repository·master·Indexed 27 days ago
https://github.com/share/sharedbShareDB is a realtime JSON OT (Operational Transformation) database backend enabling multi-user collaboration and real-time synchronization. It supports various database adapters (MemoryDB, MongoDB, PostgreSQL), pub/sub integrations for horizontal scaling, and milestone adapters for document history snapshots. The API provides a Backend class for managing client connections, middleware registration, and document operations across browser and server environments.
ShareDB is a full-stack library designed for real-time JSON document collaboration. It consists of two main components:
Conflict management is handled via Operational Transformation (OT), with specific strategies implemented through ShareDB's type plugins.
ShareDB uses database adapters to persist document contents and operations (ops). Choose an adapter based on your persistence and query requirements:
sharedb-mongo): Backed by MongoDB. Provides full query support.sharedb-mingo-memory): An in-memory database that implements a subset of MongoDB operations, including queries. Useful for testing against a MongoDB-like environment.sharedb-postgres): Backed by PostgreSQL. It has no query support.ShareDB provides the following capabilities for building collaborative applications:
ShareDB delegates the implementation of operational transformation to OT types. To use a custom OT type, you must register it on both the server and the client.
Note: Failure to register the type on both sides will result in errors when attempting to synchronize operations.
// Server-side registration
const Backend = require('sharedb')
const richText = require('rich-text')
Backend.types.register(richText.type)
// Client-side registration
const Client = require('sharedb/lib/client')
const richText = require('rich-text')
Client.types.register(richText.type)LocalPresence instance represents the local client's presence (e.g., a cursor position or a highlighted field) and is created from a parent Presence instance using the presence.create() method.json0 as its default Operational Transformation (OT) type. If you do not explicitly specify a type when calling doc.create(), the document will be initialized using json0.Install ShareDB using npm. If your server and client are in separate packages, you must add sharedb as a dependency to both the server and client packages.
npm install --save sharedbYou can use untyped presence to share transient information (like mouse coordinates) independently of a specific document.
connection.getPresence(channel) to get a Presence instance and call .subscribe().'receive' event. An update of null indicates the remote client is no longer present.LocalPresence instance via presence.create() and call .submit(value). The value can be any arbitrary shape.Note: You can create multiple LocalPresence instances from a single Presence instance to represent multiple cursors or inputs.
const presence = connection.getPresence('my-channel')
presence.subscribe()
presence.on('receive', (presenceId, update) => {
if (update === null) {
// The remote client is no longer present in the document
} else {
// Handle the new value by updating UI, etc.
}
})
const localPresence = presence.create()
// The presence value can take any shape
localPresence.submit({foo: 'bar'})To couple presence to a specific document and ensure synchronization with document operations (preventing issues like cursor jitter), use DocPresence.
connection.getDocPresence(collection, id) to get a DocPresence instance and call .subscribe().'receive' event. An update of null indicates the remote client is no longer present.LocalPresence via presence.create() and call .submit(value). The shape of the value is determined by the document type.Note: Currently, only the rich-text type supports presence information.
const presence = connection.getDocPresence(collection, id)
presence.subscribe()
presence.on('receive', (presenceId, update) => {
if (update === null) {
// The remote client is no longer present in the document
} else {
// Handle the new value by updating UI, etc.
}
})
const localPresence = presence.create()
// The presence value depends on the type
localPresence.submit(value)To use a database adapter, instantiate the adapter and pass it to the db option in the Backend constructor.
const backend = new Backend({
db: new MemoryDB(),
})