（Vue中）cehart在同一个dom上画图，切换时饼图有折线图的坐标系

网上都是别人转载的，下面是转载的代码，在Vue中根本不适用

var echartrunningstate = null;

if (echartrunningstate && echartrunningstate.dispose) {
echartrunningstate.dispose();
}
echartrunningstate = echarts.init(document.getElementById("main"));

echartrunningstate一直是undefined，需要将echartrunningstate放在外层才能找到