custom为何不显示echarts line' }, { type: 'custom配置项内容和展示

      option = {
    xAxis: {
        type: 'category',
        data: ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
    },
    yAxis: {
        type: 'value'
    },
    series: [
        {
            data: [820, 932, 901, 934, 1290, 1330, 1320],
            type: 'line'
        }, 
        {
           type: 'custom',
           renderItem: renderItem,
           /*xAxisIndex: 1,*/
            data: [[200, 20, 300, 40], [120, 150, 50, 60], [70, 80, 90, 100]]
        }
    ]
};

function renderItem(params, api) {
    var points = [[api.value(0), api.value(1)],[api.value(2), api.value(3)]];
    console.log(points);
    return {
        
        type: 'polygon',
       // type: 'line',
        // shape: {
        //      x1: api.value(0),
        //      y1: api.value(1),
        //      x2: api.value(2),
        //      y2: api.value(3),
        // },
        shape: {
            points: echarts.graphic.clipPointsByRect(
                points,
                    {
                        x: params.coordSys.x,
                        y: params.coordSys.y,
                        width: params.coordSys.width,
                        height: params.coordSys.height
                    }
            )
        },
        /*style: api.style()*/
        style: {
            stroke: 'black',
            fill: 'black'
        }
    }
    
}