PouchDB

PouchDB is an open-source JavaScript database inspired by Apache CouchDB, designed to run within the browser and enable web developers to build applications that work as well offline as they do online. Now an Apache Software Foundation project at version 9.0.0, the library is lightweight at just 46 kilobytes gzipped and is installed via npm or a single script tag. Data is persisted locally using IndexedDB in modern browsers, WebSQL as a fallback, and LevelDB in Node.js environments. The core innovation is bidirectional replication with CouchDB and compatible servers, which synchronizes local data when the application regains connectivity, ensuring the user data stays in sync across devices and sessions. The API mirrors CouchDB, providing document storage with JSON attachments, MapReduce views, design documents, conflict resolution via deterministic revision trees, and the changes feed for real-time event-driven synchronization. The database works across Firefox, Chrome, Opera, Safari, Internet Explorer, and Node.js with identical behavior. PouchDB Server provides a standalone CouchDB-compatible HTTP API server for development and testing. Framework integrations include React PouchDB, Ember Pouch, PouchDB Angular, and Vue Pouch, with adapter plugins for custom storage backends. The project maintains extensive documentation including guides for replication strategies, conflict handling, performance optimization, and migration from IndexedDB-only implementations. Major community contributions include PouchDB Find for Mango query syntax and PouchDB Authentication for cookie-based session management.