rquickjs

rquickjs

This library is a high level bindings of the QuickJS-NG JavaScript engine, a fork of the QuickJS Javascript engine. Its goal is to be an easy to use, and safe wrapper similar to the rlua library.

QuickJS is a small and embeddable JavaScript engine. It supports the ES2020 specification including modules, asynchronous generators, proxies and BigInt. It optionally supports mathematical extensions such as big decimal floating point numbers (BigDecimal), big binary floating point numbers (BigFloat) and operator overloading.

Main features of QuickJS

• Small and easily embeddable: just a few C files, no external dependency, 210 KiB of x86 code for a simple hello world program.
• Fast interpreter with very low startup time: runs the 75000 tests of the ECMAScript Test Suite in about 100 seconds on a single core of a desktop PC. The complete life cycle of a runtime instance completes in less than 300 microseconds.
• Almost complete ES2020 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 ES2020 features. A summary is available at Test262 Report.
• 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.
• Mathematical extensions: BigDecimal, BigFloat, operator overloading, bigint mode, math mode.
• Command line interpreter with contextual colorization implemented in JavaScript.
• Small built-in standard library with C library wrappers.

Features provided by this crate

• Full integration with async Rust
  • The ES6 Promises can be handled as Rust futures and vice versa
  • Easy integration with almost any async runtime or executor
• Flexible data conversion between Rust and JS
  • Many widely used Rust types can be converted to JS and vice versa
• Support for user-defined allocators
  • The Runtime can be created using custom allocator
  • Using Rust's global allocator is also fully supported
• Support for user-defined module resolvers and loaders which also can be combined to get more flexible solution for concrete case
• Support for bundling JS modules as a bytecode using embed macro
• Support for deferred calling of JS functions
• Full support of ES6 classes
  • Rust data types can be represented as JS classes
  • Data fields can be accessed via object properties
  • Both static and instance members is also supported
  • The properties can be defined with getters and setters
  • Support for constant static properties
  • Support for holding references to JS objects (Data type which holds refs should implement Trace trait to get garbage collector works properly)
  • Support for extending defined classes by JS

Community development

This crate doesn't aim to provide system and web APIs. The QuickJS library is close to V8 in that regard. If you need APIs from WinterGC or Node, then you can take a look at the follow community projects:

• AWS LLRT Modules: Collection of modules that micmic some of the Node APIs in pure Rust
• Rquickjs Extra: Collection of modules that complement AWS LLRT Modules in pure Rust

The community has also built various utilities which might be relevant to you:

• Rquickjs Serde: Serde serializer and deserializer for rquickjs Value

Development status

This bindings is feature complete, mostly stable and ready to use. The error handling is only thing which may change in the future. Some experimental features like parallel may not works as expected. Use it for your own risk.

Supported platforms

Rquickjs needs to compile a C-library which has it's own limitation on supported platforms, furthermore it needs to generate bindings for that platform. As a result rquickjs might not compile on all platforms which rust supports. In general you can allways try to compile rquickjs with the bindgen feature, this should work for most platforms. Rquickjs ships bindings for a limited set of platforms, for these platforms you don't have to enable the bindgen feature. See below for a list of supported platforms.

wasm32-unknown-unknown

wasm32-unknown-unknown is supported out of the box: add rquickjs as a dependency and build for the target. No feature flag, no extra crate, no wasi runtime.

The target ships no libc, so rquickjs-sys supplies the whole OS tail itself:

• quickjs is compiled with the same EMSCRIPTEN / FE_DOWNWARD / FE_UPWARD defines already used for wasi, against a vendored subset of wasi-libc's headers.
• the pure-compute members of wasi-libc (snprintf, strtod, libm, dlmalloc) are linked statically from a vendored libc.a.
• sys/wasm-shim/shim.c replaces every member that would otherwise reach for the host: the clock, localtime_r, abort/__assert_fail, and the stdio backends.

The result imports exactly one host function and nothing else.

The __rquickjs_host_now_us import

The embedder must supply a single import, env.__rquickjs_host_now_us, returning microseconds since the unix epoch as an f64. It backs Date.now(), new Date() and performance-adjacent internals.

const instance = new WebAssembly.Instance(module, {
  env: { __rquickjs_host_now_us: () => Date.now() * 1000 },
});

Time zone data does not exist here, so scripts observe UTC: getTimezoneOffset() is always 0.

Runtime::set_max_stack_size is mandatory

JS_DEFAULT_STACK_SIZE is 1MB, which is exactly the size of the wasm shadow stack. The default computation of stack_top - 1MB therefore wraps, and stack-overflow detection is silently lost: deep recursion becomes a hard trap instead of a catchable RangeError. Always set an explicit limit:

let runtime = Runtime::new()?;
runtime.set_max_stack_size(256 * 1024);

(Defining __wasi__ would also stop the wrap, but quickjs's __wasi__ path pins stack_limit = 0, disabling stack checking outright. That is why the header is patched instead.)

The vendored libc

Rather than downloading a wasi-sysroot at build time, sys/vendor/wasi-libc/ commits the subset actually needed: the prebuilt libc.a from the wasi-sdk-24 release, plus the headers required to compile quickjs against it. It's populated (and updated, after bumping the pinned wasi-sdk version in the script) by scripts/vendor-wasm-libc.sh; see sys/vendor/wasi-libc/NOTICE.md for provenance and licensing.

wasi/api.h guards itself with #ifndef __wasi__ / #error, so the vendoring script writes a copy with that one #error commented out. The rest of the vendored headers are unmodified.

Testing

wasm-test/ builds the safe API as a cdylib and wasm-test/runner.ts drives a battery through it under deno, asserting the import list along the way:

cargo build --manifest-path wasm-test/Cargo.toml --release --target wasm32-unknown-unknown
deno run --allow-read wasm-test/runner.ts

License

This library is licensed under the MIT License