![Yjs](https://yjs.dev/images/logo/yjs-120x120.png)
A CRDT framework with a powerful abstraction of shared data
Yjs is a CRDT implementation that exposes its internal
data structure as shared types. Shared types are common data types like Map
or Array
with superpowers: changes are automatically distributed to other
peers and merged without merge conflicts.
Yjs is network agnostic (p2p!), supports many existing rich text
editors, offline editing, version snapshots, undo/redo and
shared cursors. It scales well with an unlimited number of users and is well
suited for even large documents.
:construction_worker_woman: If you are looking for professional support, please
consider supporting this project via a "support contract" on
GitHub Sponsors. I will attend your issues
quicker and we can discuss questions and problems in regular video conferences.
Otherwise you can find help on our community discussion board.
Please contribute to the project financially - especially if your company relies
on Yjs. ![Become a Sponsor](https://img.shields.io/static/v1?label=Become%20a%20Sponsor&message=%E2%9D%A4&logo=GitHub&style=flat&color=d42f2d)
Professional Support
- Support Contract with the Maintainer -
By contributing financially to the open-source Yjs project, you can receive
professional support directly from the author. This includes the opportunity for
weekly video calls to discuss your specific challenges.
- Synergy Codes - Specializing in
consulting and developing real-time collaborative editing solutions for visual
apps, Synergy Codes focuses on interactive diagrams, complex graphs, charts, and
various data visualization types. Their expertise empowers developers to build
engaging and interactive visual experiences leveraging the power of Yjs. See
their work in action at Visual Collaboration
Showcase.
Who is using Yjs
- AFFiNE A local-first, privacy-first, open source
knowledge base. 🏅
- Cargo Site builder for designers and artists :star2:
- Gitbook Knowledge management for technical teams :star2:
- Evernote Note-taking app :star2:
- Lessonspace Enterprise platform for virtual
classrooms and online training :star2:
- Dynaboard Build web apps collaboratively. :star:
- Relm A collaborative gameworld for teamwork and
community. :star:
- Room.sh A meeting application with integrated
collaborative drawing, editing, and coding tools. :star:
- Nimbus Note A note-taking app designed by
Nimbus Web. :star:
- Pluxbox RadioManager A web-based app to
collaboratively organize radio broadcasts. :star:
- Sana A learning platform with collaborative text
editing powered by Yjs.
- Serenity Notes End-to-end encrypted
collaborative notes app.
- PRSM Collaborative mind-mapping and system visualisation. (source)
- Alldone A next-gen project management and
collaboration platform.
- Living Spec A modern way for product teams to collaborate.
- Slidebeamer Presentation app.
- BlockSurvey End-to-end encryption for your forms/surveys.
- Skiff Private, decentralized workspace.
- JupyterLab Collaborative computational Notebooks
- JupyterCad Extension to
JupyterLab that enables collaborative editing of 3d FreeCAD Models.
- Hyperquery A collaborative data workspace for
sharing analyses, documentation, spreadsheets, and dashboards.
- Nosgestesclimat The french carbon
footprint calculator has a group P2P mode based on yjs
- oorja.io Online meeting spaces extensible with
collaborative apps, end-to-end encrypted.
- LegendKeeper Collaborative campaign planner and
worldbuilding app for tabletop RPGs.
- IllumiDesk Build courses and content with A.I.
- btw Open-source Medium alternative
- AWS SageMaker Tools for building Machine
Learning Models
- linear Streamline issues, projects, and product roadmaps.
Table of Contents
Overview
This repository contains a collection of shared types that can be observed for
changes and manipulated concurrently. Network functionality and two-way-bindings
are implemented in separate modules.
Bindings
Providers
Setting up the communication between clients, managing awareness information,
and storing shared data for offline usage is quite a hassle. Providers
manage all that for you and are the perfect starting point for your
collaborative app.
This list of providers is incomplete. Please open PRs to add your providers to
this list!
Connection Providers
- y-websocket
-
A module that contains a simple websocket backend and a websocket client that
connects to that backend. The backend can be extended to persist updates in a
leveldb database. y-sweet and ypy-websocket (see below) are
compatible to the y-wesocket protocol.
- y-webrtc
-
Propagates document updates peer-to-peer using WebRTC. The peers exchange
signaling data over signaling servers. Publically available signaling servers
are available. Communication over the signaling servers can be encrypted by
providing a shared secret, keeping the connection information and the shared
document private.
