/ / parent
class BaseChart {

constructor(data){
    this.chartData = data.chartData || []; //
    this.title = data.title || ""; //
    this.xTitle = data.xTitle || ""; //x
    this.yTitle = data.yTitle || ""; //y
    this.xUnit = data.xUnit || ""; //x
    this.yUnit = data.yUnit || ""; //y
    this.vUnit = data.vUnit || ""; //value
    this.chartType = data.chartType || 0;
    this.dataType = data.dataType || 0; //
} 

}

/ / subclass
class PieChart extends BaseChart {

constructor(data){
    super(data);
    this.legenddata = [];
    this.vdata = [];
}

}

how to break the attribute output undifined, of the parent class?