Ball as Class with reaction function

Code

var bg = new Path.Rectangle({
    size: view.bounds,
    fillColor: 'black'
})

var radiusOfBrush = 50

function Ball(point) {
  this.path = new Path.Circle({
    radius: 10,
    fillColor: 'blue',
    center: point,
    applyMatrix: false,
    parent: group
  })
}

Ball.prototype = {
	iterate: function() {
    this.path.position.x += 200
  },

  update: function(event) {
    var point = new Point(event.x, event.y)

    if (point.isClose(this.path.position, radiusOfBrush)){
      this.path.fillColor = 'red'
      this.path.tweenTo({
        fillColor: 'red'
      }, 200)
    } else{
      this.path.fillColor = 'blue'
    }
  }
}

var balls = []
var numBalls = 40
var group = new Group()

for (var x = 0; x < numBalls; x++){
  for (var y = 0; y < numBalls/2; y++){
    var point = new Point(x * 20, y * 20)
    var ball = new Ball(view.center + point)
    balls.push(ball)
  }
}

function onMouseMove(event){
  for (var i = 0; i < balls.length; i++){
    balls[i].update(event.point)
  }
}

group.position = view.center