- @liveblocks/yjs
-
Liveblocks Yjs provides a fully
hosted WebSocket infrastructure and persisted data store for Yjs
documents. No configuration or maintenance is required. It also features
Yjs webhook events, REST API to read and update Yjs documents, and a
browser DevTools extension.
- y-sweet
-
A standalone yjs server with persistence to S3 or filesystem. They offer a
cloud service as well.
- PartyKit
-
Cloud service for building multiplayer apps.
- y-libp2p
-
Uses libp2p to propagate updates via
GossipSub.
Also includes a peer-sync mechanism to catch up on missed updates.
- y-dat
-
[WIP] Write document updates efficiently to the dat network using
multifeed. Each client has
an append-only log of CRDT local updates (hypercore). Multifeed manages and sync
hypercores and y-dat listens to changes and applies them to the Yjs document.
- Matrix-CRDT
-
Use Matrix as an off-the-shelf backend for
Yjs by using the MatrixProvider.
Use Matrix as transport and storage of Yjs updates, so you can focus building
your client app and Matrix can provide powerful features like Authentication,
Authorization, Federation, hosting (self-hosting or SaaS) and even End-to-End
Encryption (E2EE).
- yrb-actioncable
-
An ActionCable companion for Yjs clients. There is a fitting
redis extension as well.
- ypy-websocket
-
Websocket backend, written in Python.
Persistence Providers
- y-indexeddb
-
Efficiently persists document updates to the browsers indexeddb database.
The document is immediately available and only diffs need to be synced through the
network provider.
- y-mongodb-provider
-
Adds persistent storage to a server with MongoDB. Can be used with the
y-websocket provider.
-
@toeverything/y-indexeddb
-
Like y-indexeddb, but with sub-documents support and fully TypeScript.
Ports
There are several Yjs-compatible ports to other programming languages.
- y-octo - Rust implementation by
AFFiNE
- y-crdt - Rust implementation with multiple
language bindings to other languages
- ycs - .Net compatible C# implementation.
Getting Started
Install Yjs and a provider with your favorite package manager:
npm i yjs y-websocket
Start the y-websocket server:
PORT=1234 node ./node_modules/y-websocket/bin/server.js
Example: Observe types
import * as Y from 'yjs';
const doc = new Y.Doc();
const yarray = doc.getArray('my-array')
yarray.observe(event => {
console.log('yarray was modified')
})
yarray.insert(0, ['val'])
Example: Nest types
Remember, shared types are just plain old data types. The only limitation is
that a shared type must exist only once in the shared document.
const ymap = doc.getMap('map')
const foodArray = new Y.Array()
foodArray.insert(0, ['apple', 'banana'])
ymap.set('food', foodArray)
ymap.get('food') === foodArray
ymap.set('fruit', foodArray)
Now you understand how types are defined on a shared document. Next you can jump
to the demo repository or continue reading
the API docs.
Example: Using and combining providers
Any of the Yjs providers can be combined with each other. So you can sync data
over different network technologies.
In most cases you want to use a network provider (like y-websocket or y-webrtc)
in combination with a persistence provider (y-indexeddb in the browser).
Persistence allows you to load the document faster and to persist data that is
created while offline.
For the sake of this demo we combine two different network providers with a
persistence provider.
import * as Y from 'yjs'
import { WebrtcProvider } from 'y-webrtc'
import { WebsocketProvider } from 'y-websocket'
import { IndexeddbPersistence } from 'y-indexeddb'
const ydoc = new Y.Doc()
const indexeddbProvider = new IndexeddbPersistence('count-demo', ydoc)
indexeddbProvider.whenSynced.then(() => {
console.log('loaded data from indexed db')
})
const webrtcProvider = new WebrtcProvider('count-demo', ydoc)
const websocketProvider = new WebsocketProvider(
'wss://demos.yjs.dev', 'count-demo', ydoc
)
const yarray = ydoc.getArray('count')
yarray.observe(event => {
console.log('new sum: ' + yarray.toArray().reduce((a,b) => a + b))
})
yarray.push([1])
API
import * as Y from 'yjs'
Shared Types
Y.Array
A shareable Array-like type that supports efficient insert/delete of elements
at any position. Internally it uses a linked list of Arrays that is split when
necessary.
const yarray = new Y.Array()
parent:Y.AbstractType|null
insert(index:number, content:Array<object|boolean|Array|string|number|null|Uint8Array|Y.Type>)
-
Insert content at index. Note that content is an array of elements.
