That said, today Boa has a whole team of maintainers who I’m sure will answer some questions here.
Yes the name does invoke the sense it’s a Python project but I liked it and stuck with it, I saw a Boa snake at a zoo once and knew I wanted to name my next project after it, I was also inspired by Mozilla at the time who named their projects after animals.
Speaking of Mozilla, Boa’s existence came to be because at the time I was working on Servo and wanted to include an all-rust JS engine, one didn’t really exist so I set about making one as a learning exercise, after around 2 years more joined me on that journey and today Boa is around 8 years old. It is not browser grade (although at 94.12% it is more compliant than some browser engines) but that doesn’t matter, plenty of Rust projects have found good use for it as they find it easy to embed and use, so we’re happy.
Another recent thing which we’re very proud is seeing our implementation of Temporal be used in V8 and other engines, so we’re also helping the wider ecosystem and raising all ships! (More here: https://boajs.dev/blog/2025/09/24/temporal-release)
We do hope to improve performance over the next year or so, hopefully that answers some of the Qs here.
Do you see catching up on performance with v8-jitless as a goal or is conformance the primary goal right now? Any plans on doing a JIT? I was always impressed by the idea of Truffle where you implement the language semantics once and you get both interpreter and JIT safely out of it which is a huge source of vulnerabilities in traditional JIT systems
Hi, I'm another one of the maintainers on the project.
In general, we are shifting more to performance now than conformance. We currently sit at around 94% conformance, so there's not really that much more to go conformance-wise. The remaining conformance gains are a couple of the newer specification features and Intl related features. Our current conformance can be found at https://boajs.dev/conformance.
Regarding performance, we are already making some gains, with hopefully more to come. The best example of this was probably the updates to script-bench-rs with our most recent release (which can be found at this commit https://github.com/khvzak/script-bench-rs/commit/d9635de77d2...). We still obviously have more to improve on, but we have already made some pretty steady progress from where we were.
EDIT: I forgot to answer your question about v8-jitless. Obviously in the future it would be nice to be able to be more competitive with v8-jitless, but at least for me, I'd just like to focus on improving the Boa overall.
The past year has been huge for conformance for us, not only we caught up with the top engines but we surpassed them when working on Temporal and having all tests pass for that.
We hope to wind down some of the conformance priority now and focus on performance, we need to work on a new GC, refactor some parts of the engine, and improve various areas.
The idea of a JIT has been raised and we’re not against it, but it’s not on our plans right now (because of the above), that being said there is an open discussion.
Congrats in general! The Temporal in rust release happening in Chrome & others is so cool! So exiting to see such a core piece of work being done & then shared widely among browsers. Speaks well to Rust, the trust folks have in it, and the ability to use Rust from a variety of projects.
There's also a very lovely talk
Cross-Engine Contributions at Scale: How newcomers accelerated Temporal and Upsert in SpiderMonkey, V8, and Boa that goes deep in depth in how technically Temporal was used across engines.
https://www.youtube.com/watch?v=WieD_9BswAE
Thanks! Temporal_rs has been a really fun project to work on, and it's been great to see that it's useful for other engines!
Hopefully, there will be more chances in the future for projects like temporal_rs. Beyond just temporal_rs, I think the Temporal integration in V8 and Kiesel was a good proof of concept for Rust based libraries over FFI using Diplomat.
Hi! I am one of the maintainer of rquickjs and llrt.
Are you looking to build node-like modules anytime soon? I think we could easily port most of the modules I wrote for llrt to your engine.
If we could get rid of the C code in our app, that would make me very happy.
I'm not aware of any plans to build node-like modules, but I think we have the basic support to potentially build them out ... but I could be overlooking or missing something. I'm not personally familiar with them. But defining and using a macro should hopefully be fairly straightforward in Rust with the macros from our latest release (https://boajs.dev/blog/2025/10/22/boa-release-21#boa_module). If we're missing something, feel free to let us know.
Any runtime functionality that has been implemented is available in `boa_runtime`. I've mentioned this elsewhere in the thread, but this crate is not a runtime itself (yet). Currently, it's a collection of runtime features like `console` and `fetch`.
