rjs

A lightweight, embeddable JavaScript engine written in Rust, inspired by QuickJS-ng. rjs targets ES2024+ with a focus on correctness, memory safety (zero unsafe in production code paths), small binary size, and competitive interpreter performance — with no JIT, so it runs anywhere QuickJS does (including iOS and WebAssembly).

Highlights

• ES2024+ language: classes, private fields, generators, async/await, modules, destructuring, tagged templates, optional chaining, BigInt, Symbol
• Full RegExp: Unicode property escapes, named groups, lookbehind
• Safe by construction: NaN-boxed values, shape-based objects, reference counting with a cycle collector — all without unsafe in hot paths
• Small and embeddable: workspace of focused crates (core, parser, vm, builtins, regexp, unicode) with a tiny CLI on top
• Conformance-driven: a bundled Test262 runner tracks parity with upstream — current baseline ~83.8% of the curated suite

Quick start

Requires a stable Rust toolchain (edition 2024, pinned in rust-toolchain.toml).

git clone https://github.com/tyrchen/rjs
cd rjs
git submodule update --init --recursive
make build

Run a script:

make run ARGS=path/to/script.js

Or launch the REPL:

make repl

Documentation

• User guide — install, running scripts, REPL, supported language surface, current limitations
• Developer guide — workspace layout, build/test/lint, Test262 runner, contributing
• Docs index
• Design & planning specs

Workspace layout

apps/
  rjs/              CLI entry point (file runner + REPL)
  test262-runner/   Test262 conformance driver
crates/
  core/             Values, objects, GC, runtime, context
  parser/           Lexer + single-pass parser → bytecode
  vm/               Bytecode interpreter
  builtins/         Built-in objects
  regexp/           RegExp compiler + backtracking NFA
  unicode/          Unicode tables and algorithms

Common tasks

Command	What it does
make build	Build the workspace
make test	Run the full test suite via cargo nextest
make check	fmt + lint + test (pre-commit gate)
make run ARGS=foo.js	Execute a JavaScript file
make repl	Start the interactive REPL
make test262-runner	Run the Test262 conformance driver

See the developer guide for the full list.

License

Distributed under the terms of MIT.

See LICENSE for details.

Copyright 2025 Tyr Chen