YDoc

YDoc, often referred to as Y.Doc in code, is the central document model used by the Yjs library for building collaborative real-time applications. It represents a shared, editable document that can be modified by multiple clients concurrently. The document uses conflict-free replicated data type (CRDT) techniques to merge changes without requiring a central server.

Within a YDoc, data is organized into shared types such as maps, arrays, and text. These types support concurrent edits and automatically resolve conflicts when updates from different clients are applied. Yjs also provides specialized types for structured content, including variants used for more complex data structures.

State synchronization in YDoc is achieved through exchanging binary updates. Changes can be encoded as updates using functions that generate a Uint8Array, which can then be transmitted to other clients and applied to their YDocs with corresponding applyUpdate calls. State vectors can be used to enable incremental syncing, allowing clients to catch up efficiently by transmitting only the necessary changes since their last sync.

YDoc is typically used with network providers to connect clients, such as y-websocket or y-webrtc, and is often integrated with front-end frameworks to build collaborative editors, forms, or other real-time applications. It supports offline work, as local changes are reconciled when connectivity is restored, and provides mechanisms for undo and redo. The Yjs ecosystem emphasizes interoperability and extensibility, enabling developers to build complex collaborative experiences atop the YDoc core.