echarts：解决There is a chart instance already initialized on the dom问题

 if ( this.chartInstance != null && this.chartInstance != "" && this.chartInstance != undefined ) {
               this.chartInstance.dispose();
           }
       this.chartInstance = this.$echarts.init(this.$refs.chart, 'light');
       this.chartInstance.setOption(this.option);

先判断一下echarts实例是否存在，如果存在，就先dispose，然后再init成新的实例。