TanStack
Function passed to `notifyOnChangeProps` cannot return `undefined`
Describe the bug
Background
notifyOnChangeProps is a query option that determines if the query should notify listeners if query properties change. It has the following type: https://github.com/TanStack/query/blob/1d60d44ad851472d37aaa3eef22ada07e5245989/packages/query-core/src/types.ts#L144-L148
Depending on the value set, it has the following behaviours:
-
undefined: The query will track which properties are accessed and only notify listeners if those properties change. This is the default option. -
string[]: The query will notify listeners if any of the properties in the array change. -
'all': The query will notify listeners if any properties change.
It can also be set with a function with the signature () => string[] | 'all'. The query will run the function and follow the behaviour listed above that matches the returned value.
With the available non-function options of undefined, string[], or 'all', it follows that the function should also be able to return undefined. However, the current type signature does not allow it.
Real world example
One real world example of the function passed to notifyOnChangeProps returning undefined comes from React Query's documentation itself, for disabling re-renders on out of focus screens on React Native. See this TypeScript Playground for a reproduction.
Impact
Allowing the function passed to notifyOnChangeProps to return undefined should not have any negative impact. At runtime, the query observer sets the value of notifyOnChangeProps or the value of the call to notifyOnChangeProps if it was a function to the same variable. This means if undefined is a valid value for notifyOnChangeProps then a call to notifyOnChangeProps should also be allowed to be undefined. See: https://github.com/TanStack/query/blob/1d60d44ad851472d37aaa3eef22ada07e5245989/packages/query-core/src/queryObserver.ts#L612-L616
Your minimal, reproducible example
https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBAbzgVwM4FMCKz1QJ5wC+cAZlBCHAOQACMAhgHaoMDGA1gPRTr2swBaAI458VAFDi0WUXgAUCcXGVwRuPADFGALjj1UeRqzhyAlHAC8APjgwoOADRKVa-AGl0eXQG0qrvB54VAC6TipwjBAwwCR4APKMAMIAFkwA5ugACuRgqLpmljbIjAAm6CTAjOglToSmQA
Steps to reproduce
Set notifyOnChangeProps query option to a function that (could) return undefined.
Expected behavior
No type error should occur.
How often does this bug happen?
Every time
Screenshots or Videos
No response
Platform
N/A
Tanstack Query adapter
None
TanStack Query version
5.29.2
TypeScript version
5.4.5
Additional context
No response
The resolution should be to just update https://github.com/TanStack/query/blob/1d60d44ad851472d37aaa3eef22ada07e5245989/packages/query-core/src/types.ts#L147
to
| (() => Array<keyof InfiniteQueryObserverResult> | 'all' | undefined)
Happy to open a PR if my understanding described above is correct.
Yes you are right. It will already work at runtime because if undefined is returned from the function, we treat it the same as if the prop itself is undefined:
https://github.com/TanStack/query/blob/4d5cc6679c1212af8a9d611fa0f535144feb2a19/packages/query-core/src/queryObserver.ts#L625
Happy to accept a PR to adapt the types 👍
