What is IndexedDB?

Every major browser ships with a built-in database called IndexedDB. Unlike cookies (tiny, simple key-value pairs capped at 4KB) or localStorage (string-only key-value store capped at 5–10MB), IndexedDB is a full NoSQL document database that can store structured JavaScript objects, binary blobs, arrays, and typed data. Quotas vary by browser and disk space, but modern browsers typically allow IndexedDB to use several hundred megabytes to gigabytes per origin. This makes it the right tool for storing thousands of user records, cached API responses, or exported datasets locally in the browser.

How IndexedDB Works

IndexedDB is organized into databases, each containing multiple object stores (analogous to tables in SQL). Each record in an object store has a key (auto-generated or specified) and a value (any JavaScript object). You can create indexes on any property of stored objects to enable fast lookups without scanning every record. All reads and writes happen within transactions, which provide atomicity — either all operations in a transaction succeed, or none do, preventing partial writes that could corrupt data. The API is asynchronous and callback-based (though libraries like Dexie.js wrap it in a modern Promise/async interface).

IndexedDB in Browser Extensions

Browser extensions use IndexedDB extensively for storing large local datasets. An extension that collects your followers from a social media platform across multiple paginated requests needs somewhere to accumulate those records before generating a CSV export. chrome.storage.local (limited to about 10MB by default) is too small for a user with 50,000 followers. IndexedDB has no such hard cap — it can store the full dataset locally while the collection process runs, then read it all back out when generating the export file. This local-first architecture means your data never leaves your browser during collection, providing a meaningful privacy benefit.

Comparison with Other Browser Storage Options

Choosing the right browser storage depends on data size and structure. Cookies (4KB max) are suited for session tokens. localStorage (5–10MB, synchronous) is convenient for small settings and preferences. chrome.storage.local (10MB default, up to 5MB per item) is the right choice for extension settings and small datasets because it syncs with the Chrome extension APIs. IndexedDB wins for large, structured datasets that need querying, sorting, or pagination — think thousands of records with multiple queryable fields. The Cache API is designed specifically for caching network responses for offline use and is typically used alongside service workers in PWAs rather than extensions.

Privacy Benefits of Local Storage

A key advantage of IndexedDB for privacy-focused extensions is that data stored in IndexedDB stays entirely in the user's browser. No server receives the data, no account is required, and no cloud sync occurs. The data is stored on disk in the browser's profile directory, protected by the OS user account. This zero-knowledge approach to data handling — where the extension developer literally cannot access the stored data because it never leaves the device — is a meaningful privacy guarantee for tools that handle social graph information or browsing-related data.