I.e.
array.insert(0, [1])
splices the list and inserts 1 at
position 0.
push(Array<Object|boolean|Array|string|number|null|Uint8Array|Y.Type>)
unshift(Array<Object|boolean|Array|string|number|null|Uint8Array|Y.Type>)
delete(index:number, length:number)
get(index:number)
slice(start:number, end:number):Array<Object|boolean|Array|string|number|null|Uint8Array|Y.Type>
- Retrieve a range of content
length:number
forEach(function(value:object|boolean|Array|string|number|null|Uint8Array|Y.Type,
index:number, array: Y.Array))
map(function(T, number, YArray):M):Array<M>
toArray():Array<object|boolean|Array|string|number|null|Uint8Array|Y.Type>
- Copies the content of this YArray to a new Array.
toJSON():Array<Object|boolean|Array|string|number|null>
-
Copies the content of this YArray to a new Array. It transforms all child types
to JSON using their
toJSON
method.
[Symbol.Iterator]
-
Returns an YArray Iterator that contains the values for each index in the array.
for (let value of yarray) { .. }
observe(function(YArrayEvent, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type is modified. In the case this type is modified in the event listener,
the event listener will be called again after the current event listener returns.
unobserve(function(YArrayEvent, Transaction):void)
-
Removes an
observe
event listener from this type.
observeDeep(function(Array<YEvent>, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type or any of its children is modified. In the case this type is modified
in the event listener, the event listener will be called again after the current
event listener returns. The event listener receives all Events created by itself
or any of its children.
unobserveDeep(function(Array<YEvent>, Transaction):void)
-
Removes an
observeDeep
event listener from this type.
Y.Map
A shareable Map type.
const ymap = new Y.Map()
parent:Y.AbstractType|null
size: number
- Total number of key/value pairs.
get(key:string):object|boolean|string|number|null|Uint8Array|Y.Type
set(key:string, value:object|boolean|string|number|null|Uint8Array|Y.Type)
delete(key:string)
has(key:string):boolean
get(index:number)
clear()
- Removes all elements from this YMap.
clone():Y.Map
- Clone this type into a fresh Yjs type.
toJSON():Object<string, Object|boolean|Array|string|number|null|Uint8Array>
-
Copies the
[key,value]
pairs of this YMap to a new Object.It
transforms all child types to JSON using their toJSON
method.
forEach(function(value:object|boolean|Array|string|number|null|Uint8Array|Y.Type,
key:string, map: Y.Map))
-
Execute the provided function once for every key-value pair.
[Symbol.Iterator]
-
Returns an Iterator of
[key, value]
pairs.
for (let [key, value] of ymap) { .. }
entries()
-
Returns an Iterator of
[key, value]
pairs.
values()
-
Returns an Iterator of all values.
keys()
-
Returns an Iterator of all keys.
observe(function(YMapEvent, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type is modified. In the case this type is modified in the event listener,
the event listener will be called again after the current event listener returns.
unobserve(function(YMapEvent, Transaction):void)
-
Removes an
observe
event listener from this type.
observeDeep(function(Array<YEvent>, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type or any of its children is modified. In the case this type is modified
in the event listener, the event listener will be called again after the current
event listener returns. The event listener receives all Events created by itself
or any of its children.
unobserveDeep(function(Array<YEvent>, Transaction):void)
-
Removes an
observeDeep
event listener from this type.
Y.Text
A shareable type that is optimized for shared editing on text. It allows to
assign properties to ranges in the text. This makes it possible to implement
rich-text bindings to this type.
