The web is stateless. LocalStorage allows us to persist user preferences (like Dark Mode) between visits.
JSON: The Universal Language
javascript
const data = { id: 1, title: "Learn JS" };
// Object -> String (Packing)
const packed = JSON.stringify(data);
console.log(packed); // '{"id":1,"title":"Learn JS"}'
// String -> Object (Unpacking)
const unpacked = JSON.parse(packed);
console.log(unpacked.title);Security Warning
NEVER store sensitive data
LocalStorage is accessible by any JavaScript running on your page (including analytics scripts or browser extensions).
NEVER store passwords, credit card info, or sensitive API tokens in LocalStorage. Use HttpOnly Cookies for that.
Using LocalStorage
javascript
// It only stores Strings!
localStorage.setItem("score", "100");
// Convert back to number when reading
const score = parseInt(localStorage.getItem("score"));
console.log(score + 50); // 150