Rjs

A faster, more memory-efficient CRDT library for collaborative editing.

Rjs is a drop-in alternative to Yjs that delivers the same functionality with significantly better performance and lower memory usage. Built on block-wise RGA (Replicated Growable Array) with packed numeric IDs, incremental caches, and optimized serialization.

Why Rjs?

Yjs is the most popular CRDT library, but it has known performance bottlenecks in sequential operations, map/array handling, and memory usage. Rjs addresses these by:

• Using packed numeric IDs instead of object-based IDs
• Maintaining linked-list-only block storage without redundant arrays
• Implementing checkpoint caches for O(log n + 32) position lookups
• Using Yjs-compatible binary encoding for the same compact format
• Eliminating O(n) toString() calls from the hot insert path

Performance

Benchmarked with 1000 operations per test, 1000 iterations, median time:

Benchmark	Rjs	Yjs	Speedup
Sequential Insert (1K chars)	0.095ms	3.318ms	34.9x
Random Insert (1K chars)	3.707ms	21.064ms	5.7x
Sequential Delete (1K chars)	1.835ms	4.175ms	2.3x
Map Operations (1K set/del)	0.240ms	2.819ms	11.7x
Array Operations (1K ops)	0.154ms	6.131ms	39.8x
Two-doc Sync (400 edits)	0.692ms	1.406ms	2.0x

Metric	Rjs	Yjs
Memory (5K chars)	6.6 KB	41.8 KB (6.4x less)
Encoded Size (5K chars)	4.9 KB	4.9 KB (equal)

Rjs wins 6 out of 7 benchmarks with identical encoded size.

Installation

npm install github:rudrakumar07/Rjs

Zero runtime dependencies.

Quick Start

const { CRDT } = require('rjs');

// Create a document
const doc = new CRDT(1); // clientId = 1

// Text operations
const text = doc.getText('article');
text.insert(0, 'Hello');
text.insert(5, ' World');
console.log(text.toString()); // "Hello World"

// Map operations
const map = doc.getMap('config');
map.set('theme', 'dark');
map.set('fontSize', 14);
console.log(map.get('theme')); // "dark"

// Array operations
const list = doc.getArray('todos');
list.push('Buy groceries');
list.push('Write code');
console.log(list.toArray()); // ["Buy groceries", "Write code"]

// Counter
const counter = doc.getCounter('likes');
counter.add(5);
counter.add(3);
console.log(counter.value); // 8

Serialization & Sync

const { CRDT, Serializer } = require('rjs');
const ser = new Serializer();

// Document A makes changes
const docA = new CRDT(1);
docA.getText('doc').insert(0, 'Hello from A');
docA.getMap('meta').set('author', 'Alice');

// Encode and send to Document B
const update = ser.encodeDocument(docA);

// Document B receives and applies
const docB = new CRDT(2);
ser.decodeDocument(update, docB);

console.log(docB.getText('doc').toString()); // "Hello from A"
console.log(docB.getMap('meta').get('author')); // "Alice"

Undo/Redo

const { CRDT, UndoManager } = require('rjs');

const doc = new CRDT(1);
const text = doc.getText('doc');
const undo = new UndoManager(doc);

text.insert(0, 'Hello');
text.insert(5, ' World');
undo.undo();
console.log(text.toString()); // "Hello"
undo.redo();
console.log(text.toString()); // "Hello World"

Snapshots

const { CRDT, Snapshot } = require('rjs');

const doc = new CRDT(1);
const text = doc.getText('doc');
text.insert(0, 'Version 1');

// Take a snapshot
const snapshot = Snapshot.createFromDocument(doc);

// Make more changes
text.insert(8, ' and more');

// Restore from snapshot
const restored = Snapshot.createDocFromSnapshot(doc, snapshot, doc.clientId);
console.log(restored.getText('doc').toString()); // "Version 1"

XML Types

const { CRDT } = require('rjs');

const doc = new CRDT(1);
const root = doc.getXmlFragment('editor');

const paragraph = root.insert(0, 'paragraph');
paragraph.insert(0, 'Hello');
paragraph.setAttribute('class', 'text-xl');

const text = paragraph.insert(0, 'text');
text.insert(0, 'World');

console.log(root.toString()); // '<paragraph class="text-xl"><text>World</text>Hello</paragraph>'

