class Entity {
    constructor(x, y, boundingRect) {
            this.x = x;
        this.y = y;
        this.boundingRect = boundingRect;
    }
}

class Enemy extends Entity {
        constructor() {
            let boundingRect = { x: this.x, y: this.y + 10, w: 20,  h: 20 };
        super(42, 42, boundingRect);
    }
}