fix(query-core): guard against undefined pages in hasNextPage/hasPreviousPage

[ZacharyL2]

Summary

hasNextPage / hasPreviousPage crash with TypeError: Cannot read properties of undefined (reading 'length') when state.data is a malformed InfiniteData whose pages is undefined.

The InfiniteData interface declares pages: Array<TData> as required, which is true for data produced by infiniteQueryBehavior's own fetch. But state.data can also be populated from outside that path — SSR hydration, a manual setQueryData, or a persisted/restored cache — where the object may not honor the type. When such data reaches getNextPageParam, the unconditional pages.length throws.

Notably, onFetch in the same file already anticipates this:

const oldPages = context.state.data?.pages || []
const oldPageParams = context.state.data?.pageParams || []

getNextPageParam / getPreviousPageParam / hasNextPage / hasPreviousPage simply didn't get the same defensive treatment. This PR makes them consistent.

Crash

TypeError: Cannot read properties of undefined (reading 'length')
  at getNextPageParam (infiniteQueryBehavior.ts) — const lastIndex = pages.length - 1
  at hasNextPage (infiniteQueryBehavior.ts)
  at InfiniteQueryObserver.createResult
  at InfiniteQueryObserver.updateResult
  ...

Seen in production on a TanStack Start (SSR) app across multiple infinite queries; intermittent, tied to hydration timing.

Change

• Type the data argument of getNextPageParam / getPreviousPageParam as Partial<InfiniteData<unknown>> to reflect that it can be malformed at runtime (no as casts).
• Guard if (!pages?.length) return undefined before indexing.
• When pages is a valid non-empty array the behavior is unchanged — pageParams ?? [] is a no-op on well-formed data, since pages and pageParams are always written together.

The result: a malformed pages now yields "no next/previous page" instead of throwing, so hasNextPage / hasPreviousPage return false.

Test

Added a regression test asserting hasNextPage / hasPreviousPage return false (instead of throwing) for malformed InfiniteData. It fails without this change.

Changeset

Included as a patch for @tanstack/query-core.

Summary by CodeRabbit

• Bug Fixes
  • Improved infinite query handling when stored data is incomplete or missing page information.
  • Prevented errors in “next” and “previous” page checks when page data is undefined, returning a safe result instead.
  • Added coverage for malformed infinite query data to ensure these checks behave reliably.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: d11d64cb-deed-491b-9376-fbc9b374af17

📥 Commits

Reviewing files that changed from the base of the PR and between 8d979da and 0891b35.

📒 Files selected for processing (3)

• .changeset/guard-infinite-undefined-pages.md
• packages/query-core/src/__tests__/infiniteQueryBehavior.test.tsx
• packages/query-core/src/infiniteQueryBehavior.ts

---

📝 Walkthrough

Walkthrough

Guards getNextPageParam and getPreviousPageParam in infiniteQueryBehavior.ts against malformed InfiniteData where pages is undefined, using optional chaining and a fallback empty array. A test verifies the helpers return false instead of throwing, and a changeset is added.

Changes

Infinite Query pages undefined guard

Layer / File(s)	Summary
Core guard in getNextPageParam / getPreviousPageParam packages/query-core/src/infiniteQueryBehavior.ts	Both helpers now destructure Partial<InfiniteData<unknown>>, guard with !pages?.length, and use pageParams ?? [] fallback, tolerating missing pages/pageParams.
Test and changeset packages/query-core/src/__tests__/infiniteQueryBehavior.test.tsx, .changeset/guard-infinite-undefined-pages.md	Imports hasNextPage/hasPreviousPage in the test file; adds a test case asserting both return false for malformed InfiniteData; changeset records the patch.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~5 minutes

Poem

🐇 When pages are missing, oh what a fright,
The query would crash in the dark of the night.
But now with a guard and a ?. in place,
We return a calm false with infinite grace.
No TypeError thrown — just a hop and a skip! 🌙

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers the change well, but it does not follow the required template and omits the checklist and release-impact sections.	Reformat it to the repo template and add the Checklist and Release Impact sections, including the appropriate checked boxes.
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly matches the main change: guarding hasNextPage/hasPreviousPage against undefined pages.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}