When localStorage's string limit isn't enough, IndexedDB stores large amounts of structured data (objects, blobs) with indexes and transactions — fully async. The raw API is verbose (open a database, version it, create object stores, run transactions), so most apps use a wrapper like idb. It powers offline apps and big client-side caches.
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<body style="background:#06040d;color:#e6e0ff;font-family:monospace;padding:20px"><pre>const req = indexedDB.open('app', 1);
req.onupgradeneeded = e => e.target.result.createObjectStore('todos', { keyPath: 'id' });
req.onsuccess = e => {
const db = e.target.result;
db.transaction('todos','readwrite').objectStore('todos').add({ id:1, text:'learn idb' });
};</pre></body></html>