IndexedDB
IndexedDB is a low-level, asynchronous browser API for storing significant amounts of structured data — including files and blobs — on the client, with support for indexes, transactions, and querying.
Definition
IndexedDB is a low-level, asynchronous browser API for storing significant amounts of structured data — including files and blobs — on the client, with support for indexes, transactions, and querying.
Overview
IndexedDB is a full transactional, object-oriented database built into modern browsers. Unlike Local Storage, which is limited to small string key-value pairs accessed synchronously, IndexedDB stores structured JavaScript objects (including nested data and binary blobs) in indexed object stores, and all operations are asynchronous so they don't block the main thread — a critical difference for larger datasets. Data is organized into named 'object stores' within a database, each of which can define indexes on specific properties to enable efficient querying beyond simple key lookups. Reads and writes happen within transactions, which guarantee consistency even if multiple operations are happening concurrently. Because the raw API is verbose and callback- or event-based, many developers use wrapper libraries (such as Dexie.js or idb) to interact with it through a friendlier promise-based interface. IndexedDB is a foundational building block for offline-capable web applications: paired with a Service Worker intercepting network requests, it allows an app to cache substantial amounts of data and function usefully without a network connection, then sync back up once connectivity returns. Storage limits are much larger than local storage — often hundreds of megabytes or more, subject to browser-specific quota management — making it suitable for caching datasets, offline document editors, and local-first applications. Heavy read/write workloads against IndexedDB are sometimes moved into a Web Worker to keep the main thread free for rendering, and it is a common storage layer behind client-side state persisted by libraries like Zustand.
Key Concepts
- Asynchronous, non-blocking API suited for larger amounts of data
- Stores structured objects and binary data, not just strings
- Supports indexes for efficient querying beyond simple key lookups
- Transactional reads and writes ensure data consistency
- Much higher storage capacity than local storage, often hundreds of MB or more
- Foundational for offline-first web applications alongside service workers
- Often wrapped by friendlier libraries like Dexie.js or idb due to its verbose native API