A V8 adapter implemention of the JSI interface for the react-native framework.

1. Download and Install
   Windows 10 Windows SDK:
   https://developer.microsoft.com/en-us/windows/downloads/sdk-archive
   Note: Windows SDK has to be Windows 10 version, NOT Windows 11
2. Download and Install
   Microsoft Visual C++ Redistributable x64
   Microsoft Visual C++ Redistributable x86
   https://learn.microsoft.com/en-us/cpp/windows/latest-supported-vc-redist
3. Download and Install
   Visual Studio 2022
   https://visualstudio.microsoft.com/vs
   In Visual Studio Setup, Select the following Individual Components:
   • MSVC v143 - VS 2022 C++ x64/x86 Spectre-mitigated libs (Latest)
   • C++ ATL for latest v143 build tools with Spectre Mitigations (x86 & x64)
4. Enable PowerShell script execution
   Launch Cmd as Administrator

   powershell Set-ExecutionPolicy RemoteSigned

5. Perform Initial Build
   Launch Cmd as Standard user, NOT Administrator
   From V8-Jsi Repo directory:

   powershell ./localbuild.ps1
   

To build Win32 X64 Debug:

Launch Cmd as Standard user, NOT Administrator
From V8-Jsi Repo Directory:

powershell ./localbuild.ps1 -NoSetup

To build the specific platform and flavor, use appropriate build flags:

powershell ./localbuild.ps1 -NoSetup -Platform x86 -Configuration Release 

A second build path is being developed that compiles v8jsi.dll from a vendored copy of Node.js (under deps/nodejs/) without depot_tools / gclient. It produces its own v8jsi.dll, v8jsi_test.exe, and node_api_tests.exe into deps/nodejs/out/{Release,Debug}/ — the legacy build's outputs in out/{Release,Debug}/ are unaffected and continue to be the canonical artifacts shipped in the ReactNative.V8Jsi.Windows NuGet today.

The two builds will coexist until downstream consumers migrate to the new Microsoft.JavaScript.V8 NuGet, at which point the legacy build above is removed.

In addition to the prerequisites listed under Initial Windows Build Setup, the new build also needs:

1. Python 3.x on PATH (required by the Node.js configure step).
2. Node.js v24+ on PATH (required by scripts/build.ts).

dev.ps1 at the repo root is the canonical entry point for the new build. Run .\dev with no arguments to see available commands.

Build (Release x64 by default):

.\dev build

Other configurations:

.\dev build --configuration debug
.\dev build --platform x86
.\dev build --platform arm64

Build + run tests:

.\dev build --test

Run the fork-sync tool (sync vendored Node.js / asio from upstream):

.\dev fork-sync --dep nodejs --status

See .\dev build --help and .\dev fork-sync --help for the full option set. The build command forwards to scripts/build.ts, which drives deps/nodejs/vcbuild.bat with narrow-build flags (skips node.exe, cctest, embedtest, etc.). See CLAUDE.md for the underlying details.

.\dev build also runs a version-sync check that compares config.json.nodejs_version against the vendored Node.js version in deps/nodejs/src/node_version.h, and fails fast on mismatch. See docs/versioning.md for the 24.x.y policy.

• Enable Windows Subsystem for Linux
• Install debian: wsl --install -d Debian
• Install PowerShell in the Debian VM
• Install minimal dependencies on the Debian VM: sudo apt install lsb-release
• Make sure you have at least 15Gb of disk space on the drive where the WSL image lives (usually C:)
• Build with pwsh ./localbuild.ps1 -AppPlatform android
• If setup is completed successfully, build incrementally with pwsh ./localbuild.ps1 -AppPlatform android -NoSetup

• Install PowerShell by running brew install --cask powershell
• Build with pwsh ./localbuild.ps1 -AppPlatform mac
• If setup is completed successfully, build incrementally with pwsh ./localbuild.ps1 -AppPlatform mac -NoSetup
• Note: there are several test failures on macOS currently

Until the JSI headers find a more suitable home, they're currently duplicated between the various repos. Code in jsi\jsi should be synchronized with the matching version of JSI from react-native (from https://github.com/facebook/hermes/tree/master/API/jsi/jsi).

To regenerate after manual fix-ups, run:

• git diff --output=..\..\..\scripts\patch\build.diff --ignore-cr-at-eol from \build\v8\build\.
• git diff --output=..\..\scripts\patch\src.diff --ignore-cr-at-eol from \build\v8\.
• git diff --output=..\..\..\..\scripts\patch\zlib.diff --ignore-cr-at-eol from \build\v8\third_party\zlib\.

See Contributing guidelines for how to setup your fork of the repo and start a PR to contribute to React Native V8 JSI adapter.

The V8 JSI adapter, and all newly contributed code is provided under the MIT License. Portions of the JSI interface derived from Hermes are copyright Facebook.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.