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quickjs-emscripten
Safely execute untrusted Javascript in your Javascript, and execute synchronous code that uses async functions
There is a readme on the project's main page: https://bellard.org/quickjs/
The newsworthy bit here is that the activity seemed to have stalled for year or two and now Fabrice pushed a few fixes and made a new release.
QuickJS is really cool! You can use it to embed JS code in a native binary, which is nice if you're trying to use a NodeJS library outside of the JS ecosystem.
I put together a proof of concept for this about a year ago, in case this is a use case you currently have: https://github.com/ijustlovemath/jescx
Also see quickjs-ng [0], which is a fork in active development. A lot of missing ES features have already been added. [1]
[0] https://github.com/quickjs-ng/quickjs
[1] https://github.com/quickjs-ng/quickjs/issues/54
Based on your comment below I think you figured out the difference - but if you're looking to execute JS, you can pick between ShadowRealm (where available, or using a polyfill) or my library quickjs-emscripten.
Pros of quickjs-emscripten over ShadowRealm:
- You can use quickjs today in any browser with WASM. ShadowRealm isn't available yet, and polyfills have had security issues in the past. See https://www.figma.com/blog/an-update-on-plugin-security/
- In ShadowRealm eval, untrusted code can consume arbitrary CPU cycles. With QuickJS, you can control the CPU time used during an `eval` using an [interrupt handler] that's called periodically during the eval.
- In ShadowRealm eval, untrusted code can allocate arbitrary amounts of memory. With QuickJS, you can control both the [stack size] and the [heap size] available inside the runtime.
- quickjs-emscripten can do interesting things with custom module loaders and facades that allow synchronous code inside the runtime to call async code on the host.
Pros of ShadowRealm over QuickJS:
- ShadowRealm will (presumably?) execute code using your native runtime, probably v8, JavaScriptCore, or SpiderMonkey. Quickjs is orders of magnitude slower than JIT'd javascript performance of v8 etc. It's also slower than v8/JSC's interpreters, although not by a huge amount. See [benchmarks] from 2019.
- You can easily call and pass values to ShadowRealm imported functions. Talking to quickjs-emscripten guest code requires a lot of fiddly and manual object building.
- Overall the quickjs(-emscripten) API is verbose, and requires manual memory management of references to values inside the quickjs runtime.
[interrupt handler]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...
[stack size]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...
[heap size]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...
[benchmarks]: https://bellard.org/quickjs/bench.html