Arkanoid Ball -- taken from https://github.com/AlphaGit/random-javascript/blob/20c746aaa822ab66bf23dd6f249c7f19ee1546cc/arkanoid-canvas/arkanoid.js

Ball.js

Ball.prototype = Object.create(DrawableCircle.prototype);
Ball.prototype.constructor = DrawableCircle;
function Ball(drawingContext, color, radius, stageHeight, stageWidth) {
	var self = this;
	self.centerBall = function() {
		self.centerX = (stageWidth - radius*2) / 2;
		self.centerY = (stageHeight - radius*2) / 2;
	}
	self.centerBall();	
	
	DrawableCircle.call(this, drawingContext, color, radius, self.centerX, self.centerY);
	
	var move = function(dX, dY) {
		self.centerX += dX;
		self.centerY += dY;
	};
	
	var hitsBottom = function() {
		return stageHeight - radius <= self.centerY;
	};
	
	var hitsTop = function() {
		return self.centerY <= radius;
	};
	
	var hitsLeft = function() {
		return self.centerX <= radius;
	};
	
	var hitsRight = function() {
		return stageWidth - radius <= self.centerX;
	};
	
	return {
		centerBall: self.centerBall,
		draw: self.draw,
		move: move,
		hitsBottom: hitsBottom,
		hitsTop: hitsTop,
		hitsLeft: hitsLeft,
		hitsRight: hitsRight
	};
}