QuickJS Javascript Engine

News

2025-09-13:
- New release (Changelog)
2025-04-26:
- New release (Changelog). The bignum extensions and the qjscalc application were removed to simplify the code. The BFCalc calculator (web version ) can be used as a replacement for qjscalc.

2024-01-13:
- New release (Changelog)

Introduction

QuickJS is a small and embeddable Javascript engine. It supports the ES2023 specification including modules, asynchronous generators, proxies and BigInt.

Main Features:

Small and easily embeddable: just a few C files, no external dependency, 367 KiB of x86 code for a simple hello world program.
Fast interpreter with very low startup time: runs the 78000 tests of the ECMAScript Test Suite in about 2 minutes on a single core of a desktop PC. The complete life cycle of a runtime instance completes in less than 300 microseconds.
Almost complete ES2023 support including modules, asynchronous generators and full Annex B support (legacy web compatibility).
Passes nearly 100% of the ECMAScript Test Suite tests when selecting the ES2023 features (see test262.fyi).
Can compile Javascript sources to executables with no external dependency.
Garbage collection using reference counting (to reduce memory usage and have deterministic behavior) with cycle removal.
Command line interpreter with contextual colorization implemented in Javascript.
Small built-in standard library with C library wrappers.

Online Demo

qjs can be run in JSLinux.

Benchmarks

Documentation

QuickJS documentation: HTML version, PDF version.

Download

QuickJS source code: quickjs-2025-09-13-2.tar.xz
QuickJS extras (contain the unicode files needed to rebuild the unicode tables and the bench-v8 benchmark): quickjs-extras-2025-09-13.tar.xz
Official GitHub repository.
Binary releases are available here.
Cosmopolitan binaries running on Linux, Mac, Windows, FreeBSD, OpenBSD, NetBSD for both the ARM64 and x86_64 architectures: quickjs-cosmo-2025-09-13.zip.
Typescript compiler compiled with QuickJS: quickjs-typescript-5.9.3-linux-x86.tar.xz
Babel compiler compiled with QuickJS: quickjs-babel-linux-x86.tar.xz

Sub-projects

QuickJS embeds the following C libraries which can be used in other projects:

libregexp: small and fast regexp library fully compliant with the Javascript ES2023 specification.
libunicode: small unicode library supporting case conversion, unicode normalization, unicode script queries, unicode general category queries and all unicode binary properties.
dtoa: small library implementing float64 printing and parsing.

Licensing

QuickJS is released under the MIT license.

Unless otherwise specified, the QuickJS sources are copyright Fabrice Bellard and Charlie Gordon.

Fabrice Bellard - https://bellard.org/