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fix(types): JSONParsed infer unknown values #4405

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Merged
merged 1 commit into from
Sep 12, 2025
Merged

fix(types): JSONParsed infer unknown values #4405

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38 changes: 38 additions & 0 deletions src/client/client.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,16 @@ import { validator } from '../validator'
import { hc } from './client'
import type { ClientResponse, InferRequestType, InferResponseType } from './types'

class SafeBigInt {
unsafe = BigInt(42)

toJSON() {
return {
value: '42n',
}
}
}

describe('Basic - JSON', () => {
const app = new Hono()

Expand Down Expand Up @@ -51,6 +61,8 @@ describe('Basic - JSON', () => {
.get('/hello-not-found', (c) => c.notFound())
.get('/null', (c) => c.json(null))
.get('/empty', (c) => c.json({}))
.get('/bigint', (c) => c.json({ value: BigInt(42) }))
.get('/safe-bigint', (c) => c.json(new SafeBigInt()))

type AppType = typeof route

Expand Down Expand Up @@ -81,6 +93,12 @@ describe('Basic - JSON', () => {
http.get('http://localhost/empty', () => {
return HttpResponse.json({})
}),
http.get('http://localhost/bigint', () => {
return HttpResponse.json({ value: BigInt(42) })
}),
http.get('http://localhost/safe-bigint', () => {
return HttpResponse.json(new SafeBigInt())
}),
http.get('http://localhost/api/string', () => {
return HttpResponse.json('a-string')
}),
Expand Down Expand Up @@ -151,6 +169,26 @@ describe('Basic - JSON', () => {
expect(data).toStrictEqual({})
})

it('Should get a `{}` content', async () => {
const client = hc<AppType>('http://localhost')
const res = await client['safe-bigint'].$get()
const data = await res.json()
expectTypeOf(data).toMatchTypeOf<{ value: string }>()
expect(data).toStrictEqual({ value: '42n' })
})

it('Should get an error response', async () => {
const client = hc<AppType>('http://localhost')
const res = await client.bigint.$get()
const data = await res.json()
expectTypeOf(data).toMatchTypeOf<never>()
expect(res.status).toBe(500)
expect(data).toMatchObject({
message: 'Do not know how to serialize a BigInt',
name: 'TypeError',
})
})

it('Should have correct types - primitives', async () => {
const app = new Hono()
const route = app
Expand Down
13 changes: 2 additions & 11 deletions src/context.ts
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Expand Up @@ -194,21 +194,12 @@ interface JSONRespond {
* @template T - The type of the JSON value or simplified unknown type.
* @template U - The type of the status code.
*
* @returns {Response & TypedResponse<SimplifyDeepArray<T> extends JSONValue ? (JSONValue extends SimplifyDeepArray<T> ? never : JSONParsed<T>) : never, U, 'json'>} - The response after rendering the JSON object, typed with the provided object and status code types.
* @returns {Response & TypedResponse<JSONParsed<T>, U, 'json'>} - The response after rendering the JSON object, typed with the provided object and status code types.
*/
type JSONRespondReturn<
T extends JSONValue | SimplifyDeepArray<unknown> | InvalidJSONValue,
U extends ContentfulStatusCode
> = Response &
TypedResponse<
SimplifyDeepArray<T> extends JSONValue
? JSONValue extends SimplifyDeepArray<T>
? never
: JSONParsed<T>
: never,
U,
'json'
>
> = Response & TypedResponse<JSONParsed<T>, U, 'json'>
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Contributor Author

@BarryThePenguin BarryThePenguin Sep 11, 2025

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I think this change could be a seperate PR.

From what I understand JSONParsed already contains types that do the same thing as SimplifyDeepArray, specifically

...
  : T extends ReadonlyArray<unknown>
  ? { [K in keyof T]: JSONParsed<InvalidToNull<T[K]>> }
  : ...

compared with SimplifyDeepArray

type SimplifyDeepArray<T> = T extends any[]
  ? { [E in keyof T]: SimplifyDeepArray<T[E]> }
  : Simplify<T>

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@yusukebe yusukebe Sep 12, 2025

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Indeed. We can remove SimplifyDeepArray. For now, I'll merge this PR.


