Initial pass at blog post for next release

Author: nekevss

blog/boa-release-21.md

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+---
+layout: post
+tags: [post]
+title: "Boa release v0.21"
+description: "Boa release v0.21"
+authors: boa-dev
+---
+
+## Summary
+
+Boa v0.21 is now available! After 9 months of development we are very
+happy to present you the latest release of the Boa JavaScript engine.
+Boa makes it easy to embed a JS engine in your projects, and you can
+even use it from WebAssembly. See the [about](/about) page for more
+info.
+
+In this release, our conformance has grown from 89.92% to 93.94% in the
+official ECMAScript Test Suite (Test262). Our growth in conformance is
+driven by increased conformance for Temporal (discussed further below)
+with the rest of the development effort being focused on performance and
+runtime features. We will continue to implement more of the
+specification; however, as of the current moment, Boa's conformance
+aligns with the major browser engine's conformance, so future increases
+in conformance will be minor or bound to the feature size going forward.
+
+You can check the full list of changes [here][changelog], and the full
+information on conformance [here][conformance].
+
+<!--truncate-->
+
+## Feature Highlights
+
+### Temporal
+
+There has been a lot of progress made on Temporal, the new Stage 3
+date/time proposal. With this release, Boa's conformance on Temporal
+grew from 40.67% to 97.06%. As of this moment, Boa is the second most
+conformant Temporal implementation behind SpiderMonkey with others soon
+to follow.
+
+The implementation is backed by the `temporal_rs` date/time Rust
+library, which we went over briefly in our June
+[blog post](./2025-06-15-temporal-impl-1.md) with hopefully another post
+in the not too distant future. So far, `temporal_rs` has been used in
+both V8 and Keisel to implement Temporal as well.
+
+Temporal can be used from `boa_cli` or enabled in `boa_engine` with the
+`experimental` or `temporal` feature.
+
+You can also try out Temporal directly in Rust using `temporal_rs`:
+
+```
+cargo add temporal_rs
+```
+
+#### Special thanks
+
+Special thanks to all the student's from University of Bergen as well as
+Shane Carr ([@sffc](https://github.com/@sffc)) and Manish Goregaokar
+([@manishearth](https://github.com/@manishearth)) from ICU4X for their
+contributions and help with `temporal_rs`.
+
+### New Set methods
+
+Boa now supports the new set methods added in ES2025.
+
+These new methods are:
+
+- `Set.prototype.intersection(other)`
+- `Set.prototype.union(other)`
+- `Set.prototype.difference(other)`
+- `Set.prototype.symmetricDifference(other)`
+- `Set.prototype.isSubsetOf(other)`
+- `Set.prototype.isSupersetOf(other)`
+- `Set.prototype.isDisjointFrom(other)`
+
+Thanks to [@Hemenguelbindi](https://github.com/@Hemenguelbindi) for
+their work on this feature.
+
+### Float16 support for TypedArrays, Dataview and Math built-ins
+
+Boa now supports `f16` types for the TypedArray, Dataview, and Math
+built-ins.
+
+```javascript
+const x = new Float16Array([37, 42]);
+console.log(x[1]); // 42
+```
+
+### Error.isError
+
+Boa now supports `Error.isError`, which is accepted for ES2026.
+
+```javascript
+let check = Error.isError(new Error()); // returns true
+```
+
+### Math.sumPrecise
+
+Boa now supports `Math.sumPrecise`, which is accepted for ES2026.
+
+```javascript
+let sum = Math.sumPrecise([1.0, 2.5]);
+console.log(sum); // 3.5
+```
+
+## Boa Runtime
+
+Work on Boa's runtime crate has continued with additional APIs added.
+
+### Additional APIs
+
+Additional APIs added the the Runtime crate include:
+
+- `fetch`
+- `setTimeout`
+- `setInterval`
+- `clearInterval`
+- `queueMicrotask`
+
+### Conformance testing
+
+We've added some support for conformance testing runtime features
+against the Web Platform Tests (WPT).
+
+## Performance
+
+### Register VM
+
+With this release, Boa's virtual machine (VM) moved from a stack based
+VM to a register based VM.
+
+## New Contributors
+
+TODO
+
+## Looking Forward
+
+### Garbage collector rewrite
+
+This has been long overdue. Boa's garbage collector is a forked and
+modified verison of `rust-gc`, and we have long been pushing our forked
+gc to its limits.
+
+We have seen plenty of evidence that simply swapping allocators can
+increase Boa's performance, and work on this will hopefully resume soon.
+If you're interested in garbage collectors and/or would be interested in
+helping out, feel free to join our GC room on [Matrix].
+
+### Runtime functionality
+
+The `boa_runtime` crate was initially meant to contain functionality
+that was not meant to exist in the core engine, primarily our console
+implementation. Noticeably, we have since added more runtime features to
+the crate with more expected in the next release.
+
+Our current plan is if there is enough interest and the crate becomes
+too large, we will split `boa_runtime` into it's own repository. If you
+are interested in implementing any runtime features, feel free to reach
+out.
+
+## How can you support Boa?
+
+Boa is an independent JavaScript engine implementing the ECMAScript
+specification, and we rely on the support of the community to keep it
+going. If you want to support us, you can do so by donating to our [open
+collective]. Proceeeds here go towards this very website, the domain
+name, and remunerating members of the team who have worked on the
+features released.
+
+If financial contribution is not your strength, you can contribute by
+asking to be assigned to one of our [open issues], and asking for
+mentoring if you don't know your way around the engine. Our
+[contribution guide] should help you here. If you are more used to
+working with JavaScript or frontend web development, we also welcome
+help to improve our web presence, either in [our website], or in our
+[testing representation] page or benchmarks page. You can also
+contribute to our Criterion benchmark comparison GitHub [action].
+
+We are also looking to improve the documentation of the engine, both for
+developers of the engine itself and for users of the engine. Feel free
+to contact us in [Matrix].
+
+[open collective]: https://opencollective.com/boa
+[open issues]:
+  https://github.com/boa-dev/boa/issues?q=is%3Aopen+is%3Aissue+no%3Aassignee
+[contribution guide]:
+  https://github.com/boa-dev/boa/blob/main/CONTRIBUTING.md
+[our website]: https://github.com/boa-dev/boa-dev.github.io
+[testing representation]: https://github.com/boa-dev/boa/issues/820
+[action]: https://github.com/boa-dev/criterion-compare-action
+[Matrix]: https://matrix.to/#/#boa:matrix.org
+
+## Thank You
+
+Once again, big thanks to [all the contributors][contributors] of this
+release!!!
+
+[contributors]:
+  https://github.com/boa-dev/boa/graphs/contributors?from=2024-12-05&to=2025-08-30&type=c
+[changelog]: https://github.com/boa-dev/boa/blob/v0.21/CHANGELOG.md
+[conformance]: https://boajs.dev/boa/test262/
+[feed]: https://boajs.dev/blog/rss.xml
+[collective]: https://opencollective.com/boa
+[easy_issues]:
+  https://github.com/boa-dev/boa/issues?q=is%3Aopen+is%3Aissue+label%3AE-Easy
+[first_issues]:
+  https://github.com/boa-dev/boa/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22