Loro is a CRDTs(Conflict-free Replicated Data Types) library that makes building local-first and collaborative apps easier. You can now use it in Rust, JS (via WASM), and Swift.

Features

Features Provided by CRDTs

• P2P Synchronization
• Automatic Merging
• Local Availability
• Scalability
• Delta Updates

Supported CRDT Algorithms

• 📝 Text Editing with Fugue
• 📙 Rich Text CRDT
• 🌲 Moveable Tree
• 🚗 Moveable List
• 🗺️ Last-Write-Wins Map

Advanced Features in Loro

• 🚀 Fast Document Loading
• ⏱️ Fast Time Travel Through History
• 🏛️ Version Control with Real-Time Collaboration
• 📦 Shallow Snapshot that Works like Git Shallow Clone

In this example, we demonstrate importing an entire Loro codebase into a Loro-powered version controller, preserving the complete Git DAG history while enabling fast version switching.

Debugging the Wasm build

The standard build pipeline (deno run -A ./scripts/build.ts dev|release) now keeps DWARF debugging information through wasm-bindgen and emits two helper files alongside every loro_wasm_bg.wasm artifact:

• loro_wasm_bg.wasm.map — a v3 source map derived from DWARF so that Chrome, Edge, and Firefox can show original Rust locations when inspecting stack traces.

Load the source map in browser devtools; when devtools fetches the debug companion it can map instructions back to Rust source files and line numbers without inflating the shipped .wasm.

Example

import { expect, test } from 'vitest';
import { LoroDoc, LoroList } from 'loro-crdt';

test('sync example', () => {
  // Sync two docs with two rounds of exchanges

  // Initialize document A
  const docA = new LoroDoc();
  const listA: LoroList = docA.getList('list');
  listA.insert(0, 'A');
  listA.insert(1, 'B');
  listA.insert(2, 'C');

  // Export all updates from docA
  const bytes: Uint8Array = docA.export({ mode: 'update' });

  // Simulate sending `bytes` across the network to another peer, B

  const docB = new LoroDoc();
  // Peer B imports the updates from A
  docB.import(bytes);

  // B's state matches A's state
  expect(docB.toJSON()).toStrictEqual({
    list: ['A', 'B', 'C'],
  });

  // Get the current version of docB
  const version = docB.oplogVersion();

  // Simulate editing at B: delete item 'B'
  const listB: LoroList = docB.getList('list');
  listB.delete(1, 1);

  // Export the updates from B since the last sync point
  const bytesB: Uint8Array = docB.export({ mode: 'update', from: version });

  // Simulate sending `bytesB` back across the network to A

  // A imports the updates from B
  docA.import(bytesB);

  // A has the same state as B
  expect(docA.toJSON()).toStrictEqual({
    list: ['A', 'C'],
  });
});

Blog

• Loro 1.0
• Movable tree CRDTs and Loro's implementation
• Introduction to Loro's Rich Text CRDT
• Loro: Reimagine State Management with CRDTs

Credits

Loro draws inspiration from the innovative work of the following projects and individuals:

• Diamond-types: The Event Graph Walker (Eg-walker) algorithm from @josephg has been adapted to reduce the computation and space usage of CRDTs.
• Automerge: Their use of columnar encoding for CRDTs has informed our strategies for efficient data encoding.
• Yjs: We have incorporated a similar algorithm for effectively merging collaborative editing operations, thanks to their pioneering work.
• Matthew Weidner: His work on the Fugue algorithm has been invaluable, enhancing our text editing capabilities.
• Martin Kleppmann: His work on CRDTs has significantly influenced our comprehension of the field.