Warning after upgrading to Nuxt 3.17.x: useAsyncData must return a value
Hey everyone! 👋 I’m using Nuxt
3.17.5 together with @nuxt/content 3.6.3.
After upgrading Nuxt to 3.17.6 (or 3.17.7), I started seeing this warning in the console:
The thing is, my code follows exactly the same pattern as the official example from the docs:
https://content.nuxt.com/docs/utils/query-collection#usage
Here’s the snippet I’m using:
This was working fine before the upgrade.
Any idea why this warning is appearing now? Is there something that changed in how useAsyncData or @nuxt/content should be used?
Thanks in advance! 🙏5 Replies
Hi @Andrzej. I'm kapa.ai, your friendly support bot. I will try to answer your question by searching through the knowledge base. :wave:
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The warning you’re seeing:
is related to a change in how Nuxt 3.17.x handles the return value of the handler function in useAsyncData. In recent versions, Nuxt expects your handler to always return a value that is not undefined (and, in Nuxt 3, not null either). If your handler returns undefined or null, Nuxt may trigger a second fetch on the client side, leading to this warning.
This behavior is confirmed in the Nuxt issue tracker: returning null or undefined from useAsyncData’s handler will trigger this warning and may cause a duplicated client-side fetch. In Nuxt 3, only upgrading to Nuxt 4 will allow returning null without this side effect; the compatibility flag does not change this in Nuxt 3. The warning message was updated for clarity, but the underlying behavior remains: you must return a defined value from your handler in Nuxt 3.17.x and above Warning for undefined/null in useAsyncData.
What changed?
- In Nuxt 3.17.x, the data fetching system was reorganized for consistency and performance. Now, all calls to useAsyncData with the same key share the same refs, and stricter checks are in place for handler return values Singleton Data Fetching Layer.
- The warning is triggered if your handler returns undefined or null, which can happen if queryCollection(...).first() does not find a matching document and returns undefined.
How to fix?
- Ensure your handler always returns a defined value. For example, provide a fallback:
or use a default value that makes sense for your use case.
Summary:
This warning is expected in Nuxt 3.17.x if your handler can return undefined or null. To resolve it, always return a defined value from your useAsyncData handler. This is a change from previous versions and is now required for correct SSR/client hydration behavior Warning for undefined/null in useAsyncData. ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------
This warning is expected in Nuxt 3.17.x if your handler can return undefined or null. To resolve it, always return a defined value from your useAsyncData handler. This is a change from previous versions and is now required for correct SSR/client hydration behavior Warning for undefined/null in useAsyncData. ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------
<@1211943824205815869> Kapa.ai is still learning and improving, please let me know how I did by reacting below.
While returning a fallback value (like
[] or {}) works to silence the warning, it feels a bit off — since useAsyncData is designed to handle async resolution, it seems like it should be able to deal with undefined results as well.
If the intention is to defer the fetch and avoid hydration mismatches, I’d probably lean towards using useLazyAsyncData instead, as it better fits that behavior. But I understand now that with the new stricter checks in Nuxt 3.17, returning undefined is no longer acceptable even in cases where it previously worked...it is resolved in v4 as it is a breaking change
the warning is accurate though. previously it didn't warn but the data would have been refetched
Ok, got it — fair enough. Thanks for stopping by 🙇♂️