Ball.js

function Ball(radius, color) {
  if (typeof radius === 'undefined') {
    radius = 40;
  }
  if (typeof color === 'undefined') {
    color = '#FF0000';
  }
  this.x = 0;
  this.y = 0;
  this.vx = 0;
  this.vy = 0;
  this.radius = radius;
  this.color = color;
  this.scaleX = 1;
  this.scaleY = 1;
  this.rotation = 0;
  this.lineWidth = 1;
}
Ball.prototype.draw = function (context) {
  context.save();
  context.translate(this.x, this.y);
  context.rotate(this.rotation);
  context.scale(this.scaleX, this.scaleY);
  context.lineWidth = this.lineWidth;
  context.fillStyle = this.color;
  context.beginPath();
  context.arc(0, 0, this.radius, 0, (Math.PI * 2), true);
  context.closePath();
  context.fill();
  if (this.lineWidth > 0) {
    context.stroke();
  }
  context.restore();
};