This type can also be transformed to the
delta format. Similarly the
YTextEvents compute changes as deltas.
const ytext = new Y.Text()
parent:Y.AbstractType|null
insert(index:number, content:string, [formattingAttributes:Object<string,string>])
-
Insert a string at index and assign formatting attributes to it.
ytext.insert(0, 'bold text', { bold: true })
delete(index:number, length:number)
format(index:number, length:number, formattingAttributes:Object<string,string>)
- Assign formatting attributes to a range in the text
applyDelta(delta: Delta, opts:Object<string,any>)
-
See Quill Delta
Can set options for preventing remove ending newLines, default is true.
ytext.applyDelta(delta, { sanitize: false })
length:number
toString():string
- Transforms this type, without formatting options, into a string.
toJSON():string
- See
toString
toDelta():Delta
-
Transforms this type to a Quill Delta
observe(function(YTextEvent, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type is modified. In the case this type is modified in the event listener,
the event listener will be called again after the current event listener returns.
unobserve(function(YTextEvent, Transaction):void)
-
Removes an
observe
event listener from this type.
observeDeep(function(Array<YEvent>, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type or any of its children is modified. In the case this type is modified
in the event listener, the event listener will be called again after the current
event listener returns. The event listener receives all Events created by itself
or any of its children.
unobserveDeep(function(Array<YEvent>, Transaction):void)
-
Removes an
observeDeep
event listener from this type.
Y.XmlFragment
A container that holds an Array of Y.XmlElements.
const yxml = new Y.XmlFragment()
parent:Y.AbstractType|null
firstChild:Y.XmlElement|Y.XmlText|null
insert(index:number, content:Array<Y.XmlElement|Y.XmlText>)
delete(index:number, length:number)
get(index:number)
slice(start:number, end:number):Array<Y.XmlElement|Y.XmlText>
- Retrieve a range of content
length:number
clone():Y.XmlFragment
- Clone this type into a fresh Yjs type.
toArray():Array<Y.XmlElement|Y.XmlText>
- Copies the children to a new Array.
toDOM():DocumentFragment
- Transforms this type and all children to new DOM elements.
toString():string
- Get the XML serialization of all descendants.
toJSON():string
- See
toString
.
createTreeWalker(filter: function(AbstractType<any>):boolean):Iterable
- Create an Iterable that walks through the children.
observe(function(YXmlEvent, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type is modified. In the case this type is modified in the event listener,
the event listener will be called again after the current event listener returns.
unobserve(function(YXmlEvent, Transaction):void)
-
Removes an
observe
event listener from this type.
observeDeep(function(Array<YEvent>, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type or any of its children is modified. In the case this type is modified
in the event listener, the event listener will be called again after the current
event listener returns. The event listener receives all Events created by itself
or any of its children.
unobserveDeep(function(Array<YEvent>, Transaction):void)
-
Removes an
observeDeep
event listener from this type.
Y.XmlElement
A shareable type that represents an XML Element. It has a nodeName
,
attributes, and a list of children. But it makes no effort to validate its
content and be actually XML compliant.
const yxml = new Y.XmlElement()
parent:Y.AbstractType|null
firstChild:Y.XmlElement|Y.XmlText|null
nextSibling:Y.XmlElement|Y.XmlText|null
prevSibling:Y.XmlElement|Y.XmlText|null
insert(index:number, content:Array<Y.XmlElement|Y.XmlText>)
delete(index:number, length:number)
get(index:number)
length:number
setAttribute(attributeName:string, attributeValue:string)
removeAttribute(attributeName:string)
getAttribute(attributeName:string):string
getAttributes():Object<string,string>
get(i:number):Y.XmlElement|Y.XmlText
- Retrieve the i-th element.
slice(start:number, end:number):Array<Y.XmlElement|Y.XmlText>
- Retrieve a range of content
clone():Y.XmlElement
- Clone this type into a fresh Yjs type.
toArray():Array<Y.XmlElement|Y.XmlText>
- Copies the children to a new Array.
toDOM():Element
- Transforms this type and all children to a new DOM element.
toString():string
- Get the XML serialization of all descendants.
toJSON():string
- See
toString
.
observe(function(YXmlEvent, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every
time this type is modified. In the case this type is modified in the event
listener, the event listener will be called again after the current event
listener returns.
unobserve(function(YXmlEvent, Transaction):void)
-
Removes an
observe
event listener from this type.
observeDeep(function(Array<YEvent>, Transaction):void)
-
Adds an event listener to this type that will be called synchronously every time
this type or any of its children is modified. In the case this type is modified
in the event listener, the event listener will be called again after the current
event listener returns. The event listener receives all Events created by itself
or any of its children.
unobserveDeep(function(Array<YEvent>, Transaction):void)
-
Removes an
observeDeep
event listener from this type.
