tsconfig.esm.json

{
  // The second half of `npm run build`: the same sources, emitted as ES
  // modules into dist/esm.
  //
  // WHY A SECOND BUILD AT ALL. tsconfig.json says `"module": "commonjs"` and
  // tsconfig.build.json does not override it, so dist/ is CommonJS — which is
  // what Node's `require` and every `main`-resolving bundler want, and what
  // this package will keep shipping there. But a CommonJS barrel cannot be
  // tree-shaken per export: webpack, Rollup and Vite (the bundlers
  // scripts/emit-dist-spec-shim.mjs exists to serve, i.e. react-native-web)
  // can only drop a module nothing imports, so `sideEffects: false` on its own
  // left an app that imports `parseDocument` carrying the streaming, selection
  // and view layers as well. The `import` condition in package.json's
  // `exports` points at this output instead, and those bundlers can then drop
  // what the app does not reference.
  //
  // WHAT MAKES THE OUTPUT LOADABLE. tsc does not rewrite import specifiers, so
  // this emit alone would produce ES modules full of extensionless relative
  // imports that Node's ESM resolver rejects, in a directory Node reads as
  // CommonJS. scripts/finish-esm-build.mjs closes both: it writes
  // dist/esm/package.json (`"type": "module"`, and `sideEffects: false` again,
  // because a bundler reads the NEAREST package.json for that hint) and adds
  // the explicit `.js` extension every relative specifier needs. The build
  // fails if any specifier is left without one.
  //
  // "module": "es2020" rather than esnext so the emit cannot start using
  // syntax (import assertions, `import.meta` forms) that a consumer's older
  // bundler has never seen; the source targets es2020 everywhere else too.
  "extends": "./tsconfig.build.json",
  "compilerOptions": {
    "module": "es2020",
    "outDir": "dist/esm"
  }
}