Skip to content

RFC: lean core JSC #836

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
Kudo merged 4 commits into from
Mar 5, 2025
Merged

RFC: lean core JSC #836

Changes from 1 commit
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
f28ea89
RFC: lean-core-jsc
Kudo Nov 28, 2024
f57bb73
Apply suggestions from code review
Kudo Jan 20, 2025
a88603c
Update proposals/0836-lean-core-jsc.md
cortinico Feb 7, 2025
a758c94
Update 0836-lean-core-jsc.md
Kudo Feb 27, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
33 changes: 33 additions & 0 deletions proposals/0836-lean-core-jsc.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
---
title: Extract JSC (JavaScriptCore) from React Native Core
author:
- Kudo Chien <[email protected]>
date: 2024-11-28
---

# RFC0836: Extract JSC (JavaScriptCore) from React Native Core

## Summary

This RFC proposes a Lean Core effort to extract JSC (JavaScriptCore) from React Native's core.

## Proposed Changes and Timeline

- Version 0.77: Remove the [`jsc-android` npm dependency](https://github.com/facebook/react-native/blob/2d337efc23c662143b3f39a6c994d80fec047054/packages/react-native/package.json#L132) from React Native and instead download the artifact from Maven Central. When using Hermes, downloading the unused npm dependency is unnecessary and removing it saves about 32 MB of uncompressed size.
Copy link

@NickGerleman NickGerleman Nov 29, 2024

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Is this needed in 0.77 for 16KB page support?

Copy link
Member Author

@Kudo Kudo Nov 29, 2024

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

yes, but if there's concern to cherry-pick facebook/react-native#47972 to 0.77. we can postpone the mavenCentral migration to 0.78. on 0.77 we still use jsc-android npm package for a newer version with android 16kb page support.

Copy link
Member

@cortinico cortinico Dec 4, 2024

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I'd rather go with 0.78.

Our take on 16K support is that it's Hermes first. Originally we were not even planning to include JSC for 16K support.

- Version 0.78 or 0.79: Introduce a new `react-native-javascriptcore` npm package with a newer version of JavaScriptCore for Android. In this version, we will only provide the [Intl variant](https://github.com/react-native-community/jsc-android-buildscripts/blob/9c61fece4753902a2cd6d29dfa46b7b521f0c821/README.md#international-variant), as newer JavaScriptCore versions do not support disabling Intl. The existing JSCRuntime from the core should still function with this version but will display a deprecation warning during build time. A challenge will be managing the core JSCRuntime alongside the third-party JSCRuntime from `react-native-javascriptcore`; further study is required.
- Version 0.80: Completely remove JavaScriptCore from the core:
- Eliminate `JSCRuntime` code.
- Deprecate Gradle's `hermesEnabled` and Podfile's `hermes_enabled`, making them no-ops.
- Update documentation at https://reactnative.dev/docs/hermes.

## Motivation

Since Hermes has become the dominant JavaScript engine in the React Native ecosystem, it is inefficient to include unused JavaScriptCore code and binaries in the core. By extracting JavaScriptCore to a separate, third-party maintained library, we can streamline the core and reduce unnecessary bloat.

## Adoption strategy

We will offer a drop-in replacement with the `react-native-javascriptcore` npm package while maintaining JSC support in the core for two additional React Native releases to ensure a smooth transition.
Copy link

@NickGerleman NickGerleman Nov 29, 2024

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

If the boundary is jsi::Runtime, then I think that means there could be frequent updates needed against RN package.

The current structure has a nice benefit of keeping it up to date automatically, since it must build in line with JSI changes. But I think it means the project would need a long term maintainer to continue working. See microsoft/v8-jsi@4438466

Depending on whether there is a natural maintainer, the other option would look like a harder deprecation, which would still allow externally maintained runtimes to develop.

Copy link
Member Author

@Kudo Kudo Nov 29, 2024

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

this is also the same problem for https://github.com/Kudo/react-native-v8. i can try to maintain the in my spare time (also love to have other maintainers from community)

maybe we need to include nightly testing from v8 and react-native-javascriptcore, so that we can catch jsi interface breaking changes and take action earlier.

Copy link
Member

@thymikee thymikee Nov 29, 2024

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We'd be happy to help with maintenance of that RN <-> JSC integration at Callstack

Copy link
Member Author

@Kudo Kudo Nov 30, 2024

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

awesome! love the collaboration with someone from Callstack then.


## How we teach this

We will announce the upcoming changes in the version 0.77 release notes and provide guidance for developers on migrating to the new `react-native-javascriptcore` package.