Support undefined as a default value in Parsers

[taylorjohnwood]

For better or worse, some applications have a strict semantic difference between null and undefined. Would it be possible to support undefined as a default for parsers?

e.g

parseAsInteger.withDefault(undefined) // Allow this, currently due to typing it does not work.

I'm happy to raise a PR for this if people agree it belongs in Nuqs!

[franky47]

You could wrap your useQueryState hook to get this behaviour:

function useUndefinedQueryState() {
  const [state, setState] = useQueryState('my-key')
  return [state ?? undefined, setState] as const
}

You would still have to set the value to null to remove it from the URL though, which might cause confusion as you'd get undefined back.

If you want to try your hand at a PR, the hardest part will be updating the type definitions, and the clearOnDefault option runtime code might require some tweaking to properly handle undefined.

[taylorjohnwood]

Yes good suggestion :) I've currently wrapped a lot of my parsing to get this behavior, but as you mentioned removing query params requires null. My other complications with wrapping are:

1. We reuse the same parsers across multiple pages and there is a chance that someone one accidentally forgets to wrap them.
2. I'm usually parsing objects so the wrapping is a little more tedious

const [coordinates, setCoordinates] = useQueryStates(
  {
    lat: parseAsFloat.withDefault(45.18),
    lng: parseAsFloat.withDefault(5.72),
    ... // many more params
  },
)

const coordinatesWithUndefined = {
  lat: lat ?? undefined,
  lng: lng ?? undefined,
  ... // repeat for all query params
} 

I'm going to raise a PR soon I think. Thanks for your quick reply

[franky47]

Sounds good, please review the contribution guidelines to get started. Adding typing tests (*.test-d.ts) will be key here to make sure type updates behave correctly.