Atomy Game for two Players with refactored code

Hi, nothing new on the outside. But on the inside we added a new data structure for coordinates:

/* Constructor */
var XY = function (x, y){
    this.x = x || 0;
    this.y = y || 0;
}

Some of its functions:

XY.prototype.add = function(xy){
    return new XY(this.x + xy.x, this.y + xy.y);
}
XY.prototype.equals = function(xy){
    return (this.x == xy.x, this.y  == xy.y);
}