Why pageParams is undefined on init?

[behzadam]

I'm not sure this is a bug report or not but the question is why pageParams initial item is undefined? I expect it to be 1 and not undefined. I'm preparing a simple example of using React Query and Graphql and the demo is here.
Also, you can check the issue in CharacterList component:
useEffect(() => { console.log(data?.pageParams) }, [data])

[TkDodo]

pageParam is derived from the previous page via getNextPageParam. Since the first page has no previous page, what else should it be?

That is why we assign a default value in the example:

useInfiniteQuery(
    'projects',
    async ({ pageParam = 0 }) => {
      const res = await axios.get('/api/projects?cursor=' + pageParam)
      return res.data
    },
    {
      getNextPageParam: lastPage => lastPage.nextId ?? undefined,
    }
  )

in that case, undefined gets coerced to 0

[behzadam]

Thank you @TkDodo. Recently, I read the document in two days and tried to make a demo and your answers were helpful for me.

[amirfrd]

@TkDodo
so in nextjs when try to prefetchInfiniteQuery because of that undefined can't return from getServerSideProps

Error: Error serializing .dehydratedState.queries[0].state.data.pageParams[0]returned fromgetServerSidePropsin "/store/[id]". Reason:undefinedcannot be serialized as JSON. Please usenull or omit this value.

[TkDodo]

it's fixed in v5

[sbbu]

can you fix it in v4

[TkDodo]

no