I need to create a class, but later add a method to the class, and that method needs access to properties of the class. I've tried binding this, but it is undefined when the method runs.

class TestClass {
  constructor(callback) {
    this.name = "Test";
    this.doSomething = callback.bind(this); // WHY DOESN'T THIS WORK?
  }
}

const TestInstance = new TestClass(
  () => {
    console.log(`${this.name} is doing something!`);
  },
);

TestInstance.doSomething(); // this is undefined

Am I doing it wrong or is this not possible?

I'm aware I could create a new class that extends the first, and call super in the constructor to access the parent's this, but for other reasons I'd prefer not to create child classes.