/**
* Interface representing a function that responds with HTML content.
Expand Down
74 changes: 68 additions & 6 deletions src/utils/types.test.ts
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
import type { Equal, Expect, JSONParsed } from './types'
import type { JSONParsed, JSONValue } from './types'

describe('JSONParsed', () => {
enum SampleEnum {
Expand Down Expand Up @@ -78,6 +78,11 @@ describe('JSONParsed', () => {
type Expected = never
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})
it('should convert bigint type to never', () => {
type Actual = JSONParsed<bigint>
type Expected = never
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})
})

describe('array', () => {
Expand Down Expand Up @@ -154,6 +159,20 @@ describe('JSONParsed', () => {
})
})

describe('unknown', () => {
it('should convert unknown type to unknown', () => {
type Actual = JSONParsed<unknown>
type Expected = JSONValue
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})

it('Should convert unknown value to JSONValue', () => {
type Actual = JSONParsed<{ value: unknown }>
type Expected = { value: JSONValue }
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})
})

describe('Set/Map', () => {
it('should convert Set to empty object', () => {
type Actual = JSONParsed<Set<number>>
Expand Down Expand Up @@ -199,19 +218,62 @@ describe('JSONParsed', () => {
datetime: string
}
type Actual = JSONParsed<Post>
// eslint-disable-next-line @typescript-eslint/no-unused-vars
type verify = Expect<Equal<Expected, Actual>>
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})

it('Should convert bigint to never', () => {
type Post = {
num: bigint
}
type Expected = never
type Actual = JSONParsed<Post>
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})

it('Should convert bigint when TError is provided', () => {
type Post = {
num: bigint
}
type Expected = {
num: never
num: JSONValue
}
type Actual = JSONParsed<Post, never>
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})

it('Should convert bigint[] to never', () => {
type Post = {
nums: bigint[]
}
type Expected = never
type Actual = JSONParsed<Post>
// eslint-disable-next-line @typescript-eslint/no-unused-vars
type verify = Expect<Equal<Expected, Actual>>
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})

it('Should convert bigint[] when TError is provided', () => {
type Post = {
num: bigint[]
}
type Expected = {
num: JSONValue[]
}
type Actual = JSONParsed<Post, never>
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})

it('Should parse bigint with a toJSON function', () => {
class SafeBigInt {
unsafe = BigInt('42')

toJSON() {
return {
unsafe: '42n',
}
}
}

type Actual = JSONParsed<SafeBigInt>
type Expected = { unsafe: string }
expectTypeOf<Actual>().toEqualTypeOf<Expected>()
})
})
42 changes: 32 additions & 10 deletions src/utils/types.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -41,27 +41,49 @@ type IsInvalid<T> = T extends InvalidJSONValue ? true : false
type OmitSymbolKeys<T> = { [K in keyof T as K extends symbol ? never : K]: T[K] }

export type JSONValue = JSONObject | JSONArray | JSONPrimitive
// Non-JSON values such as `Date` implement `.toJSON()`, so they can be transformed to a value assignable to `JSONObject`:
export type JSONParsed<T> = T extends { toJSON(): infer J }
/**
* Convert a type to a JSON-compatible type.
*
* Non-JSON values such as `Date` implement `.toJSON()`,
* so they can be transformed to a value assignable to `JSONObject`
*
* `JSON.stringify()` throws a `TypeError` when it encounters a `bigint` value,
* unless a custom `replacer` function or `.toJSON()` method is provided.
*
* This behaviour can be controlled by the `TError` generic type parameter,
* which defaults to `bigint | ReadonlyArray<bigint>`.
* You can set it to `never` to disable this check.
*/
export type JSONParsed<T, TError = bigint | ReadonlyArray<bigint>> = T extends TError
? never
: T extends {
toJSON(): infer J
}
? (() => J) extends () => JSONPrimitive
? J
: (() => J) extends () => { toJSON(): unknown }
? {}
: JSONParsed<J>
: JSONParsed<J, TError>
: T extends JSONPrimitive
? T
: T extends InvalidJSONValue
? never
: T extends ReadonlyArray<unknown>
? { [K in keyof T]: JSONParsed<InvalidToNull<T[K]>> }
: T extends Set<unknown> | Map<unknown, unknown>
? { [K in keyof T]: JSONParsed<InvalidToNull<T[K]>, TError> }
: T extends Set<unknown> | Map<unknown, unknown> | Record<string, never>
? {}
: T extends object
? {
[K in keyof OmitSymbolKeys<T> as IsInvalid<T[K]> extends true
? never
: K]: boolean extends IsInvalid<T[K]> ? JSONParsed<T[K]> | undefined : JSONParsed<T[K]>
}
? T[keyof T] extends TError
? never
: {
[K in keyof OmitSymbolKeys<T> as IsInvalid<T[K]> extends true
? never
: K]: boolean extends IsInvalid<T[K]>
? JSONParsed<T[K], TError> | undefined
: JSONParsed<T[K], TError>
}
: T extends unknown
? JSONValue
: never

/**
Expand Down
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