Y.Doc
const doc = new Y.Doc()
clientID
- A unique id that identifies this client. (readonly)
gc
-
Whether garbage collection is enabled on this doc instance. Set `doc.gc = false`
in order to disable gc and be able to restore old content. See https://github.com/yjs/yjs#yjs-crdt-algorithm
for more information about gc in Yjs.
transact(function(Transaction):void [, origin:any])
-
Every change on the shared document happens in a transaction. Observer calls and
the
update
event are called after each transaction. You should
bundle changes into a single transaction to reduce the amount of event
calls. I.e. doc.transact(() => { yarray.insert(..); ymap.set(..) })
triggers a single change event.
You can specify an optional origin
parameter that is stored on transaction.origin
and
on('update', (update, origin) => ..)
.
toJSON():any
-
Deprecated: It is recommended to call toJSON directly on the shared types.
Converts the entire document into a js object, recursively traversing each yjs
type. Doesn't log types that have not been defined (using
ydoc.getType(..)
).
get(string, Y.[TypeClass]):[Type]
- Define a shared type.
getArray(string):Y.Array
- Define a shared Y.Array type. Is equivalent to
y.get(string, Y.Array)
.
getMap(string):Y.Map
- Define a shared Y.Map type. Is equivalent to
y.get(string, Y.Map)
.
getText(string):Y.Text
- Define a shared Y.Text type. Is equivalent to
y.get(string, Y.Text)
.
getXmlElement(string, string):Y.XmlElement
- Define a shared Y.XmlElement type. Is equivalent to
y.get(string, Y.XmlElement)
.
getXmlFragment(string):Y.XmlFragment
- Define a shared Y.XmlFragment type. Is equivalent to
y.get(string, Y.XmlFragment)
.
on(string, function)
- Register an event listener on the shared type
off(string, function)
- Unregister an event listener from the shared type
Y.Doc Events
on('update', function(updateMessage:Uint8Array, origin:any, Y.Doc):void)
-
Listen to document updates. Document updates must be transmitted to all other
peers. You can apply document updates in any order and multiple times. Use `updateV2`
to receive V2 events.
on('beforeTransaction', function(Y.Transaction, Y.Doc):void)
- Emitted before each transaction.
on('afterTransaction', function(Y.Transaction, Y.Doc):void)
- Emitted after each transaction.
on('beforeAllTransactions', function(Y.Doc):void)
-
Transactions can be nested (e.g. when an event within a transaction calls another
transaction). Emitted before the first transaction.
on('afterAllTransactions', function(Y.Doc, Array<Y.Transaction>):void)
- Emitted after the last transaction is cleaned up.
Document Updates
Changes on the shared document are encoded into document updates. Document
updates are commutative and idempotent. This means that they can be applied
in any order and multiple times.
Example: Listen to update events and apply them on remote client
const doc1 = new Y.Doc()
const doc2 = new Y.Doc()
doc1.on('update', update => {
Y.applyUpdate(doc2, update)
})
doc2.on('update', update => {
Y.applyUpdate(doc1, update)
})
doc1.getArray('myarray').insert(0, ['Hello doc2, you got this?'])
doc2.getArray('myarray').get(0)
Yjs internally maintains a state vector that denotes the next
expected clock from each client. In a different interpretation it holds the
number of structs created by each client. When two clients sync, you can either
exchange the complete document structure or only the differences by sending the
state vector to compute the differences.
Example: Sync two clients by exchanging the complete document structure
const state1 = Y.encodeStateAsUpdate(ydoc1)
const state2 = Y.encodeStateAsUpdate(ydoc2)
Y.applyUpdate(ydoc1, state2)
Y.applyUpdate(ydoc2, state1)
Example: Sync two clients by computing the differences
This example shows how to sync two clients with the minimal amount of exchanged
data by computing only the differences using the state vector of the remote
client. Syncing clients using the state vector requires another roundtrip, but
can save a lot of bandwidth.
const stateVector1 = Y.encodeStateVector(ydoc1)
const stateVector2 = Y.encodeStateVector(ydoc2)
const diff1 = Y.encodeStateAsUpdate(ydoc1, stateVector2)
const diff2 = Y.encodeStateAsUpdate(ydoc2, stateVector1)
Y.applyUpdate(ydoc1, diff2)
Y.applyUpdate(ydoc2, diff1)
Example: Syncing clients without loading the Y.Doc
It is possible to sync clients and compute delta updates without loading the Yjs
document to memory. Yjs exposes an API to compute the differences directly on the
binary document updates.
