localStorage and sessionStorage

Syntax

localStorage.setItem(key, value)
localStorage.getItem(key)

Examples

localStorage.setItem("username", "alice");
console.log(localStorage.getItem("username")); // "alice"

localStorage.removeItem("username");
console.log(localStorage.getItem("username")); // null

localStorage.setItem("theme", "dark");
localStorage.setItem("fontSize", "16");
localStorage.clear(); // removes everything

const userPrefs = { theme: "dark", fontSize: 16, notifications: true };

localStorage.setItem("preferences", JSON.stringify(userPrefs));

const stored = JSON.parse(localStorage.getItem("preferences"));
console.log(stored.theme); // "dark"
console.log(typeof stored); // "object" - properly restored, not just a string

// Persists across browser restarts, until explicitly cleared
localStorage.setItem("rememberedEmail", "user@example.com");

// Cleared automatically when the tab/browser is closed
sessionStorage.setItem("currentStep", "3");

// Both share the identical API - only the lifetime differs

Best practices

• Always wrap JSON.parse() calls on stored data in a try/catch, in case the stored value is missing or corrupted
• Use sessionStorage for temporary, per-tab data (like a multi-step form's progress), and localStorage for data that should persist long-term
• Never store sensitive information (passwords, tokens, personal data) in localStorage - it is accessible to any JavaScript running on the page, including malicious scripts
• Remember storage is per-origin (protocol + domain + port) and has a size limit (typically around 5-10MB) - it is not a substitute for a real database

At a glance

Purpose

Application logic and interaction

File extension

.js · .mjs

Runs in

Browsers and JavaScript runtimes

Usually used with

HTML, CSS and Web APIs

Specifications & further reading

• ECMAScript specification

Related JavaScript documentation