TS2409 is an invalid error.

TypeScript Version: 3.3.0-dev.20181222

Search Terms: TS2409

Code

class A {
  constructor() {
    // return an arrow function
    return message => {
      this._message = message;

      return this;
    };
  }

  bar() {
    console.log(this._message);
  }
}

const a = new A();
a('hello world').bar(); // 'hello world'

Expected behavior:
No error.

Actual behavior:
src/test.ts(4,5): error TS2409: Return type of constructor signature must be assignable to the instance type of the class.

I should be able to override the object returned from a constructor.

Normally constructors don't return a value, but they can choose to do so if they want to override the normal object creation process.

Souce: MDN - new operator

Start with the TypeScript code sample and investigate how constructor return types are checked against the class instance type. Compare the reported TS2409 behavior with JavaScript's constructor-return semantics; done means the intended valid case is accepted without weakening unrelated constructor checking.