gistfile1.txt

updateSize: function(width, height){

    // get current center
    var centerX = this.pos.x + this.size.x/2,
        centerY = this.pos.y + this.size.y/2;

    // set new width / height
    this.size.x = width;
    this.size.y = height;
    
    // make the center coord match what it was previously
    this.pos.x = centerX - this.size.x/2;
    this.pos.y = centerY - this.size.y/2;
}