initial files

.github/workflows/ci.yml

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+name: Node.js Test
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    environment: CI
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          registry-url: https://registry.npmjs.org/
+      - run: npm ci
+      - run: npm install
+      - run: npm test

.gitignore

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+/node_modules/
+/.parcel-cache/
+*.DS_Store

.npmrc

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+save-exact = true

buildHelper.ts

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+import fs from 'node:fs/promises'
+import { dirname, join } from 'node:path'
+import { fileURLToPath } from 'node:url'
+import packageJson from './package.json' with { type: 'json' }
+import { fork, spawn } from 'node:child_process'
+
+type Opts = { type: string, tscArgs: string[], renameFileArgs: string[] }
+
+const optionsMap: Record<string, Opts> = {
+  esm: {
+    type: 'module',
+    tscArgs: ['--project', 'tsconfig.json', '--declaration'],
+    renameFileArgs: ['esm']
+  },
+  cjs: {
+    type: 'commonjs',
+    tscArgs: ['--project', 'tsconfig.cjs.json', '--declaration'],
+    renameFileArgs: ['cjs']
+  }
+}
+
+const __dirname = dirname(fileURLToPath(import.meta.url))
+
+const withTempTypeWrapper = async (newType: string, run: () => Promise<void> | void) => {
+  const suffix = crypto.randomUUID()
+  const tempFilePath = join(__dirname, `~$package.json.${suffix}`)
+  const packageJsonPath = join(__dirname, 'package.json')
+  await fs.copyFile(packageJsonPath, tempFilePath)
+  try {
+    const newContents = structuredClone(packageJson)
+    newContents.type = newType
+    await fs.writeFile(packageJsonPath, JSON.stringify(newContents, undefined, 2))
+    await run()
+  } finally {
+    await fs.copyFile(tempFilePath, packageJsonPath, fs.constants.COPYFILE_FICLONE)
+    await fs.unlink(tempFilePath)
+  }
+}
+
+const buildInternal = async (opts: Opts) => {
+  await new Promise<void>((resolve, reject) => {
+    const tsc = spawn('tsc', opts.tscArgs, {
+      env: {
+        ...process.env,
+        PATH: [join(__dirname, 'node_modules', '.bin'), process.env.PATH].filter(Boolean).join(':')
+      },
+      stdio: 'inherit'
+    })
+    tsc.on('close', (code) => {
+      if (code !== 0) {
+        reject(new Error(`[tsc] code ${code}`))
+      } else {
+        resolve()
+      }
+    })
+  })
+  await new Promise<void>((resolve, reject) => {
+    const rename = fork(new URL('./renameFiles.mjs', import.meta.url), opts.renameFileArgs, { stdio: 'inherit' })
+    rename.on('close', (code) => {
+      if (code !== 0) {
+        reject(new Error(`[rename] code ${code}`))
+      } else {
+        resolve()
+      }
+    })
+  })
+}
+
+const build = async (opts: Opts) => {
+  if (packageJson.type !== opts.type) {
+    return withTempTypeWrapper(opts.type, () => buildInternal(opts))
+  } else {
+    return buildInternal(opts)
+  }
+}
+
+if (process.argv[2] === 'esm') {
+  await build(optionsMap.esm)
+} else if (process.argv[2] === 'cjs') {
+  await build(optionsMap.cjs)
+} else {
+  console.error('Invalid build type')
+}