IndexedDB

IndexedDB is a low-level API for client-side storage of significant amounts of structured data, including files and blobs. It provides a transactional, index-enabled database system in the browser, allowing web applications to store and retrieve objects with keys and to search them efficiently via indexes.

Data is stored in object stores inside a database. Each object store holds records as key-value pairs, with a primary key that can be provided or auto-incremented. Object stores can have one or more indexes to support efficient queries. Data is stored using the structured clone algorithm, enabling objects, arrays, and binary data to be stored.

All operations occur within transactions, which can be readonly or readwrite. IndexedDB is asynchronous; operations return requests that fire success or error events. You open a database with indexedDB.open(name, version); onupgradeneeded is invoked when a new version is created, in which you create object stores and indexes. Queries include get, put, add, delete, openCursor, and getAll.

IndexedDB provides ACID-like properties per transaction. Data modifications are atomic within a transaction, and changes persist according to the origin's storage quotas. The API is supported by modern browsers (Chrome, Firefox, Safari, Edge). It uses the browser's storage, not cookies, and does not support SQL joins; use indexes to query.

Common use cases include offline-first web apps, caching of large datasets, and client-side storage for multimedia or JSON data. Limitations include API complexity, asynchronous programming requirements, potential performance considerations for large datasets, and reliance on per-origin storage quotas and user permissions for persistent storage.