let currentState1 = Y.encodeStateAsUpdate(ydoc1)
let currentState2 = Y.encodeStateAsUpdate(ydoc2)
ydoc1.destroy()
ydoc2.destroy()
const stateVector1 = Y.encodeStateVectorFromUpdate(currentState1)
const stateVector2 = Y.encodeStateVectorFromUpdate(currentState2)
const diff1 = Y.diffUpdate(currentState1, stateVector2)
const diff2 = Y.diffUpdate(currentState2, stateVector1)
currentState1 = Y.mergeUpdates([currentState1, diff2])
currentState2 = Y.mergeUpdates([currentState2, diff1])
Obfuscating Updates
If one of your users runs into a weird bug (e.g. the rich-text editor throws
error messages), then you don't have to request the full document from your
user. Instead, they can obfuscate the document (i.e. replace the content with
meaningless generated content) before sending it to you. Note that someone might
still deduce the type of content by looking at the general structure of the
document. But this is much better than requesting the original document.
Obfuscated updates contain all the CRDT-related data that is required for
merging. So it is safe to merge obfuscated updates.
const ydoc = new Y.Doc()
ydoc.getText().insert(0, 'hello world')
const update = Y.encodeStateAsUpdate(ydoc)
const obfuscatedUpdate = Y.obfuscateUpdate(update)
const ydoc2 = new Y.Doc()
Y.applyUpdate(ydoc2, obfuscatedUpdate)
ydoc2.getText().toString()
Using V2 update format
Yjs implements two update formats. By default you are using the V1 update format.
You can opt-in into the V2 update format wich provides much better compression.
It is not yet used by all providers. However, you can already use it if
you are building your own provider. All below functions are available with the
suffix "V2". E.g. Y.applyUpdate
⇒ Y.applyUpdateV2
. Also when listening to updates
you need to specifically need listen for V2 events e.g. yDoc.on('updateV2', …)
.
We also support conversion functions between both formats:
Y.convertUpdateFormatV1ToV2
& Y.convertUpdateFormatV2ToV1
.
Update API
Y.applyUpdate(Y.Doc, update:Uint8Array, [transactionOrigin:any])
-
Apply a document update on the shared document. Optionally you can specify
transactionOrigin
that will be stored on
transaction.origin
and ydoc.on('update', (update, origin) => ..)
.
Y.encodeStateAsUpdate(Y.Doc, [encodedTargetStateVector:Uint8Array]):Uint8Array
-
Encode the document state as a single update message that can be applied on the
remote document. Optionally specify the target state vector to only write the
differences to the update message.
Y.encodeStateVector(Y.Doc):Uint8Array
- Computes the state vector and encodes it into an Uint8Array.
Y.mergeUpdates(Array<Uint8Array>)
-
Merge several document updates into a single document update while removing
duplicate information. The merged document update is always smaller than
the separate updates because of the compressed encoding.
Y.encodeStateVectorFromUpdate(Uint8Array): Uint8Array
-
Computes the state vector from a document update and encodes it into an Uint8Array.
Y.diffUpdate(update: Uint8Array, stateVector: Uint8Array): Uint8Array
-
Encode the missing differences to another update message. This function works
similarly to
Y.encodeStateAsUpdate(ydoc, stateVector)
but works
on updates instead.
convertUpdateFormatV1ToV2
-
Convert V1 update format to the V2 update format.
convertUpdateFormatV2ToV1
-
Convert V2 update format to the V1 update format.
Relative Positions
When working with collaborative documents, we often need to work with positions.
Positions may represent cursor locations, selection ranges, or even assign a
comment to a range of text. Normal index-positions (expressed as integers) are
not convenient to use because the index-range is invalidated as soon as a remote
change manipulates the document. Relative positions give you a powerful API to
express positions.
A relative position is fixated to an element in the shared document and is not
affected by remote changes. I.e. given the document "a|c"
, the relative
position is attached to c
. When a remote user modifies the document by
inserting a character before the cursor, the cursor will stay attached to the
character c
. insert(1, 'x')("a|c") = "ax|c"
. When the relative position is
set to the end of the document, it will stay attached to the end of the
document.
