[browser][coreCLR] Skeleton for JavaScript host

[pavelsavara]

Skeleton for JavaScript host

The goal on this PR is to establish directory structure and naming.

All new *.js files are

• hand written skeleton and PoC for now.
• It will be replaced by TypeScript sources in better quality in next PRs.
• later most of them would be generated into artifacts\obj
  • like artifacts\obj\native\<RID>\System.Native.Browser\ next to libSystem.Native.Browser.a

Functionality

As compared to current WASM corerun, this could run in a browser as well as in NodeJS.
In NodeJS it expects all managed assemblies in the current folder and name of main assembly as first argument.
In browser, it loads assets as defined in dotnet.boot.js, which you can edit before you host it with dotnet-serve
The assemblies are loaded asynchronously and put into memory via external_assembly_probe callback.
All of this would be further integrated with existing Mono WASM SDK later.

New files

• src\native\corehost\browserhost\
  • this is targeting NodeJS for now
  • libBrowserHost.js - implements external_assembly_probe callback
  • browserhost.cpp - creates coreCLR instance
    • statically linked
    • no path probing or host policy
    • passing TRUSTED_PLATFORM_ASSEMBLIES as env var for the PoC, to be improved.
  • sample files
    • At the moment clumsy and to be simplified.
    • index.html - target web page
    • main.mjs - this is demo of the NodeJS usage.
    • dotnet.boot.js - list of assets to download. This going to be generated by MSBuild of the WASM SDK later. It's 100% compatible with Mono/Blazor
  • loader
    • ES6 JavaScript module representing public JS API and a loader/host
    • it will produce dotnet.js file in the final product.
    • the module downloads other JS modules, DLLs and other assets.
    • needs to be small so that it would start the download cascade quickly
• src\native\libs\Common\JavaScript
  • shared type definitions and small helpers connecting our JavaScript modules
• src\native\libs\System.Native.Browser\
  • Emscripten library with native functions for runtime PAL and ICalls
  • libSystem.Native.Browser.js - JS part of the library
  • libSystem.Native.Browser.extpost.js - ES6 exports helpers
  • CMakeLists.txt, entrypoints.c - native part of the library. C exports for P/Invoke.
• src\native\libs\System.Runtime.InteropServices.JavaScript.Native\
  • Emscripten library with native functions for JS interop
  • libSystem.Runtime.InteropServices.JavaScript.Native.js - JS part of the library
  • CMakeLists.txt, entrypoints.c - native part of the library. C exports for P/Invoke.
  • dotnet.runtime.js
    • ES6 JavaScript module with the JS interop marshallers
    • it will produce dotnet.runtime.js file in the final product.
• src\native\
  • root of the JavaScript build
  • package.json, package-lock.json, .npmrc - npm package definition and dependencies
  • .eslintrc.cjs, .eslintrc.cjs - JS code style
  • rollup.config.js - JS bundler and build script for TypeScript
  • tsconfig.json - typescript configuration

Q & A

• Q: does this support C code trimming
• A: not yet, until we generate list of P/Invoke dependencies from IL trimmed assemblies
• Q: does this support JS code trimming and symbol minifications
• A: It would (to some degree) once we bring TS. Protecting symbols from Emscripten is complex topic.
• Q: there are similar files in src\mono\browser\runtime, are we going to reuse them ?
• A: we are going to reuse best ideas, but keep Mono code as is in place
• Q: could we produce runtime without JavaScript interop assembly ?
• A: Tentative yes. I'm working on it. The challenge is that async C# Main() needs to yield to browser event loop and marshal Task/Promise. Synchronous main is not very useful in JS.

Fixes#119685
Contributes to #113067

[pavelsavara]

Together with #119591

[Copilot]

Pull Request Overview

Establishes the initial skeleton, layout, and build hooks for a JavaScript-based host for CoreCLR targeting browsers and NodeJS, plus supporting JS/TS library scaffolding.

• Introduces placeholder JS libraries for System.JavaScript and System.Runtime.InteropServices.JavaScript and wires them into the Emscripten build.
• Adds a simple browser/NodeJS host (C++ + JS glue) and pipeline/build file updates to include the new components.
• Provides initial TypeScript config, linting setup, and documentation placeholders for the upcoming TS-based implementation.

