... ... though small in size, cookies are sent with every HTTP request Limited size (4KB)

Local storage

Pros

Support by most modern browsers

Persistent data that is stored directly in the browser

Same-origin rules apply to local storage data

Is not sent with every HTTP request

~5MB storage per domain (that's 5120KB)

Cons

Not supported by anything before: IE 8, Firefox 3.5, Safari 4, Chrome 4, Opera 10.5, iOS 2.0, Android 2.0

If the server needs stored client information you purposely have to send it.

localStorage usage is almost identical with the session one. They have pretty much exact methods, so switching from session to localStorage is really child's play. However, if stored data is really crucial for your application, you will probably use cookies as a backup in case localStorage is not available. If you want to check browser support for localStorage, all you have to do is run this simple script:

/* 
* function body that test if storage is available
* returns true if localStorage is available and false if it's not
*/
function lsTest(){
    var test = 'test';
    try {
        localStorage.setItem(test, test);
        localStorage.removeItem(test);
        return true;
    } catch(e) {
        return false;
    }
}

/* 
* execute Test and run our custom script 
*/
if(lsTest()) {
    // window.sessionStorage.setItem(name, 1); // session and storage methods are very similar
    window.localStorage.setItem(name, 1);
    console.log('localStorage where used'); // log
} else {
    document.cookie="name=1; expires=Mon, 28 Mar 2016 12:00:00 UTC";
    console.log('Cookie where used'); // log
}

"localStorage values on Secure (SSL) pages are isolated" as someone noticed keep in mind that localStorage will not be available if you switch from 'http' to 'https' secured protocol, where the cookie will still be accesible. This is kind of important to be aware of if you work with secure protocols.

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Cookies:

Introduced prior to HTML5. Has expiration date. Cleared by JS or by Clear Browsing Data of browser or after expiration date. Will sent to the server per each request. The capacity is 4KB. Only strings are able to store in cookies. There are two types of cookies: persistent and session.

Local Storage:

Introduced with HTML5. Does not have expiration date. Cleared by JS or by Clear Browsing Data of the browser. You can select when the data must be sent to the server. The capacity is 5MB. Data is stored indefinitely, and must be a string. Only have one type.

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It is also worth mentioning that localStorage cannot be used when users browse in "private" mode in some versions of mobile Safari.

Quoted from WayBack Archive of MDN topic on Window.localStorage back in 2018:

Note: Starting with iOS 5.1, Safari Mobile stores localStorage data in the cache folder, which is subject to occasional clean up, at the behest of the OS, typically if space is short. Safari Mobile's Private Browsing mode also prevents writing to localStorage entirely.

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Key Differences:

Capacity:

Local Storage: 10MB

Cookies: 4kb

Browser Support:

Local Storage: HTML5

Cookies: HTML4, HTML5

Storage Location:

Local Storage: Browser Only

Cookies: Browser & Server

Send With Request:

Local Storage: Yes

Cookies: No

Accessed From:

Local Storage: Any Window

Cookies: Any Window.

Expiry Date:

Local Storage: Never Expire, until done by javascript.

Cookies: Yes, Have expiry date.

Note: Use that, what suits you.

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Well, local storage speed greatly depends on the browser the client is using, as well as the operating system. Chrome or Safari on a mac could be much faster than Firefox on a PC, especially with newer APIs. As always though, testing is your friend (I could not find any benchmarks).

I really don't see a huge difference in cookie vs local storage. Also, you should be more worried about compatibility issues: not all browsers have even begun to support the new HTML5 APIs, so cookies would be your best bet for speed and compatibility.

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Local storage can store up to 5mb offline data, whereas session can also store up to 5 mb data. But cookies can store only 4kb data in text format.

LOCAl and Session storage data in JSON format, thus easy to parse. But cookies data is in string format.

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Cookie:

is accessible by JavaScript so Cookie's data can be stolen by XSS attack(Cross Site Scripting attack) but setting HttpOnly flag to Cookie prevents the access by JavaScript so Cookie's data is protected from XSS attack.

is vulnerable to CSRF(Cross Site Request Forgery) but setting SameSite flag with Lax to Cookie mitigates CSRF and setting SameSite flag with Strict to Cookie prevents CSRF.

must have expiry date so when expiry date passes, Cookie is deleted automatically so even if you forgot to delete Cookie, Cookie is deleted automatically because of expiry date.

is about 4KB as a common size (depending on browsers).

Local Storage:

is accessible by JavaScript so Local Storage's data can be stolen by XSS attack(Cross Site Scripting attack) then, as logn as I researched, there are no easy preventions for Local Storage from XSS attack.

is not vulnerable to CSRF(Cross Site Request Forgery).

doesn't have expiry date so if you forgot to delete Local Storage data, Local Storage data can stay forever.

is about 5MB as a common size (depending on browsers).

I recommend using Cookie for sensitive data and Local Storage for non-sensitive data.

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