JSON.stringify does not accept non-readonly object

[kku39]

Version

2.0.0-beta

Code

interface Param {
  id: string;
  value: number;
}
export function foo(param: Param, readonlyParam: Readonly<Param>) {
  JSON.stringify(param); // error
  JSON.stringify(readonlyParam);
}

Actual Behavior

Compile error: ts(2769) [6, 18]

No overload matches this call.
  Overload 1 of 2, '(value: ReadonlyJSONValue, replacer?: ((this: ReadonlyJSONValue, key: string, value: ReadonlyJSONValue) => any) | undefined, space?: string | ... 1 more ... | undefined): string', gave the following error.
    Argument of type 'Param' is not assignable to parameter of type 'ReadonlyJSONValue'.
      Type 'Param' is not assignable to type '{ readonly [x: string]: ReadonlyJSONValue | undefined; }'.
        Index signature for type 'string' is missing in type 'Param'.
  Overload 2 of 2, '(value: ReadonlyJSONValue, replacer?: (string | number)[] | null | undefined, space?: string | number | undefined): string', gave the following error.
    Argument of type 'Param' is not assignable to parameter of type 'ReadonlyJSONValue'.

Expected Behavior

No error

[uhyo]

Thank you for your feedback!

Given this issue and other problems related to JSON.stringify, I decided to switch to unknown and remove ReadonlyJSONValue.