We're looking into the next release potentially being a v1.0, so maybe that option is a bit more possible after that release. But at the same time, I think Servo spends a decent amount of time maintaining the `mozjs` crate, so who knows.
I can't speak exactly for the other maintainers, but for me, I mostly enjoy working on Boa and Boa related things (I've spent the better part of the last year and a half on the temporal implementation). I think it would be cool to have a highly performant and conformant Rust JavaScript engine. So that's my goal :)
I am not meant to be harsh, but note that it fails on a small number of test cases, on v0.21 that is ~900 out of ~50k. Strictly speaking it cannot be described as standard-comforming unless there is some reason behind every failed test. A better way to strive on standard conformance, like QuickJS takes, is to pin down the ecma262 revision and make it 100% compliant.
That may be fair. The better wording may even be specification compliant, but none of the Boa maintainers made this post (we found out about it after the fact).
We, the maintainers, could probably sit down some day and try to triage the failures into a documented txt file, but the overhead on that might make it hard to maintain for an open source project. Plus a large amount of the failures are just new specification features that nobody has implemented yet.
I really appreciate the clear and detailed project description, the only concern is the title on HN. Failing on tests is fine, especially when it demands huge efforts to triage and reiterate on the project structure for them.
Nice to see another contender in this space. If OP is here, can you comment on runtime sandboxing and interop support? Can I selectively disable (or intercept) certain features like network support?
Just to note, Boa is an JavaScript engine / interpreter. We're not a runtime, but we do already have some runtime features implemented in the `boa_runtime` crate, but I don't believe that includes any sandboxing as of right now. It's not even a full fledged runtime ... yet (there's been some discussion about expanding it to a full fledged runtime if anyone has a general interest to work on it). For now, `boa_runtime` is just a collection of features for users to potentially use and if they'd like to implement more, then they are totally welcome to.
There's typically a pretty big difference between an interpreter meant to be embeddable and one that's not. Trying to embed V8 and keep up with V8 API changes would be a huge amount of work. I could see myself using something like this instead of Lua for some projects where V8 would be too much.
My first thought was that this could be interesting for yt-dlp?
Likely similar to something like https://github.com/mlua-rs/mlua - but wanting to execute javascript (instead of lua, and no static libs?) in the context of native rust.
This mad man had the courage to present BOA a rust project at JS Conf. The project had it's spotlight taken by Bun and Deno. I also think the project was progressing pretty slowly from what people were expecting.
Readit News
I’m the creator of Boa, you can catch my talk about it at JS Conf EU 2019 https://www.youtube.com/watch?v=_uD2pijcSi4
That said, today Boa has a whole team of maintainers who I’m sure will answer some questions here.
Yes the name does invoke the sense it’s a Python project but I liked it and stuck with it, I saw a Boa snake at a zoo once and knew I wanted to name my next project after it, I was also inspired by Mozilla at the time who named their projects after animals.
Speaking of Mozilla, Boa’s existence came to be because at the time I was working on Servo and wanted to include an all-rust JS engine, one didn’t really exist so I set about making one as a learning exercise, after around 2 years more joined me on that journey and today Boa is around 8 years old. It is not browser grade (although at 94.12% it is more compliant than some browser engines) but that doesn’t matter, plenty of Rust projects have found good use for it as they find it easy to embed and use, so we’re happy.
One recent example is Biome who use it for their plugin infrastructure. https://github.com/biomejs/biome/pull/7300
Another recent thing which we’re very proud is seeing our implementation of Temporal be used in V8 and other engines, so we’re also helping the wider ecosystem and raising all ships! (More here: https://boajs.dev/blog/2025/09/24/temporal-release)
We do hope to improve performance over the next year or so, hopefully that answers some of the Qs here.
Top tier reasoning, literally makes me want to use it
Deleted Comment
In general, we are shifting more to performance now than conformance. We currently sit at around 94% conformance, so there's not really that much more to go conformance-wise. The remaining conformance gains are a couple of the newer specification features and Intl related features. Our current conformance can be found at https://boajs.dev/conformance.
