ssr-noexternal-netlify

SSR noExternal for Netlify (Webflow → TanStack Start)

These crashes are runtime-only — npm run build and vite dev will not catch them. They surface on the first request to the deployed Netlify function.

When you see it

The Netlify function crash page shows one of:

• SyntaxError: Cannot use import statement outside a module with node:internal/modules/cjs/loader in the stack — Node tried to load an ESM-only file (e.g. node_modules/<pkg>/index.js) through the CommonJS loader.
• Error [ERR_REQUIRE_ESM]: require() of ES Module … — a CJS file inside a package called require() on an ESM-only sibling.
• Error: Cannot find module '<pkg>' with Require stack → server.mjs — Netlify did not trace a transitive dependency into the function bundle. Add <pkg> to ssr.noExternal (same as ESM fixes).

The first stack frame names the file: /var/task/node_modules/<pkg>/<file>. <pkg> is what you add.

Fix

In web/vite.config.ts:

export default defineConfig({
  ssr: {
    noExternal: [
      // Append the package name from the function stack trace.
      // Add transitive deps if subsequent crashes name them.
    ],
  },
  // …plugins
})

Vite then inlines the package into dist/server/assets/routes-*.js, so the Netlify function never reads the raw file and Node's CJS/ESM rules stop applying.

Local SSR smoke test (run after every change to the list)

cd web && npm run build && \
  node -e "import('./.netlify/v1/functions/server.mjs')\
    .then(() => console.log('SSR import OK'))\
    .catch(e => { console.error(e); process.exit(1) })"

If this prints SSR import OK, the same module graph will at least start on Netlify. Run it before every push that changes vite.config.ts, the route components, or the dependency graph.

Per-site discipline

The list is additive and per-site. Different Webflow exports pull in different deps; a fixed list copied between projects either misses the real offender or bloats the SSR bundle.