new.target is not inferred as a "this" type

[justinfagnani]

TypeScript Version: [email protected]

Code

class A {
  a: this;

  constructor() {
    super();
    this.a = Object.create(new.target.prototype); // [ts] Type 'A' is not assignable to type 'this'.
    this.a = new (new.target)(); // [ts] Type 'A' is not assignable to type 'this'.
  }
}

The assignment should be allowed in both cases.

Expected behavior:

No errors

Actual behavior:

Errors

[rbuckton]

We don't currently expose a this type for the static side of a class, and we do not currently expose the prototype of the static side of a class as a this type. Until such time as we decide to change that behavior, this is functioning as intended.

Please note that you can avoid the error by introducing a type assertion in both cases:

class A {
  a: this;

  constructor() {
    this.a = Object.create(<this>new.target.prototype);
    this.a = <this>new (new.target)();
  }
}