[jackdempsey2015]

Data=function(name, coObject){
  this.name=name
  this.coObject=coObject
}

Object.defineProperty(Data.prototype, "y", {get: function(){return -this.coObject[0]}})

series1=[{
            color : "foo",
            name : 'Negative Difference',
            data : [15, 0, 0, 0, 0, 0, 0, 0],
            stack : '1'
        }]

series2=[{
            upColor: "foo",
            color: "foo",
            data: [new Data("0", series1[0].data)]
        }]

alert(series2[0].data[0].y)

series1[0].data[0]=20

alert(series2[0].data[0].y)


//>>>> -15
//>>>> -20