Cannot use `override` keyword to override methods of `Object` without explicitly extending `Object`

Bug Report

🔎 Search Terms

override, TS4112

🕗 Version & Regression Information

It happens in 4.4.2 and has been there since the introduction of override keyword (#39669).

⏯ Playground Link

https://www.typescriptlang.org/play?#code/MYGwhgzhAECC0G8BQ1oHsBuBTATjglgCZbQAuaAyqQQHYDmAFAJSKo5akCuON0A5ADM0aPgG5oAXyQSgA

💻 Code

class A {
  override toString() { return 'foo'; }
}

🙁 Actual behavior

TS4112: This member cannot have an 'override' modifier because its containing class 'A' does not extend another class.

🙂 Expected behavior

It should be allowed, since the method overrides Object.prototype.toString.

Per ECMAScript spec §15.7.12.7, a class without an explicit extends clause would be implicitly inheriting from Object. Therefore, such classes should be allowed to explicitly override methods declared in Object.

リンクされた TypeScript Playground でこのケースを再現し、lib/lib.es5.d.ts の Object の宣言を調べてください。明示的な extends 句を持たないクラスに対する override チェックの動作を追跡してください。他のケースでは override チェックが引き続き適用される一方で、例が受け入れられれば完了です。