Example: Transform to RelativePosition and back
const relPos = Y.createRelativePositionFromTypeIndex(ytext, 2)
const pos = Y.createAbsolutePositionFromRelativePosition(relPos, doc)
pos.type === ytext
pos.index === 2
Example: Send relative position to remote client (json)
const relPos = Y.createRelativePositionFromTypeIndex(ytext, 2)
const encodedRelPos = JSON.stringify(relPos)
const parsedRelPos = JSON.parse(encodedRelPos)
const pos = Y.createAbsolutePositionFromRelativePosition(parsedRelPos, remoteDoc)
pos.type === remoteytext
pos.index === 2
Example: Send relative position to remote client (Uint8Array)
const relPos = Y.createRelativePositionFromTypeIndex(ytext, 2)
const encodedRelPos = Y.encodeRelativePosition(relPos)
const parsedRelPos = Y.decodeRelativePosition(encodedRelPos)
const pos = Y.createAbsolutePositionFromRelativePosition(parsedRelPos, remoteDoc)
pos.type === remoteytext
pos.index === 2
Y.createRelativePositionFromTypeIndex(type:Uint8Array|Y.Type, index: number
[, assoc=0])
-
Create a relative position fixated to the i-th element in any sequence-like
shared type (if
assoc >= 0
). By default, the position associates
with the character that comes after the specified index position. If
assoc < 0
, then the relative position associates with the character
before the specified index position.
Y.createAbsolutePositionFromRelativePosition(RelativePosition, Y.Doc):
{ type: Y.AbstractType, index: number, assoc: number } | null
-
Create an absolute position from a relative position. If the relative position
cannot be referenced, or the type is deleted, then the result is null.
Y.encodeRelativePosition(RelativePosition):Uint8Array
-
Encode a relative position to an Uint8Array. Binary data is the preferred
encoding format for document updates. If you prefer JSON encoding, you can
simply JSON.stringify / JSON.parse the relative position instead.
Y.decodeRelativePosition(Uint8Array):RelativePosition
- Decode a binary-encoded relative position to a RelativePositon object.
Y.UndoManager
Yjs ships with an Undo/Redo manager for selective undo/redo of changes on a
Yjs type. The changes can be optionally scoped to transaction origins.
const ytext = doc.getText('text')
const undoManager = new Y.UndoManager(ytext)
ytext.insert(0, 'abc')
undoManager.undo()
ytext.toString()
undoManager.redo()
ytext.toString()
constructor(scope:Y.AbstractType|Array<Y.AbstractType>
[, {captureTimeout:number,trackedOrigins:Set<any>,deleteFilter:function(item):boolean}])
- Accepts either single type as scope or an array of types.
undo()
redo()
stopCapturing()
on('stack-item-added', { stackItem: { meta: Map<any,any> }, type: 'undo'
| 'redo' })
-
Register an event that is called when a
StackItem
is added to the
undo- or the redo-stack.
on('stack-item-updated', { stackItem: { meta: Map<any,any> }, type: 'undo'
| 'redo' })
-
Register an event that is called when an existing
StackItem
is updated.
This happens when two changes happen within a "captureInterval".
on('stack-item-popped', { stackItem: { meta: Map<any,any> }, type: 'undo'
| 'redo' })
-
Register an event that is called when a
StackItem
is popped from
the undo- or the redo-stack.
on('stack-cleared', { undoStackCleared: boolean, redoStackCleared: boolean })
-
Register an event that is called when the undo- and/or the redo-stack is cleared.
Example: Stop Capturing
UndoManager merges Undo-StackItems if they are created within time-gap
smaller than options.captureTimeout
. Call um.stopCapturing()
so that the next
StackItem won't be merged.
ytext.insert(0, 'a')
ytext.insert(1, 'b')
undoManager.undo()
ytext.toString()
ytext.insert(0, 'a')
undoManager.stopCapturing()
ytext.insert(0, 'b')
undoManager.undo()
ytext.toString()
Example: Specify tracked origins
Every change on the shared document has an origin. If no origin was specified,
it defaults to null
. By specifying trackedOrigins
you can
selectively specify which changes should be tracked by UndoManager
. The
UndoManager instance is always added to trackedOrigins
.
