Explicitly Defining Method Overrides

class Rectangle extends Shape {
  // see above

  draw(ctx: CanvasRenderingContext2D) {
// ^
// This member must have an 'override' modifier because it
// overrides a member in the base class 'Shape'.(4114)
    ctx.fillStyle = this.fillStyle;
    ctx.lineWidth = this.lineWidth;
    let a = this.points[0];
    let b = this.points[1];
    ctx.strokeRect(a.x, a.y, b.x - a.x, b.y - a.y);
  }
}