Local Storage
What does local storage mean?
Local storage is a web browser feature that allows websites to store data persistently on a user’s device. Unlike cookies, which can expire or be deleted automatically, data saved in local storage remains indefinitely, until it is manually cleared by the user or deleted by the website’s code. This makes local storage particularly useful for storing information that needs to be retained across browsing sessions, such as user preferences, cached application data, or saved progress in a web app.
Because local storage operates entirely within the user’s browser, it provides a faster and more efficient way to store data locally without constantly sending it back and forth to a server. However, this same persistence means that developers must handle it carefully, especially when storing data that could be personal or sensitive.
How does local storage work?
Local storage uses the browser’s Web Storage API, a set of JavaScript methods that lets websites store and retrieve data in the form of key-value pairs. Each website can only access the data it created, due to the browser’s same-origin policy, which prevents one website from viewing another’s stored data.
Key characteristics of local storage include:
- Persistent data: Information stored in local storage remains available even after the browser or computer is restarted.
- Client-side only: Data is never automatically sent to servers with HTTP requests; it stays on the user’s device until specifically retrieved by JavaScript.
- Larger capacity: Local storage typically allows 5–10 MB per domain, compared to the 4 KB limit of cookies.
- Accessibility: Developers can easily set, read, and remove stored values using JavaScript commands such as
localStorage.setItem()orlocalStorage.getItem(). - Manual control: Users can delete stored data through their browser’s settings or when they clear cache and site data.
Common uses of local storage include:
- Saving user interface preferences like language, theme, or layout.
- Caching application data to improve speed and reduce server requests.
- Supporting offline access for progressive web apps (PWAs).
- Temporarily storing draft content such as form inputs or unsent messages.
Why is it important?
Local storage is valuable because it helps websites load faster, reduces dependence on servers, and improves user experience by retaining preferences between visits. It also enables modern web applications to function offline, providing a more app-like experience.
From a privacy perspective, however, its persistence creates potential risks. Since data stored locally can remain for months or years, it can be used to track users or store personal information without their awareness. For this reason, privacy regulations such as the GDPR and ePrivacy Directive treat certain uses of local storage the same way as cookies.
If local storage is used for non-essential purposes, such as tracking, analytics, or personalization, businesses must obtain valid user consent before saving data. Even when used for essential functions, its use should be documented and clearly described in a privacy or cookie notice.
FAQs about local storage
Yes, when used for non-essential or tracking purposes. For example, storing user behavior data or identifiers for analytics requires prior consent under GDPR. If it’s used only for functionality the user has requested, such as remembering a chosen language, it may be exempt.
Yes. Users can manually delete local storage through their browser’s settings, typically by clearing cache or site data. However, most users are unaware that this data persists, so it may remain indefinitely unless intentionally removed.
Not entirely. Because it’s accessible via JavaScript, local storage is vulnerable to cross-site scripting (XSS) attacks. Any malicious script running on the page can read or alter its contents. Sensitive data such as passwords, payment details, or tokens should never be stored there.
Cookies are smaller, automatically sent to the server with each request, and can have expiration dates. Local storage holds more data (up to 10 MB), never transmits automatically, and persists until deleted. While cookies are better suited for server-side sessions, local storage is designed for client-side web app data.
- Store only non-sensitive data.
- Avoid using it for long-term tracking or profiling.
- Clear outdated data regularly.
- Inform users about its purpose in your privacy or cookie notice.
- Combine with security controls to minimize XSS exposure.