localStorage & State Management — Free JavaScript Tutorial

TL;DR: Learn localStorage & State Management in JavaScript with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

localStorage & State Management in JavaScript

localStorage allows JavaScript apps to persist data between sessions. Data survives tab close and browser restart. sessionStorage is similar but data is lost when tab closes.

Both have the same API: setItem(key, value), getItem(key), removeItem(key), clear(). Values are always strings — use JSON.stringify and JSON.parse for objects.

Custom events and state management patterns keep the UI in sync with stored data. When data changes, update both localStorage and the DOM.

Common patterns: auto-save (store on every input event), hydration (load from localStorage on page start), undo/redo (store history array).

// Save (always stringify objects)
localStorage.setItem('user', JSON.stringify({ name: 'Priya', score: 92 }));

// Load (always parse objects)
const user = JSON.parse(localStorage.getItem('user') || '{}');

// Check if exists
if (localStorage.getItem('user')) { ... }

// Clear all
localStorage.clear();

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