Object.defineProperty doesn't define properties on 'this'

// @ts-check

class C {
  constructor() {
    Object.defineProperty(this, "x", { value: "hello" });

    this.x.toLowerCase();
  }
}

Expected: No error. Actual: Property 'x' does not exist on type 'C'.

[DanielRosenwasser]

@tokland This is about JavaScript analysis, not TypeScript.

[akornatskyy]

You need to add definite assertion assignment to property ‘x: string’.

class C {
  x!: string;  // definite assertion
  constructor() {
    Object.defineProperty(this, 'x', {value: 'hello'});
    this.x.toLowerCase();
  }
}