RPC infers "never" if type is "any | undefined"

[tartuke]

What version of Hono are you using?

4.6.2

What runtime/platform is your app running on? (with version if possible)

bun

What steps can reproduce the bug?

import { Hono } from "hono";
import { hc } from "hono/client";

export const route = new Hono().get("/even", async (c) => {
  const num = Math.floor(Math.random() * 100);

  const res = num % 2 === 0 ? num : undefined;

  return c.json(res); // return a "number" if even, "undefined" if odd
});

const api = hc<typeof route>("/");

const budget = await (await api.even.$get()).json();

console.log(typeof budget); // should be "number | undefined", but is "never"

What is the expected behavior?

No response

What do you see instead?

No response

Additional information

No response

[EdamAme-x]

This is because JSON does not accept undefined as a value.

https://github.com/honojs/hono/blob/main/src/utils/types.ts#L27

The following will cure the problem, but it is not in accordance with the specification.

- export type JSONPrimitive = string | boolean | number | null
+ export type JSONPrimitive = string | boolean | number | undefined | null

[EdamAme-x]

undefined is empty when stringified.
Empty strings cannot be parsed. Therefore, it is in accordance with the specification that the types is never.
Converting undefined to null solves the problem.

I do not think this is a bug.

[yusukebe]

Hi @tartuke

This is not a bug. Because, as @EdamAme-x said, parsing an empty string in the client will result in an error, so in that case, the expected type is never.

const res = await route.request('/even')
await res.json() // Error!

[yusukebe]

@askorupskyy

I think number is a valid JSON value, right?

[askorupskyy]

nvm @yusukebe i made a mistake. was having the same issue and my train of thought went in a wrong direction. either way, i think tightening the types should solve this

[github-actions]

This issue has been marked as stale due to inactivity.

[github-actions]

Closing this issue due to inactivity.