Web Storage

Web Storage lets a page save small string values in the browser for later use.

Two kinds of storage

localStorage

Data remains for the site until it is removed, even after the browser is closed.

sessionStorage

Data belongs to the current tab session and is removed when that session ends.

Basic example

localStorage.setItem('theme', 'dark');
const theme = localStorage.getItem('theme');
localStorage.removeItem('theme');

Storage values are strings. Convert JSON explicitly when you need to save an array or object, and handle unavailable storage or quota errors.

Security and privacy

• Do not store passwords, tokens, or other secrets in Web Storage.
• Any script running on the same origin may be able to read the values.
• Do not assume a value is valid just because it came from your own storage; validate it when reading.
• Provide a useful default when storage is disabled or cleared.