localStorage and sessionStorage

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Browser Storage

localStorage persists data across browser sessions (until cleared). sessionStorage clears when the tab is closed. Both store only strings, so serialize complex data with JSON.stringify.

javascript

// Write
localStorage.setItem("username", "Alice");
localStorage.setItem("prefs", JSON.stringify({ theme: "dark", lang: "en" }));

// Read
const name  = localStorage.getItem("username"); // "Alice"
const prefs = JSON.parse(localStorage.getItem("prefs"));

// Check for key
localStorage.getItem("missing"); // null

// Delete
localStorage.removeItem("username");

// Clear everything
localStorage.clear();

// sessionStorage has the same API but tab-scoped
sessionStorage.setItem("cart", JSON.stringify([]));

Never store sensitive data (passwords, tokens, personal info) in localStorage — it is accessible to any script on the page, making it vulnerable to XSS attacks. Use HttpOnly cookies for auth tokens.

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