🔎 Search Terms

class extends null interface

🕗 Version & Regression Information

• This is the behavior in every version I tried (at least up until 3.3, which is the oldest build in the playground).

⏯ Playground Link

https://www.typescriptlang.org/play?lib=true&ts=5.1.6#code/JYOwLgpgTgZghgYwgAgEJwM4oN4CgC+uuCANphsgMLIQAekIAJhSAK4knJ7I-IID2IDGCisEYflAAUASi65eyQoVCRYiFNToNmaTDnxA

💻 Code

interface Base {
}

class C extends null {
    constructor() {
    }
}
interface C extends Base {}

🙁 Actual behavior

Reports the following error:

Class static side 'typeof C' incorrectly extends base class static side 'null'.

🙂 Expected behavior

No error. inteface Base does not describe the static side of anything, and reopening a class using something like interface C extends Base {} is common practice for shims.

Additional information about the issue

I ran into this when implementing a class that utilizes return override in a constructor when combined with class extends null while experimenting with the Shared Structs origin trial (whose constructors produce objects with a null prototype). Though native extends null has some issues in ES2015+, it still works fine with explicit return override in a constructor in any engine:

class C extends null {
  constructor() {
    return {};
  }
}
new C(); // works just fine.