fix(query-core): use !== undefined for timer ID checks to handle falsy 0 by ljjunh · Pull Request #10402 · TanStack/query

ljjunh · 2026-04-06T06:57:49Z

🎯 Changes

Timer IDs can legally be 0 when using a custom timeout provider. The current code uses truthy checks (if (this.#gcTimeout)) before calling clearTimeout/clearInterval, which silently skips cleanup when the ID is 0 since
0 is falsy in JavaScript.

Three locations were affected:

File	Method	Field
`removable.ts`	`clearGcTimeout()`	`#gcTimeout`
`queryObserver.ts`	`#clearStaleTimeout()`	`#staleTimeoutId`
`queryObserver.ts`	`#clearRefetchInterval()`	`#refetchIntervalId`

Replace truthy checks with explicit !== undefined comparisons:

// Before                                                                                                               
if (this.#gcTimeout) { ... }
                                                                                                                        
// After                                                  
if (this.#gcTimeout !== undefined) { ... }

## ✅ Checklist

- [x] I have followed the steps in the [Contributing guide](https://github.com/TanStack/query/blob/main/CONTRIBUTING.md).
- [x] I have tested this code locally with `pnpm run test:pr`.

## 🚀 Release Impact

- [x] This change affects published code, and I have generated a [changeset](https://github.com/changesets/changesets/blob/main/docs/adding-a-changeset.md).
- [ ] This change is docs/CI/dev-only (no release).


<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

* **Bug Fixes**
* Fixed timeout clearing mechanism to properly handle falsy timer identifiers (e.g., ID `0`) during cleanup operations.

* **Tests**
* Added test coverage for falsy timer ID handling in query observation and interval management.
* Added test suite for garbage collection timer cleanup with falsy timer IDs.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

coderabbitai · 2026-04-06T06:58:08Z

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The pull request is closed.

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Reviewing files that changed from the base of the PR and between ef887c9 and 3450e7d.

📒 Files selected for processing (1)

packages/query-core/src/__tests__/queryObserver.test.tsx

📝 Walkthrough

Walkthrough

Adds test coverage and a changeset entry for a bug fix addressing incorrect timer cleanup when custom timeout providers return falsy timer IDs (e.g., 0). The fix changes truthy checks to explicit undefined comparisons, ensuring falsy timer IDs are properly cleared during cleanup operations.

Changes

Cohort / File(s)	Summary
Changeset Entry `.changeset/seven-facts-unite.md`	Documents patch release with fix for `clearGcTimeout` using `!== undefined` check instead of truthy check to handle falsy timer IDs correctly.
QueryObserver Tests `packages/query-core/src/__tests__/queryObserver.test.tsx`	Adds two tests verifying falsy timer ID (`0`) handling: one for `setOptions` clearing timeout with ID `0`, another for `unsubscribe` clearing interval with ID `0`.
Garbage Collection Timer Tests `packages/query-core/src/__tests__/removable.test.tsx`	New test file verifying that garbage-collection timeout with falsy ID (`0`) is properly cleared when adding observers after subscription/unsubscription cycle.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

fix(query-core): clear timers when timer ID is 0 #10401 — Addresses the same underlying bug ensuring timer IDs of 0 are correctly cleared by modifying timer-clear logic in removable.ts and queryObserver.ts.

Poem

🐰 A timer that's zero won't hide anymore,
We check what is undefined, not what's falsy before,
With tests that verify each cleanup flow,
Those missing clears will surely go! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: replacing truthy timer checks with explicit !== undefined comparisons to handle falsy timer ID 0.
Description check	✅ Passed	The description follows the template with all required sections completed: changes clearly described with context and affected locations, checklist items checked, and release impact noted.
Linked Issues check	✅ Passed	All code changes address the requirements in issue `#10395`: replacements made in removable.ts, queryObserver.ts (both clearStaleTimeout and clearRefetchInterval), comprehensive tests added, and changeset created.
Out of Scope Changes check	✅ Passed	All changes are directly in scope: timer ID comparisons fixed in three locations, corresponding tests added to verify falsy ID 0 handling, and changeset documentation created.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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🧹 Nitpick comments (1)

.changeset/seven-facts-unite.md (1)

5-6: Changeset description is incomplete.

The description only mentions clearGcTimeout, but the fix also applies to #clearStaleTimeout and #clearRefetchInterval in queryObserver.ts. Consider updating for accurate release notes.

📝 Suggested changeset description

-fix: use !== undefined instead of truthy check for timer IDs to correctly handle falsy value 0 in clearGcTimeout,  
+fix: use !== undefined instead of truthy check for timer IDs to correctly handle falsy value 0 in clearGcTimeout, clearStaleTimeout, and clearRefetchInterval

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In @.changeset/seven-facts-unite.md around lines 5 - 6, Update the changeset
description in .changeset/seven-facts-unite.md to accurately reflect that the
fix replaces truthy checks with explicit !== undefined checks not only in
clearGcTimeout but also in `#clearStaleTimeout` and `#clearRefetchInterval` inside
queryObserver.ts; mention all three methods so release notes correctly state
that timer IDs with falsy value 0 are now handled properly.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In @.changeset/seven-facts-unite.md:
- Around line 5-6: Update the changeset description in
.changeset/seven-facts-unite.md to accurately reflect that the fix replaces
truthy checks with explicit !== undefined checks not only in clearGcTimeout but
also in `#clearStaleTimeout` and `#clearRefetchInterval` inside queryObserver.ts;
mention all three methods so release notes correctly state that timer IDs with
falsy value 0 are now handled properly.

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 87fe1f68-ef84-4589-817e-46877d8104b1

📥 Commits

Reviewing files that changed from the base of the PR and between eac62b8 and ef887c9.

📒 Files selected for processing (5)

.changeset/seven-facts-unite.md
packages/query-core/src/__tests__/queryObserver.test.tsx
packages/query-core/src/__tests__/removable.test.tsx
packages/query-core/src/queryObserver.ts
packages/query-core/src/removable.ts

TkDodo · 2026-04-09T07:40:53Z

i merged the other PR that did this.

fix(query-core): use !== undefined for timer ID checks to handle falsy 0

ef887c9

github-actions bot added the package: query-core label Apr 6, 2026

coderabbitai bot reviewed Apr 6, 2026

View reviewed changes

Merge branch 'main' into fix/falsy-timer-id-zero-not-cleared

3450e7d

TkDodo closed this Apr 9, 2026

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fix(query-core): use !== undefined for timer ID checks to handle falsy 0#10402

fix(query-core): use !== undefined for timer ID checks to handle falsy 0#10402
ljjunh wants to merge 2 commits intoTanStack:mainfrom
ljjunh:fix/falsy-timer-id-zero-not-cleared

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