How to identify when an infinite query is for "previous pages" or "next pages"?

[jpenna]

Currently, when using useInfiniteQuery, the pageParam only gives the cursor value, but nothing about the direction it should be used.

I'd like to do something like the following:

useInfiniteQuery({
    queryKey: 'key,
    initialPageParam: undefined as number | undefined,
    staleTime: Infinity,
    queryFn: async ({ pageParam }) => {
     const response = await getTopicMessages({
        path: { topicId },
        query: isNext ? { last: pageParam } : { first: pageParam }, // if there was a `isNext` param
      });

      return {
        data: response.data.info,
        next: response.data.next,
        previous: response.data.previous,
      };
    },
    getNextPageParam: (lastPage) => {
      return lastPage.next;
    },
    getPreviousPageParam: (firstPage) => {
      return lastPage.previous;
    },
  });

In the backend, if last is given, I do > cursor (next), otherwise I do < cursor (previous).

The work around I found was returning an array with the isNext value:

useInfiniteQuery({
    queryKey: 'key,
    initialPageParam: undefined as number | undefined,
    staleTime: Infinity,
    queryFn: async ({ pageParam }) => {
      const [isNext, cursor] = pageParam
      
       const response = await getTopicMessages({
        path: { topicId },
        query: isNext ? { last: cursor } : { first: cursor }, // if there was a `isNext` param
      });

      return {
        data: response.data.info,
        next: response.data.next,
        previous: response.data.previous,
      };
    },
    getNextPageParam: (lastPage) => {
      return lastPage.next ? [true, lastPage.next] : undefined;
    },
    getPreviousPageParam: (firstPage) => {
      return lastPage.previous ? [true, lastPage.previous] : undefined;
    },
  });

[TkDodo]

we do pass the direction into the queryFn:

queryFn: ({ pageParam, direction }) => ...

direction is: 'forward' | 'backward'