Better visibility of `async_local_storage_unavailable` error

[hyunbinseo]

Describe the bug

• Enable Async SSR
• Deploy to Cloudflare Pages (without nodejs_compat which is the default)

Above combination returns a generic 500 error page.

To see the actual error you are supposed to stream the logs for that deployment in the dashboard.

Since this is a blocking configuration error, it would be nice if:

• The message is shown in the error page
• A note is added to the await docs (since CF is an official adapter)
• A wrangler.json config is added when scaffolding with the adapter

"compatibility_flags": ["nodejs_compat"]

Also see

• wrangler.jsonc file not utilized in Cloudflare Pages build #14926

Reproduction

• https://github.com/hyunbinseo/svelte-kit-15029
• https://svelte-kit-15029.pages.dev/

Logs

{
  "message": [
    `[500] GET /pathname
      Svelte error: async_local_storage_unavailable
      The node API `AsyncLocalStorage` is not available, but is required to use async server rendering.
      https://svelte.dev/e/async_local_storage_unavailable
        at async_local_storage_unavailable (functionsWorker-0.22030710396640174.js:2069:18)
        at with_render_context (functionsWorker-0.22030710396640174.js:2125:7)
        at functionsWorker-0.22030710396640174.js:2759:25
        at async functionsWorker-0.22030710396640174.js:16122:70
        at async render_response (functionsWorker-0.22030710396640174.js:16111:18)
        at async respond_with_error (functionsWorker-0.22030710396640174.js:16596:12)
        at async render_page (functionsWorker-0.22030710396640174.js:17135:12)
        at async resolve22 (functionsWorker-0.22030710396640174.js:18383:25)
        at async Object.handle (functionsWorker-0.22030710396640174.js:5080:24)
        at async fn (functionsWorker-0.22030710396640174.js:18242:16)`
  ],
  "level": "error",
  "timestamp": 1764818209741
}

System Info

System:
  OS: Windows 11 10.0.26200
  CPU: (8) x64 Intel(R) Core(TM) Ultra 7 258V
  Memory: 11.78 GB / 31.48 GB
Binaries:
  Node: 24.11.0 - C:\Users\hyunb\AppData\Local\fnm_multishells\6880_1764897970479\node.EXE
  Yarn: 1.22.22 - C:\Users\hyunb\AppData\Local\fnm_multishells\6880_1764897970479\yarn.CMD
  npm: 11.6.1 - C:\Users\hyunb\AppData\Local\fnm_multishells\6880_1764897970479\npm.CMD
  pnpm: 10.24.0 - C:\Users\hyunb\AppData\Local\fnm_multishells\6880_1764897970479\pnpm.CMD
  Deno: 2.4.0 - C:\Users\hyunb\.deno\bin\deno.EXE
Browsers:
  Chrome: 143.0.7499.40
  Edge: Chromium (140.0.3485.54)
  Firefox: 145.0.2 - C:\Program Files\Mozilla Firefox\firefox.exe
npmPackages:
  @sveltejs/adapter-cloudflare: ^7.2.4 => 7.2.4
  @sveltejs/kit: ^2.48.5 => 2.49.1
  @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.1
  svelte: ^5.43.8 => 5.45.5
  vite: ^7.2.2 => 7.2.6

Severity

annoyance

Additional Information

No response

[elliott-with-the-longest-name-on-github]

I have been a bit confused about us not adding the nodejs compat flags by default, as they're... kind of required for SvelteKit (even without async) to work fully. I'm a little resistant to adding docs that basically say "You need standard node APIs to exist in order to use this", as that should just be the expectation, and the error does give you the exact information you need. I'm continually baffled that you have to manually turn a flag on to enable them on CF. I'd be less resistant to adding this documentation to the CF adapter. I might be able to be swayed either way, though. 😆

I'm not sure there's really anything we can/should do about the error page. These are server-side logs, and we wouldn't want to be piping any server-side content to the clientside on a production build. The best we could do here is maybe something along the lines of React, where we include some sort of digest you can use to search your logs on the server.