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

     boundingBox() {
       return {
         left: this.x,
         right: this.x + this.width,
         top: this.y,
         bottom: this.y + this.height
       };
     }

     draw(ctx) {
       ctx.fillStyle = "white";
       ctx.fillRect(this.x, this.y, this.width, this.height);
     }
   }
