Make objects have private/protected members

TypeScript supports public (default), protected and private accessors on class members.

Bad:

class Circle {
  radius: number;

  constructor(radius: number) {
    this.radius = radius;
  }

  perimeter() {
    return 2 * Math.PI * this.radius;
  }

  surface() {
    return Math.PI * this.radius * this.radius;
  }
}

Good:

class Circle {
  constructor(private readonly radius: number) {}
  perimeter() {
    return 2 * Math.PI * this.radius;
  }

  surface() {
    return Math.PI * this.radius * this.radius;
  }
}