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Fix/Refine Type Inference for Objects with toJSON() Extending Primitives #690

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merged 2 commits into from
Oct 17, 2023
Merged

Fix/Refine Type Inference for Objects with toJSON() Extending Primitives #690

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445eb76
Refine Type Inference for Objects with toJSON() Extending Primitives
nrako Sep 23, 2023
a96e9cf
Merge branch 'main' into fix_nonjson_extending_primitive
sindresorhus Oct 17, 2023
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36 changes: 18 additions & 18 deletions source/jsonify.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -96,24 +96,24 @@ export type Jsonify<T> = IsAny<T> extends true
? null
: T extends JsonPrimitive
? T
: // Instanced primitives are objects
T extends Number
? number
: T extends String
? string
: T extends Boolean
? boolean
: T extends Map<any, any> | Set<any>
? EmptyObject
: T extends TypedArray
? Record<string, number>
: T extends NotJsonable
? never // Non-JSONable type union was found not empty
: // Any object with toJSON is special case
T extends {toJSON(): infer J}
? (() => J) extends () => JsonValue // Is J assignable to JsonValue?
? J // Then T is Jsonable and its Jsonable value is J
: Jsonify<J> // Maybe if we look a level deeper we'll find a JsonValue
: // Any object with toJSON is special case
T extends {toJSON(): infer J}
? (() => J) extends () => JsonValue // Is J assignable to JsonValue?
? J // Then T is Jsonable and its Jsonable value is J
: Jsonify<J> // Maybe if we look a level deeper we'll find a JsonValue
: // Instanced primitives are objects
T extends Number
? number
: T extends String
? string
: T extends Boolean
? boolean
: T extends Map<any, any> | Set<any>
? EmptyObject
: T extends TypedArray
? Record<string, number>
: T extends NotJsonable
? never // Non-JSONable type union was found not empty
: T extends []
? []
: T extends unknown[]
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15 changes: 15 additions & 0 deletions test-d/jsonify.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,21 @@ expectNotAssignable<JsonValue>(nonJsonWithToJSON);
expectAssignable<JsonValue>(nonJsonWithToJSON.toJSON());
expectAssignable<Jsonify<NonJsonWithToJSON>>(nonJsonWithToJSON.toJSON());

class NonJsonExtendPrimitiveWithToJSON extends Number {
public fixture = BigInt('42');

public toJSON(): {fixture: string} {
return {
fixture: '42n',
};
}
}

const nonJsonExtendPrimitiveWithToJSON = new NonJsonExtendPrimitiveWithToJSON();
expectNotAssignable<JsonValue>(nonJsonExtendPrimitiveWithToJSON);
expectAssignable<JsonValue>(nonJsonExtendPrimitiveWithToJSON.toJSON());
expectAssignable<Jsonify<NonJsonExtendPrimitiveWithToJSON>>(nonJsonExtendPrimitiveWithToJSON.toJSON());

class NonJsonWithToJSONWrapper {
public inner: NonJsonWithToJSON = nonJsonWithToJSON;
public override = 42;
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