[Docs]: for useSearchParams, functional updates should be explained in more detail

[YakovL]

Describe what's incorrect/missing in the documentation

Looking at https://reactrouter.com/en/main/hooks/use-search-params, one may think that to update one param while keeping the others, one can do:

const [searchParams, setSearchParams] = useSearchParams()

//...
const setPageNumber = (pageNumber: number) => setSearchParams(params => ({ ...params, page: String(pageNumber) }))

to update just the page portion of the query. However, this doesn't work: it removes all the query params and sets just the the page portion. (not sure if this is a bug or an intended behavior)

To work around this, one has to do:

const setPageNumber = (pageNumber: number) => setSearchParams(params => {
  params.set('page', String(pageNumber))
  return params
})

I think this is not trivial, and hence should be documented (unless it's a bug, I'm using 6.22.3).

[kiliman]

URLSearchParams is not a regular object, so you can't spread it like you normally would.

Instead, you need to convert the existing params into an object via Object.fromEntries()

const [searchParams, setSearchParams] = useSearchParams()

//...
const setPageNumber = (pageNumber: number) => 
  setSearchParams(params => ({ ...Object.fromEntries(params), page: String(pageNumber) }))

https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams/URLSearchParams

[depoulo]

IMHO the bigger undocumented caveat is that any mutation of searchParams (the first array entry returned), e.g. searchParams.delete('page') has the side effect of actually changing the URL.

[YakovL]

Yeah, both are relevant: the Object.fromEntries trick would be helpful there, and then an explanation of how to properly delete a param would be also useful. Is

setSearchParams(params => {
  const queryParams = Object.fromEntries(params)
  delete queryParams['page']
  return queryParams
})

sufficient to avoid side-effects?