QuickJS Javascript Engine

News

• 2026-06-04:
  • New release (Changelog)
• 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.

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 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 ES2025 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 ES2025 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

Benchmarks

• JavaScript engines zoo
• Boa benchmarks
• ahaoboy/js-engine-benchmark

Download

• QuickJS source code: quickjs-2026-06-04.tar.xz
• QuickJS extras (contain the unicode files needed to rebuild the unicode tables and the bench-v8 benchmark): quickjs-extras-2026-06-04.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-2026-06-04.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

• 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.

Links

• Micro QuickJS: a Javascript engine for microcontrollers.

Licensing

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