JS SDK
Through Yorkie JS SDK, you can efficiently build collaborative applications. On the client-side implementation, you can create Documents that are automatically synced with remote peers with minimal effort.
If you want to install the SDK, refer to the Getting Started with JS SDK.
Client
Client
is a normal client that can communicate with the server. It has documents and sends changes of the document from local to the server to synchronize with other replicas remotely.
Creating a Client
We can create a Client using new yorkie.Client()
. After the Client has been activated, it is connected to the server and ready to use.
1const client = new yorkie.Client('https://api.yorkie.dev', {2 apiKey: 'xxxxxxxxxxxxxxxxxxxx',3});4await client.activate();
The API key is used to identify the project in Yorkie. You can get the API key of the project you created in the Dashboard.
Subscribing to Client events
We can use client.subscribe
to subscribe to client-based events, such as status-changed
, stream-connection-status-changed
.
1const unsubscribe = client.subscribe((event) => {2 if (event.type === 'status-changed') {3 console.log(event.value); // 'activated' or 'deactivated'4 } else if (event.type === 'stream-connection-status-changed') {5 console.log(event.value); // 'connected' or 'disconnected'6 }7});
By using the value of the stream-connection-status-changed
event, it is possible to determine whether the Client is connected to the network.
If you want to know about other client events, please refer to the ClientEvent, and ClientEventType.
Document
Document
is a primary data type in Yorkie, which provides a JSON-like updating experience that makes it easy to represent your application's model.
A Document
can be updated without being attached to the client, and its changes are automatically propagated to other clients when the Document
is attached to the Client
or when the network is restored.
Creating a Document
We can create a Document using yorkie.Document()
. Let's create a Document with a key and attach it to the Client.
1const doc = new yorkie.Document('doc-1');
The document key is used to identify the Document in Yorkie. It is a string that can be freely defined by the user.
However, it is allowed to use only a-z
, A-Z
, 0-9
, -
, .
, _
, ~
and must be less than 120 characters.
Attaching the Document
When you attach, the client notifies the server that it is subscribing to this document. If the document does not exist on the server, it will be created, and any local changes that occurred will be updated to the server's document. If the server already has a document associated with the provided key, it sends the existing changes to the client, which are then applied to synchronize the document.
Once attached, the document becomes synchronized with other clients. This ensures that any modifications made by one client are instantly propagated to other clients collaborating on the same document.
The second argument is options.
initialPresence
: Sets the initial presence of the client that attaches the document. The presence is shared with other users participating in the document. It must be serializable to JSON.isRealtimeSync
(Optional): Specifies whether to enable real-time synchronization. The default value istrue
, which means synchronization occurs automatically. If set tofalse
, you should manually control the synchronization.
1await client.attach(doc, {2 initialPresence: { color: 'blue', cursor: { x: 0, y: 0 } },3 isRealtimeSync: true,4});
Updating presence
The Document.update()
method allows you to make changes to the state of the current user's presence.
Specific properties provided will be changed. The existing presence object will be updated by merging the new changes. In other words, properties not specified in the update function will remain unchanged.
1doc.update((root, presence) => {2 presence.set({ cursor: { x: 1, y: 1 } });3});45// final state6// presence = { color: 'blue', cursor: { x: 1, y: 1 } }7// we can see that the changes made were merged and the final state of the current user's presence is as we desire
Note, the properties provided will be replaced entirely and not merely updated.
For example:
1await client.attach(doc, {2 // let's say 'color' is a property of cursor3 initialPresence: {cursor: { x: 0, y: 0, color: 'red'}},4});56doc.update((root, presence) => {7 // we want to change the x y coordinates of our cursor8 presence.set({ cursor: { x: 1, y: 1 } });9});101112// final state13// presence = { cursor: { x: 1, y: 1 } }14// we can see that all properties inside cursor get replaced (i.e. we lose the property 'color')
Getting presence
Document.getPresence(clientID)
It returns the presence of a specific client.
1doc.getPresence(client.getID()); // { color: 'blue', cursor: { x: 1, y: 1 } }
Document.getMyPresence()
It returns the presence of the current client that has attached to the document.
1doc.getMyPresence(); // { color: 'blue', cursor: { x: 1, y: 1 } }
Document.getPresences()
It returns an array about all clients currently participating in the document. Each entry in the array includes the client's id and presence.
1const users = doc.getPresences();2for (const { clientID, presence } of users ) {3 // Do something4}
Displaying users
Here is an example of showing a list of users participating in the collaborative application.
