quickjs-ng 0.13.0.1

Thin Python wrapper of quickjs-ng

quickjs-ng

Python wrapper around quickjs-ng, the actively maintained fork of the QuickJS JavaScript engine.

Drop-in replacement for the archived quickjs package — import quickjs works unchanged.

Installation

pip install quickjs-ng

Requires Python ≥ 3.10. Pre-built wheels are available for Linux (x86_64, i686, aarch64), Windows (AMD64, x86), and macOS (arm64), for CPython 3.10+ and PyPy 3.10/3.11.

Usage

import quickjs

# Evaluate expressions
ctx = quickjs.Context()
ctx.eval("1 + 2")  # => 3

# Call JS functions from Python
ctx.eval("function add(a, b) { return a + b; }")
add = ctx.get("add")
add(3, 4)  # => 7

# Call Python functions from JS
ctx.add_callable("py_add", lambda a, b: a + b)
ctx.eval("py_add(3, 4)")  # => 7

# Use the Function helper for thread-safe execution
f = quickjs.Function("f", "function f(x) { return x * 2; }")
f(21)  # => 42

# Resource limits
ctx.set_memory_limit(1024 * 1024)  # 1 MB
ctx.set_time_limit(5)              # 5 seconds of CPU time
ctx.set_max_stack_size(512 * 1024) # 512 KB stack

Threading

Each Context owns an isolated QuickJS runtime — there is no shared state between contexts. A single Context is not thread-safe and must not be used from multiple threads.

Recommended patterns:

• Context per thread — create a separate Context in each thread. No locking, no overhead, full parallelism:

  import threading, quickjs
  
  def worker():
      ctx = quickjs.Context()
      print(ctx.eval("1 + 1"))
  
  threads = [threading.Thread(target=worker) for _ in range(4)]
  for t in threads: t.start()
  

• Function helper — wraps a Context with a dedicated worker thread and lock, safe to call from any thread:

  f = quickjs.Function("f", "function f(x) { return x * 2; }")
  # safe to call f(21) from any thread
  

Pattern	Thread-safe	Overhead
Context per thread	✅	None
Function helper	✅	Small (executor dispatch)
Shared Context	❌	—

Free-threaded Python (3.13t / 3.14t): Both patterns remain safe. The GIL was never relied upon for thread-safety.

musl / Alpine: Worker threads are automatically created with an 8 MB stack (matching glibc defaults) so set_max_stack_size and deep recursion work correctly on musl-based systems.

Versioning

Version format is X.Y.Z.P where X.Y.Z matches the upstream quickjs-ng tag and P is the wrapper patch (starts at 1 per upstream release). Wheels are built automatically when a new upstream tag is detected.

Development

Requires a C compiler and uv.

git clone --recurse-submodules https://github.com/genotrance/quickjs-ng.git
cd quickjs-ng
make install
make test

Target	Description
make install	Create venv, build C extension, install pre-commit
make test	Run tests with coverage
make check	Run linters and type checking
make build	Build sdist and wheel
make clean	Remove build artifacts
make publish	Publish to PyPI

Contributing

Bug reports and pull requests are welcome at https://github.com/genotrance/quickjs-ng/issues.

1. Fork and clone with --recurse-submodules.
2. Run make install to set up the venv, build the C extension, and install pre-commit hooks.
3. Create a feature branch, make changes, add tests in tests/.
4. Run make check && make test — all checks must pass.
5. Open a pull request. CI runs on Ubuntu, Windows, and macOS across Python 3.10–3.14 (including free-threaded 3.13t/3.14t) and PyPy 3.10/3.11.

Documentation

Full technical documentation is in the docs/ folder:

File	Contents
docs/porting.md	Porting history from PetterS/quickjs
docs/c-extension.md	C extension design and stable ABI migration
docs/build.md	Build system: setup.py, pyproject.toml, wheels
docs/ci.md	GitHub Actions workflows
docs/threading.md	Threading model and musl stack fix
docs/testing.md	Test suite layout and memory leak tests
docs/versioning.md	Version scheme and automated stamping
docs/typing.md	Type annotations and mypy configuration

Acknowledgments

This project is a fork of quickjs by Petter Strandmark. The original design of the C bindings, the Function thread-safety wrapper, and the overall API shape are all his work.

The porting to quickjs-ng, the stable ABI migration, the expanded test suite, CICD and all documentation were developed with the assistance of LLMs.

License

MIT