Regarding performance, we are already making some gains, with hopefully more to come. The best example of this was probably the updates to script-bench-rs with our most recent release (which can be found at this commit https://github.com/khvzak/script-bench-rs/commit/d9635de77d2...). We still obviously have more to improve on, but we have already made some pretty steady progress from where we were.
EDIT: I forgot to answer your question about v8-jitless. Obviously in the future it would be nice to be able to be more competitive with v8-jitless, but at least for me, I'd just like to focus on improving the Boa overall.
We hope to wind down some of the conformance priority now and focus on performance, we need to work on a new GC, refactor some parts of the engine, and improve various areas.
The idea of a JIT has been raised and we’re not against it, but it’s not on our plans right now (because of the above), that being said there is an open discussion.
I also really enjoyed your earlier deep dive blog posts on implementation of Temporal, https://boajs.dev/blog/2025/06/15/temporal-impl-1
There's also a very lovely talk Cross-Engine Contributions at Scale: How newcomers accelerated Temporal and Upsert in SpiderMonkey, V8, and Boa that goes deep in depth in how technically Temporal was used across engines. https://www.youtube.com/watch?v=WieD_9BswAE
Hopefully, there will be more chances in the future for projects like temporal_rs. Beyond just temporal_rs, I think the Temporal integration in V8 and Kiesel was a good proof of concept for Rust based libraries over FFI using Diplomat.
I'm not aware of any plans to build node-like modules, but I think we have the basic support to potentially build them out ... but I could be overlooking or missing something. I'm not personally familiar with them. But defining and using a macro should hopefully be fairly straightforward in Rust with the macros from our latest release (https://boajs.dev/blog/2025/10/22/boa-release-21#boa_module). If we're missing something, feel free to let us know.
Any runtime functionality that has been implemented is available in `boa_runtime`. I've mentioned this elsewhere in the thread, but this crate is not a runtime itself (yet). Currently, it's a collection of runtime features like `console` and `fetch`.
Someone on our last release thread on Reddit (https://www.reddit.com/r/rust/comments/1odnore/boa_0210_rele...) mentioned adding Boa to Blitz, which I think would be interesting to see as well.
We're looking into the next release potentially being a v1.0, so maybe that option is a bit more possible after that release. But at the same time, I think Servo spends a decent amount of time maintaining the `mozjs` crate, so who knows.
I can't speak exactly for the other maintainers, but for me, I mostly enjoy working on Boa and Boa related things (I've spent the better part of the last year and a half on the temporal implementation). I think it would be cool to have a highly performant and conformant Rust JavaScript engine. So that's my goal :)
I could easily see something similar to MongoDB being birthed out of Boa. MongoDB uses v8 for querying.
https://github.com/boa-dev/boa/blob/6200e4b5eec1284b87e902c5...
The Boa constructor
edit: I'm here all week btw
We, the maintainers, could probably sit down some day and try to triage the failures into a documented txt file, but the overhead on that might make it hard to maintain for an open source project. Plus a large amount of the failures are just new specification features that nobody has implemented yet.
Seems like a nice team and project.
Just to note, Boa is an JavaScript engine / interpreter. We're not a runtime, but we do already have some runtime features implemented in the `boa_runtime` crate, but I don't believe that includes any sandboxing as of right now. It's not even a full fledged runtime ... yet (there's been some discussion about expanding it to a full fledged runtime if anyone has a general interest to work on it). For now, `boa_runtime` is just a collection of features for users to potentially use and if they'd like to implement more, then they are totally welcome to.
I wonder what they're doing that's so different than Boa.
My first thought was that this could be interesting for yt-dlp?
The alternative might be https://github.com/denoland/rusty_v8 but without needing C++ V8.
(this is the first I'm hearing of Boa)
It (mlua) would be more similar to rusty_v8.
I'm always on the lookout for embeddable JS engines.
How hard would it be to make Boa deterministic?
Like, with seeded randomness, etc.