Document.subscribe("presence")
This method allows you to subscribe to all presence-related changes. By subscribing to these events, you can be notified when specific changes occur within the document, such as clients attaching, detaching, or modifying their presence.
1const unsubscribe = doc.subscribe("presence", (event) => {2 if (event.type === "initialized") {3 // Array of other users currently participating in the document4 // event.value;5 }67 if (event.type === "watched") {8 // A user has joined the document editing in online9 // event.value;10 }1112 if (event.type === "unwatched") {13 // A user has left the document editing14 // event.value;15 }1617 if (event.type === "presence-changed") {18 // A user has updated their presence19 // event.value;20 }21});
Document.subscribe("my-presence")
This method is specifically for subscribing to changes in the presence of the current client that has attached to the document.
The possible event.type are: initialized
, presence-changed
.
1const unsubscribe = doc.subscribe("my-presence", (event) => {2 // Do something3});
Document.subscribe("others")
This method enables you to subscribe to changes in the presence of other clients participating in the document.
The possible event.type are: watched
, unwatched
, presence-changed
.
1const unsubscribe = doc.subscribe("others", (event) => {2 if (event.type === "watched") {3 addUser(event.value);4 }56 if (event.type === "unwatched") {7 removeUser(event.value);8 }910 if (event.type === "presence-changed") {11 updateUser(event.value);12 }13});
Editing the Document
Document.update(changeFn, message)
enables you to modify a Document. The optional message
allows you to add a description to the change. If the Document is attached to the Client, all changes are automatically synchronized with other Clients.
1const message = 'update document for test';2doc.update((root) => {3 root.todos = [];4 root.todos.push('todo-1');5 root.obj = {6 name: 'yorkie',7 age: 14,8 };9 root.counter = new yorkie.Counter(yorkie.IntType, 0);10 root.counter.increase(1);11}, message);
Under the hood, root
in the update
function creates a change
, a set of operations, using a JavaScript proxy. Every element has its unique ID, created by the logical clock. This ID is used by Yorkie to track which object is which.
You can get the contents of the Document using document.getRoot()
.
1const root = doc.getRoot();2console.log(root.todos); // ["todo-1"]3console.log(root.obj); // {"name":"yorkie","age":14}4console.log(root.obj.name); // "yorkie"5console.log(root.counter.getValue()); // 1
Subscribing to Document
Document.subscribe()
A Document can be modified by changes generated remotely or locally in Yorkie.
Whenever the Document is modified, change events are triggered and we can subscribe to these events using the document.subscribe(callback)
.
The callback is called with an event object, and the event.type
property indicates the source of the change, which can be one of the following values: local-change
, remote-change
, or snapshot
.
When the event.type
is local-change
or remote-change
, the event.value
is a changeInfo, which has {operations, message}
properties.
For more information about changeInfo for document events, please refer to the ChangeInfo.
1const unsubscribe = doc.subscribe((event) => {2 if (event.type === 'local-change') {3 console.log(event);4 } else if (event.type === 'remote-change') {5 // `message` delivered when calling document.update6 const { message, operations } = event.value;78 for (const op of operations) {9 // ex) { type: 'increase', value: 1, path: '$.counter' }10 switch (op.type) {11 case 'increase':12 // Do something...13 break;14 }15 }16 }17});
Document.subscribe("$.path")
Additionally, you can subscribe to changes for a specific path in the Document using doc.subscribe(path, callback)
with a path argument, such as $.todos
, where the $
sign indicates the root of the document.
The callback function is called when the target path and its nested values are changed.
With this feature, you can easily subscribe to changes for a specific part of the document and perform different actions based on the updated values.
1const unsubscribe = doc.subscribe('$.todos', (event) => {2 // The callback will be called when the root.todos or any of its nested values change.3 const target = doc.getValueByPath('$.todos') // you can get the value by path4 // Do something...5});
Changing Synchronization Setting
To change the synchronization setting for a document, you can use client.pause(doc)
and client.resume(doc)
.
When you pause a document, the synchronization process will no longer occur in realtime, and you will need to manually execute the synchronization to ensure that the changes are propagated to other clients.
To resume the realtime synchronization, you can call client.resume(doc)
.