Relative Positions

const { CRDT, RelativePosition } = require('rjs');

const doc = new CRDT(1);
const text = doc.getText('doc');
text.insert(0, 'Hello World');

// Create a relative position at index 5
const relPos = RelativePosition.createFromTypeIndex(text, 5);

// Insert text before the position
text.insert(0, 'Say: ');

// Resolve the relative position
// It should now point to index 10 (shifted by "Say: ".length)

Subdocuments

const { CRDT } = require('rjs');

const doc = new CRDT(1);
const manager = doc.getSubdocs();

// Create a child document
const child = manager.create('child1', { type: 'text' });
child.getText('content').insert(0, 'Nested content');

// Access child
const retrieved = manager.get('child1');
console.log(retrieved.getText('content').toString()); // "Nested content"

Observer Events

const { CRDT } = require('rjs');

const doc = new CRDT(1);
const text = doc.getText('doc');

// Listen for changes
text.observe((event) => {
  console.log('Delta:', event.delta);
  console.log('Target:', event.target.toString());
});

// Listen for deep changes (all types)
doc.on('update', (op) => {
  console.log('Operation:', op);
});

text.insert(0, 'Hello');

Architecture

rjs/
├── lib/
│   └── rjs.js              # Main entry point
├── src/
│   ├── core/
│   │   ├── block_rga.js     # Block-wise RGA engine
│   │   ├── crdt.js          # CRDT types (Text, Map, Array, Counter)
│   │   ├── events.js        # Event system
│   │   ├── helpers.js       # Shared utilities
│   │   ├── id.js            # Packed numeric IDs
│   │   ├── relative_position.js
│   │   ├── snapshot.js      # Snapshots, merge, diff
│   │   ├── subdoc.js        # Subdocument support
│   │   ├── undo.js          # Undo/Redo manager
│   │   └── xml.js           # XML types
│   ├── serialization/
│   │   ├── encoder.js       # Binary encoder/decoder
│   │   ├── serializer.js    # Document serializer
│   │   ├── serializer_yjs.js # Yjs-compatible encoding
│   │   ├── serializer_v2.js  # V2 format
│   │   └── compression.js   # LZW compression
│   ├── memory/
│   │   ├── arena.js         # Memory pool & string interning
│   │   └── gc.js            # Garbage collector
│   ├── net/
│   │   ├── index.js         # Network manager
│   │   ├── protocol.js      # Sync protocol
│   │   └── provider.js      # WebSocket provider
│   ├── perf/
│   │   ├── index.js         # Performance optimizer
│   │   ├── batcher.js       # Operation batching
│   │   └── cache.js         # Result caching
│   └── storage/
│       └── index.js         # Persistent storage
├── test.js                  # 222 functional tests
├── tests/
│   ├── run_stress.js        # Stress test runner
│   ├── test_stress_part1.js # 10,000 fuzz tests
│   ├── test_stress_part2.js # 4,100 serialization/sync tests
│   └── test_stress_part3.js # 4,000 edge case/stress tests
├── package.json
├── .gitignore
└── README.md

Testing

Run the functional test suite:

npm test

Run the stress test suite (18,100+ tests):

npm run stress-test

How Rjs Compares to Yjs

Feature	Rjs	Yjs
Text CRDT	Yes	Yes
Map CRDT	Yes	Yes
Array CRDT	Yes	Yes
Counter CRDT	Yes	Yes
XML Types	Yes	Yes
Undo/Redo	Yes	Yes
Snapshots	Yes	Yes
Relative Positions	Yes	Yes
Subdocuments	Yes	Yes
Encoding Format	Yjs V2 compatible	V1/V2
Zero Dependencies	Yes	Yes
Sequential Insert	34.9x faster	Baseline
Map Operations	11.7x faster	Baseline
Array Operations	39.8x faster	Baseline
Memory Usage	6.4x less	Baseline

License

MIT