Reviewed Changes

Copilot reviewed 42 out of 48 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
src/native/libs/tsconfig.json	Adds TypeScript compiler configuration for JS/TS libraries.
src/native/libs/rollup.config.js	Placeholder rollup config; currently throws not-implemented (build stub).
src/native/libs/package.json	Adds npm metadata and devDependencies for rollup/TS/eslint build tooling.
src/native/libs/System.Runtime.InteropServices.JavaScript/libSystem.Runtime.InteropServices.JavaScript.js	Dummy JS interop library for Emscripten; exports interop entrypoints and initialization hooks.
src/native/libs/System.Runtime.InteropServices.JavaScript/entrypoints.c	C entrypoints mapping to JS implementations for P/Invoke resolution.
src/native/libs/System.Runtime.InteropServices.JavaScript/ReadMe.md	Documentation stub for the interop library.
src/native/libs/System.Runtime.InteropServices.JavaScript/CMakeLists.txt	CMake target for the native static library (conditional on GEN_PINVOKE).
src/native/libs/System.JavaScript/libSystem.JavaScript.js	Dummy PAL library functions (e.g., random bytes) and Emscripten integration.
src/native/libs/System.JavaScript/libSystem.JavaScript.extpost.js	Post-JS module to expose initialize entrypoint and create the Emscripten runtime.
src/native/libs/System.JavaScript/entrypoints.c	C entrypoints mapping to JS PAL functions for P/Invoke resolution.
src/native/libs/System.JavaScript/ReadMe.md	Documentation stub for the System.JavaScript PAL library.
src/native/libs/System.JavaScript/CMakeLists.txt	CMake target for System.JavaScript static lib and temporary JS asset installation.
src/native/libs/System.JavaScript.Runtime/dotnet.runtime.js	Minimal placeholder runtime JS module to satisfy build.
src/native/libs/System.JavaScript.Runtime/ReadMe.md	Documentation stub for the runtime module.
src/native/libs/System.JavaScript.Loader/dotnet.js	Loader/host ES module orchestrating runtime/wasm and assembly loading for browser/NodeJS.
src/native/libs/System.JavaScript.Loader/ReadMe.md	Documentation stub for the loader module.
src/native/libs/Common/JavaScript/types/index.ts	Barrel for shared type definitions.
src/native/libs/Common/JavaScript/types/emscripten.ts	Type definitions for Emscripten Module and pointers.
src/native/libs/Common/JavaScript/common/index.ts	Placeholder for shared helpers.
src/native/libs/Common/JavaScript/ReadMe.md	Documentation for shared types/helpers.
src/native/libs/CMakeLists.txt	Includes new JS libs for browser target builds.
src/native/libs/.eslintrc.cjs	ESLint configuration for TS/JS.
src/native/libs/.eslintignore	Ignore generated and JS files for linting.
src/native/corehost/browser/native.rc	Windows resource file for host.
src/native/corehost/browser/main.mjs	Simple NodeJS/browser host entrypoint (demo).
src/native/corehost/browser/libBrowserHost.js	Emscripten library exposing browser host callbacks and initializing DOTNET/interop.
src/native/corehost/browser/index.html	Minimal HTML for browser demo.
src/native/corehost/browser/dotnet.boot.js	Demo asset manifest for browser boot.
src/native/corehost/browser/configure.cmake	Configure checks and generated config header.
src/native/corehost/browser/config.h.in	Generated config header template.
src/native/corehost/browser/browserhost.cpp	CoreCLR bootstrapper using host runtime contract for JS/browser scenario.
src/native/corehost/browser/CMakeLists.txt	CMake target for browserhost, linking JS libraries and setting emscripten flags.
src/installer/pkg/sfx/Microsoft.NETCore.App/Directory.Build.props	Adds new native libs to platform manifest.
src/coreclr/vm/wasm/helpers.cpp	Removes temporary stub now provided by JS PAL.
src/coreclr/vm/CMakeLists.txt	Adds include paths for new JS libs on browser builds.
src/coreclr/hosts/corewasmrun/CMakeLists.txt	Links System.JavaScript lib into corewasmrun.
src/coreclr/hosts/corerun/libCorerun.pre.js	Pre-run script to copy Node env vars into Emscripten ENV.
src/coreclr/hosts/corerun/corerun.js	Removes old pre-js; replaced by libCorerun.pre.js.
src/coreclr/hosts/corerun/CMakeLists.txt	Wires new pre-js and System.JavaScript lib when targeting browser.
src/coreclr/CMakeLists.txt	Adds browserhost build and dependency for browser target.
eng/pipelines/common/evaluate-default-paths.yml	Ensures CI path filters include new JS/browser-host folders.
docs/workflow/building/coreclr/wasm.md	Adds VS Code NodeJS launch config for browserhost demo.

[pavelsavara]

This is ready for initial feedback.
The feedback I'm seeking is directory structure and naming.
The PR also has new summary in top description.

I'm also working on much nicer TypeScript version, but it needs more of my work.

[kg]

The parts I understand look pretty good.