Echarts multiple data overlay

this.polar = {

title : {
    text: " ",
    x:"center"
},
xAxis: {
    type: "category",
    data: []
},
yAxis: {
    type: "value"
},
series: [
    {
        data: [],
        type: "bar",
        barWidth: "30%" // 
    }
]

}
this.$refs.barCharts.setOption (this.polar, true)

set setOption (this.polar, true), data will still be overlaid, and the data is not entered by push, why?

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Mar.13,2021
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