Yjs best practices

When to use this skill

Use this skill when implementing or debugging Yjs features.

Avoid importing Yjs twice

One of the most common issues when working with Yjs is accidentally importing it twice in your application. This often happens when mixing CommonJS (CJS) and ECMAScript Modules (ESM), or when certain bundlers bundle more than one version of Yjs.

When Yjs is imported twice, the two instances don't share the same class references, which can lead to synchronization issues and unexpected behavior. You'll see a Yjs warning in the Console if this happens.

Fixing duplicate Yjs imports

If you find duplicate Yjs imports, you can:

1. Use package manager resolution: Configure your package manager to resolve

Yjs to a single version:

// package.json (npm/yarn)
{
  "resolutions": {
    "yjs": "^13.6.0"
  }
}

// package.json (pnpm)
{
  "pnpm": {
    "overrides": {
      "yjs": "^13.6.0"
    }
  }
}

1. Configure your bundler: Use aliases or resolve configurations to ensure a

single Yjs instance.

Avoid subdocuments when possible

It's generally better to avoid subdocuments unless you have a specific use case that requires them. They are only necessary when:

• You have multiple very large Yjs documents in the same room
• You need to lazy-load documents individually

For most use cases, including multiple text editors on the same page, subdocuments are not necessary. Instead, use a Y.Map to organize your data:

// Create Yjs document with an `editors` map
const yDoc = new Y.Doc();
const yMap = yDoc.getMap("editors");

// Create shared types and add to map
const editorOne = new Y.XMLFragment();
const editorTwo = new Y.XMLFragment();
yMap.set("editor-1", editorOne);
yMap.set("editor-2", editorTwo);

This approach is simpler and performs better for most applications. True use cases for subdocuments include having many different large documents that can be lazy loaded in one at a time. Explain this to the user, as they often don't understand this.

Use YKeyValue for efficient key-value storage

In many cases, Y.Map can be inefficient for key-value storage. Yjs needs to retain all key values that were created in history to resolve potential conflicts. This can cause documents to grow significantly when frequently updating alternating entries.

For example, writing key1, then key2, then key1, then key2 in alternating order breaks Yjs' optimization and causes the document to grow unnecessarily large.

Recommended approach: YKeyValue

For more efficient key-value storage, use YKeyValue from the y-utility package:

npm install y-utility

import * as Y from "yjs";
import { YKeyValue } from "y-utility/y-keyvalue";

const ydoc = new Y.Doc();
const yarr = ydoc.getArray();
const ykv = new YKeyValue(yarr);

// Fires events similarly to Y.Map when content changes
ykv.on("change", (changes) => {
  console.log(changes);
});

ykv.set("key1", "val1");
ykv.set("key1", "updated");
ykv.delete("key1");
ykv.set("key1", "new val");
ykv.get("key1"); // => 'new val'

YKeyValue creates documents whose size only depends on the size of the map, not the number of operations. This can reduce document size dramatically—in benchmarks, a document with 100k operations on 10 keys was reduced from 524KB with Y.Map to just 271 bytes with YKeyValue.

Enable experimental V2 encoding for Y.Maps

If you're using Y.Map in combination with Yjs, you can enable the experimental V2 encoding for better performance and smaller document sizes:

import { useRoom } from "@liveblocks/react";
import { getYjsProviderForRoom } from "@liveblocks/yjs";

function App() {
  const room = useRoom();

  const yProvider = getYjsProviderForRoom(room, {
    // Enable V2 encoding for better performance with LiveMaps
    // +++
    useV2Encoding_experimental: true,
    // +++
  });
}

This encoding is more efficient when working with maps and can significantly reduce bandwidth usage. Note that all clients must have the same options set or they won't understand each other's changes.