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CONTRIBUTING.md

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Contribute to emnapi

Please feel free to open an issue or PR anytime.

This doc will explain the structure of this project and some points need to note before contributing.

Packages

  • packages/emnapi (devDependencies)

    The main package of emnapi, including all Node-API implementation, emnapi C headers, CMake configurations, and the Emscripten JavaScript library build. We finally need to build a Emscripten JavaScript library file which is designed for being used in link time. The library file is not a regular JavaScript file, it may contain some macros wrapped in {{{ }}} only available in Emscripten, and can not use ES Module format. Fortunately, we can write ESM code during development and then build the final library file through TypeScript custom transformers those are also in this repo.

    For example, write the following source code:

    import { makeSetValue } from 'emscripten:parse-tools'

/** @__sig vp */
export function foo (result: number) {
  makeSetValue('result', 0, 0, 'i32')
}

    This will output:

    function _foo (result) {
  {{{ makeSetValue('result', 0, 0, 'i32') }}}
}
addToLibrary({
  foo: _foo,
  foo__sig: 'vp'
})

    It is powered by packages/rollup-plugin-emscripten-esm-library and packages/ts-transform-emscripten-esm-library.

    In addition, macros are also heavily used in packages/emnapi to match the Node.js source as much as possible.

    import { $CHECK_ARG, $CHECK_ENV_NOT_IN_GC } from '...'

/** @__sig ipip */
export function napi_create_int32 (env: napi_env, value: int32_t, result: Pointer<napi_value>): napi_status {
  const envObject: Env = $CHECK_ENV_NOT_IN_GC!(env)
  $CHECK_ARG!(envObject, result)
  // ...
}

    Macros are powered by packages/ts-transform-macro

  • packages/core (dependencies)

    This package is designed for using emnapi on non-Emscripten platform, it is a trasformed output of packages/emnapi by using packages/ts-transform-emscripten-parse-tools.

    For common WebAssembly loading case, we can't use the Emscripten JavaScript library file built in packages/emnapi package. We need to manually provide imported symbols to the second parameter of WebAssembly.instantiate, so this is the use case of this package.

  • packages/runtime (dependencies)

    Provide runtime implementation of napi_value / napi_handle_scope / napi_ref etc.

  • packages/node (dependencies)

    Some APIs make sense on Node.js only, such as napi_async_init, napi_async_destroy and napi_make_callback. This package provide native Node.js bindings for JavaScript implementation as bridge.

Environment Requirements

  • Node.js >= 16
  • npm >= 8
  • npm install -g node-gyp
  • Emscripten >= 3.1.9, EMSDK environment variable
  • wasi-sdk latest, WASI_SDK_PATH environment variable
  • CMake >= 3.13
  • ninja-build

Debugging

  • Run npm run build to build packages
  • Open packages/test/**/*.js
  • Add break points
  • Launch Launch Test VSCode launch configuration
  • Input UV_THREADPOOL_SIZE environment variable
  • Select target tripple