fix: JSON.parse accepts readonly arrays

closes #1

Author: uhyo

lib/lib.es5.d.ts

@@ -209,6 +209,16 @@ type JSONValue =
     }
   | JSONValue[];
 
+type ReadonlyJSONValue =
+  | null
+  | string
+  | number
+  | boolean
+  | {
+      readonly [K in string]?: ReadonlyJSONValue;
+    }
+  | readonly ReadonlyJSONValue[];
+
 interface JSON {
   /**
    * Converts a JavaScript Object Notation (JSON) string into an object.
@@ -227,8 +237,12 @@ interface JSON {
    * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
    */
   stringify(
-    value: JSONValue,
-    replacer?: (this: JSONValue, key: string, value: JSONValue) => any,
+    value: ReadonlyJSONValue,
+    replacer?: (
+      this: ReadonlyJSONValue,
+      key: string,
+      value: ReadonlyJSONValue
+    ) => any,
     space?: string | number
   ): string;
   /**
@@ -238,7 +252,7 @@ interface JSON {
    * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
    */
   stringify(
-    value: JSONValue,
+    value: ReadonlyJSONValue,
     replacer?: (number | string)[] | null,
     space?: string | number
   ): string;

tests/es5.ts

@@ -78,7 +78,17 @@ expectType<{ foo: number; bar: string; baz: boolean }>(
 })();
 
 // JSON
-expectType<JSONValue>(JSON.parse("{}"));
+{
+  expectType<JSONValue>(JSON.parse("{}"));
+  const arr = [1, 2, "foo"];
+  expectType<string>(JSON.stringify(arr));
+  const obj = { foo: { bar: 1 } };
+  expectType<string>(JSON.stringify(obj));
+  const readonlyArr = [1, 2, 3] as const;
+  expectType<string>(JSON.stringify(readonlyArr));
+  const readonlyObj = { foo: { bar: 1 } } as const;
+  expectType<string>(JSON.stringify(readonlyObj));
+}
 
 // ArrayConstructor
 {