fix: read version-specific h3 exports via runtime key

package.json

@@ -77,6 +77,7 @@
     "node-fetch-native": "^1.4.0",
     "pnpm": "^8.7.0",
     "rimraf": "^5.0.1",
+    "rollup": "3.28.1",
     "simple-git-hooks": "^2.9.0",
     "supertest": "^6.3.3",
     "typescript": "^5.2.2",

src/helper.ts

@@ -17,13 +17,18 @@ export type Compression = 'gzip' | 'deflate' | 'br'
 export type StreamCompression = 'gzip' | 'deflate'
 
 /**
- * `send` was removed and `toResponse` was added in h3 v2. They are accessed
- * dynamically so this package keeps working with both h3 v1 and v2.
+ * `send` (h3 v1) and `toResponse` (h3 v2) each only exist in a single major
+ * version. They are read through a runtime key so that bundlers (Nuxt / Nitro /
+ * Rollup re-bundling `dist/index.mjs`) don't turn the namespace member access
+ * into a static `import { toResponse } from 'h3'`, which would fail on the other
+ * version (see issue: Nuxt build error `"toResponse" is not exported by h3`).
  */
-const send = (h3 as { send?: (event: H3Event, data?: unknown) => unknown }).send
-const toResponse = (h3 as {
-  toResponse?: (val: unknown, event: H3Event) => Response | Promise<Response>
-}).toResponse
+function h3Export<T>(name: string): T | undefined {
+  return (h3 as Record<string, unknown>)[name] as T | undefined
+}
+
+const send = h3Export<(event: H3Event, data?: unknown) => unknown>('send')
+const toResponse = h3Export<(val: unknown, event: H3Event) => Response | Promise<Response>>('toResponse')
 
 /**
  * Returns the best compression accepted by the client via the

test/dist-bundling.test.ts

@@ -0,0 +1,67 @@
+import { execSync } from 'node:child_process'
+import { existsSync } from 'node:fs'
+import { fileURLToPath } from 'node:url'
+import { dirname, resolve } from 'node:path'
+import { beforeAll, describe, expect, it } from 'vitest'
+
+const root = resolve(dirname(fileURLToPath(import.meta.url)), '..')
+const distEntry = resolve(root, 'dist/index.mjs')
+
+/**
+ * A stub for `h3` that mimics how a single h3 major looks to a bundler: it
+ * exports the symbols that exist in *both* versions, but never both `send`
+ * (v1 only) and `toResponse` (v2 only). If the package forces a static named
+ * import of a version-specific symbol, Rollup re-bundling `dist/index.mjs`
+ * (as Nuxt / Nitro does) emits a `MISSING_EXPORT` warning — exactly the
+ * `"toResponse" is not exported by h3` build error reported downstream.
+ */
+const h3Stub = `
+export const getRequestHeader = () => undefined
+export const setResponseHeader = () => undefined
+`
+
+function stubPlugin() {
+  return {
+    name: 'h3-stub',
+    resolveId(id: string) {
+      if (id === 'h3')
+        return '\0h3-stub'
+      if (id.startsWith('node:'))
+        return { id, external: true }
+      return null
+    },
+    load(id: string) {
+      if (id === '\0h3-stub')
+        return h3Stub
+      return null
+    },
+  }
+}
+
+describe('downstream bundling (regression for #14 follow-up)', () => {
+  beforeAll(() => {
+    if (!existsSync(distEntry))
+      execSync('pnpm build', { cwd: root, stdio: 'inherit' })
+  }, 120_000)
+
+  it('bundles dist/index.mjs without missing h3 exports (v1 + v2 safe)', async () => {
+    const { rollup } = await import('rollup')
+
+    const warnings: string[] = []
+    const bundle = await rollup({
+      input: distEntry,
+      plugins: [stubPlugin() as any],
+      onwarn(warning) {
+        warnings.push(typeof warning === 'string' ? warning : warning.message)
+      },
+    })
+    await bundle.generate({ format: 'es' })
+    await bundle.close()
+
+    const missingExport = warnings.filter(
+      w => /is not exported by/.test(w) || /toResponse|"send"/.test(w),
+    )
+
+    expect(missingExport).toEqual([])
+  })
+})