echarts的折线图动态分层

var xData = param.xData;

    var data = param.yData    let option = [];    let num =param.num ? param.num : 0;    let max = num ? num *100 : 100;    //处理精度丢失问题  但不是最佳方案    let startValue = param.startValue;    visualMap: [{            show: false,            top: 20,            right: 10,            default:10,            pieces:[{   //分层的实现主要是在里代码                gt: 0,                lte: num,                color: '#ffde33'            },{                gt: num,                lte: max,                color: '#f00'            }],            outOfRange: {           // 超出范围                color: '#f00'            }        }],        title: [{            top: '',            left: 'center',            text: param.title,        }],        tooltip: {            trigger: 'axis',            formatter: function(params){                    var text_Unit ='';                     for(var i = 0;i < params.length;i++){                    text_Unit += params[i].value + param.Unit + "</br>"                }                        return params[0].name + "</br>" + text_Unit;                                  }        },        xAxis: [{            data: xData,            gridIndex: 1,        }],        yAxis: [{            name: param.yName,            splitLine: { show: false },            gridIndex: 1,        }],        grid: [{            bottom: '',        }, {            top: '20%',        }],        series: {            type: 'line',            showSymbol: false,            data: data,            markLine: {                silent: true,                data: [{                    yAxis: num                },]            }        }