class CustomBinding {}
const ytext = doc.getText('text')
const undoManager = new Y.UndoManager(ytext, {
trackedOrigins: new Set([42, CustomBinding])
})
ytext.insert(0, 'abc')
undoManager.undo()
ytext.toString()
ytext.delete(0, 3)
doc.transact(() => {
ytext.insert(0, 'abc')
}, 42)
undoManager.undo()
ytext.toString()
doc.transact(() => {
ytext.insert(0, 'abc')
}, 41)
undoManager.undo()
ytext.toString()
ytext.delete(0, 3)
doc.transact(() => {
ytext.insert(0, 'abc')
}, new CustomBinding())
undoManager.undo()
ytext.toString()
Example: Add additional information to the StackItems
When undoing or redoing a previous action, it is often expected to restore
additional meta information like the cursor location or the view on the
document. You can assign meta-information to Undo-/Redo-StackItems.
const ytext = doc.getText('text')
const undoManager = new Y.UndoManager(ytext, {
trackedOrigins: new Set([42, CustomBinding])
})
undoManager.on('stack-item-added', event => {
event.stackItem.meta.set('cursor-location', getRelativeCursorLocation())
})
undoManager.on('stack-item-popped', event => {
restoreCursorLocation(event.stackItem.meta.get('cursor-location'))
})
Yjs CRDT Algorithm
Conflict-free replicated data types (CRDT) for collaborative editing are an
alternative approach to operational transformation (OT). A very simple
differentiation between the two approaches is that OT attempts to transform
index positions to ensure convergence (all clients end up with the same
content), while CRDTs use mathematical models that usually do not involve index
transformations, like linked lists. OT is currently the de-facto standard for
shared editing on text. OT approaches that support shared editing without a
central source of truth (a central server) require too much bookkeeping to be
viable in practice. CRDTs are better suited for distributed systems, provide
additional guarantees that the document can be synced with remote clients, and
do not require a central source of truth.
Yjs implements a modified version of the algorithm described in this
paper.
This article
explains a simple optimization on the CRDT model and
gives more insight about the performance characteristics in Yjs.
More information about the specific implementation is available in
INTERNALS.md and in
this walkthrough of the Yjs codebase.
CRDTs that are suitable for shared text editing suffer from the fact that they
only grow in size. There are CRDTs that do not grow in size, but they do not
have the characteristics that are benificial for shared text editing (like
intention preservation). Yjs implements many improvements to the original
algorithm that diminish the trade-off that the document only grows in size. We
can't garbage collect deleted structs (tombstones) while ensuring a unique
order of the structs. But we can 1. merge preceeding structs into a single
struct to reduce the amount of meta information, 2. we can delete content from
the struct if it is deleted, and 3. we can garbage collect tombstones if we
don't care about the order of the structs anymore (e.g. if the parent was
deleted).
Examples:
- If a user inserts elements in sequence, the struct will be merged into a
single struct. E.g.
text.insert(0, 'a'), text.insert(1, 'b');
is
first represented as two structs ([{id: {client, clock: 0}, content: 'a'}, {id: {client, clock: 1}, content: 'b'}
) and then merged into a single
struct: [{id: {client, clock: 0}, content: 'ab'}]
. - When a struct that contains content (e.g.
ItemString
) is deleted, the
struct will be replaced with an ItemDeleted
that does not contain content
anymore. - When a type is deleted, all child elements are transformed to
GC
structs. A
GC
struct only denotes the existence of a struct and that it is deleted.
GC
structs can always be merged with other GC
structs if the id's are
adjacent.
Especially when working on structured content (e.g. shared editing on
ProseMirror), these improvements yield very good results when
benchmarking random document edits.
In practice they show even better results, because users usually edit text in
sequence, resulting in structs that can easily be merged. The benchmarks show
that even in the worst case scenario that a user edits text from right to left,
Yjs achieves good performance even for huge documents.
State Vector
Yjs has the ability to exchange only the differences when syncing two clients.
We use lamport timestamps to identify structs and to track in which order a
client created them. Each struct has an struct.id = { client: number, clock: number}
that uniquely identifies a struct. We define the next expected clock
by each client as the state vector. This data structure is similar to the
version vectors data structure.
But we use state vectors only to describe the state of the local document, so we
can compute the missing struct of the remote client. We do not use it to track
causality.
License and Author
Yjs and all related projects are MIT licensed.
Yjs is based on my research as a student at the RWTH
i5. Now I am working on Yjs in my spare time.
Fund this project by donating on GitHub Sponsors
or hiring me as a contractor for your collaborative
app.