Falsy timer ID (0) prevents proper timeout/interval cleanup with custom timeout provider

[mukeshdhadhariya]

Describe the bug

When using a custom timeout provider, timer IDs can legally be 0. However, the codebase uses truthy checks before calling clearTimeout / clearInterval. Since 0 is falsy, timers with ID 0 are never cleared.

This leads to stale timers continuing to run, causing unexpected refetches, extra updates, and lifecycle inconsistencies.

---

Custom timeout provider that returns 0:

// Custom timeout provider
let firstTimeout = true
let firstInterval = true

const timeoutProvider = {
  setTimeout: (fn, ms) => {
    if (firstTimeout) {
      firstTimeout = false
      return 0
    }
    return window.setTimeout(fn, ms)
  },
  clearTimeout: (id) => {
    console.log('clearTimeout called with:', id)
    window.clearTimeout(id)
  },
  setInterval: (fn, ms) => {
    if (firstInterval) {
      firstInterval = false
      return 0
    }
    return window.setInterval(fn, ms)
  },
  clearInterval: (id) => {
    console.log('clearInterval called with:', id)
    window.clearInterval(id)
  }
}

Use this provider with QueryClient / QueryObserver and trigger cleanup (e.g., unsubscribe or option update). Timers with ID 0 will not be cleared.

---

Timers should always be cleared regardless of their numeric value. Even when the timer ID is 0, cleanup functions should be called:

clearTimeout(0)
clearInterval(0)

---

Actual behavior

Timers with ID 0 are not cleared because of truthy checks like:

if (this.#gcTimeout) {
  clearTimeout(this.#gcTimeout)
}

Since 0 is falsy, the cleanup logic is skipped.

---

Proposed fix

Replace truthy checks with explicit undefined checks:

// Before
if (this.#gcTimeout)

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

Apply similar fixes to:

• this.#staleTimeoutId
• this.#refetchIntervalId

Your minimal, reproducible example

Replace all truthy timer checks (e.g., if (timerId)) with explicit undefined checks (e.g., if (timerId !== undefined)) so timer ID 0 is handled correctly.

Steps to reproduce

1. Create a custom timeout provider where setTimeout or setInterval returns 0
2. Use it with QueryClient / QueryObserver
3. Configure staleTime or refetchInterval so timers are scheduled
4. Trigger cleanup (unsubscribe or update options)
5. Observe that clearTimeout / clearInterval are not called for ID 0

Expected behavior

Timers should always be cleared regardless of their numeric value. Even when the timer ID is 0, cleanup functions should be called:

clearTimeout(0)
clearInterval(0)

How often does this bug happen?

None

Screenshots or Videos

No response

Platform

• OS: Windows
• Browser: Chrome, Edge
• Runtime: Node.js

Tanstack Query adapter

None

TanStack Query version

5.96.2

TypeScript version

No response

Additional context

No response