1// 1. Pause real-time sync2await client.pause(doc);3await client.sync(doc); // To perform synchronization, you need to manually call the sync function45// 2. Resume real-time sync6await client.resume(doc);
Changing Synchronization Mode
By default, Yorkie synchronizes a document in push-pull
mode, where local changes are pushed to the server, and remote changes are pulled from the server.
If you only want to send your changes and not receive remote changes, you can use push-only
mode.
For realtime synchronization, you can use client.pauseRemoteChanges(doc)
and client.resumeRemoteChanges(doc)
.
For manual synchronization, you can pass the desired sync mode to client.sync(doc, syncMode)
.
1// Pause remote changes for realtime sync2client.pauseRemoteChanges(doc);3// Resume remote changes for realtime sync4client.resumeRemoteChanges(doc);56// Manual sync in Push-Only mode7await client.sync(doc, SyncMode.PushOnly);8// Manual sync in Push-Pull mode9await client.sync(doc, SyncMode.PushPull);
Detaching the Document
If the document is no longer used, it should be detached to increase the efficiency of GC removing CRDT tombstones. For more information about GC, please refer to Garbage Collection.
1await client.detach(doc);
Custom CRDT types
Custom CRDT types are data types that can be used for special applications such as text editors and counters, unlike general JSON data types such as Object
and Array
. Custom CRDT types can be created in the callback function of document.update
.
Text
Text
provides supports for collaborative text editing. In addition, contents in Text
can have attributes; for example, characters can be bold, italic, or underlined.
1doc.update((root) => {2 root.text = new yorkie.Text(); // {"text":""}3 root.text.edit(0, 0, 'hello'); // {"text":"hello"}4 root.text.edit(0, 1, 'H'); // {"text":"Hello"}5 root.text.setStyle(0, 1, { bold: true }); // {"text":"<b>H</b>ello"}6});
Selection using presence
The temporary client information, such as text selection, does not need to be stored in the document permanently.
Instead, it can be effectively shared using presence
.
When transmitting text selection information, it is essential to convert the index
, which can vary based on the text state, into the position
used by Yorkie.Text
.
This converted position selection can then be sent and applied through presence.
Here is an example where presence is used to share text selection between users in CodeMirror editor.
- When the text selection is changed:
1// Update selection through text editing2codemirror.on('beforeChange', (cm, change) => {3 doc.update((root, presence) => {4 const range = root.content.edit(from, to, content); // return updated index range5 presence.set({6 selection: root.content.indexRangeToPosRange(range), // update presence7 });8 });9});1011// Update selection using mouse or keyboard12codemirror.on('beforeSelectionChange', (cm, change) => {13 const fromIdx = cm.indexFromPos(change.ranges[0].anchor);14 const toIdx = cm.indexFromPos(change.ranges[0].head);15 doc.update((root, presence) => {16 presence.set({17 selection: root.content.indexRangeToPosRange([fromIdx, toIdx]), // update presence18 });19 });20});
- When applying other user's selection changes:
1doc.subscribe('others', (event) => {2 if (event.type === 'presence-changed') {3 const { clientID, presence } = event.value;4 const range = doc.getRoot().content.posRangeToIndexRange(presence.selection);5 // Handle the updated selection in the editor6 }7});
Text selection can be efficiently shared using presence. Please refer to the following example for a complete code:
- An example of Text co-editing with CodeMirror: CodeMirror example
- An example of Text co-editing with Quill: Quill example
Counter
Counter
supports integer types changing with addition and subtraction. If an integer data needs to be modified simultaneously, Counter
should be used instead of primitives.
1doc.update((root) => {2 root.counter = new yorkie.Counter(yorkie.IntType, 1); // {"counter":1}3 root.counter.increase(2); // {"counter":3}4 root.counter.increase(3); // {"counter":6}5 root.counter.increase(-4); // {"counter":2}6});
TypeScript Support
To use the Document more strictly, we can use type variable in TypeScript when creating a Document.
1import yorkie, { JSONArray } from 'yorkie-js-sdk';2type DocType = {3 list: JSONArray<number>;4 text: yorkie.Text;5};6type PresenceType = {7 username: string;8 color: string;9};1011const doc = new yorkie.Document<DocType, PresenceType>('key');12await client.attach(doc, {13 initialPresence: {14 username: 'alice',15 color: 'blue',16 },17});18doc.update((root, presence) => {19 root.list = [1, 2, 3];20 root.text = new yorkie.Text();21 presence.set({ color: 'red' });22});
Reference
For details on how to use the JS SDK, please refer to JS SDK Reference.