如何通过自定义，来将该图改为平滑曲线（smooth=1）的折线图？echarts custom配置项内容和展示

如题

      var data1 = [
    [0, 23],
    [1, 33],
    [2, 53],
    [3, 23],
    [4, 23],
    [5, 23],
    [9, 64],
    [6, 64],
    [7, 3],
    [8, 25]
]


function renderItem(params, api) {
    var yValue = api.value(1);
    var start = api.coord([api.value(0), yValue]);
    var size = api.size([1, yValue]);
    var style = api.style();
    console.log(size)
    if (yValue > 40) {
        style.fill = 'red'
    } else if (yValue > 10) {
        style.fill = 'green'
    } else {
        style.fill = 'blue'
    }


    return {
        // 当type = 'polyline'时，shape的值应该是什么。。。
        type: 'rect',
        shape: {
            x: start[0],
            y: start[1],
            width: size[0],
            height: size[1]
        },
        style: style
    };
}

option = {
    title: {
        text: 'Profit',
        left: 'center'
    },
    tooltip: {},
    xAxis: {
        scale: true
    },
    yAxis: {},
    series: [{
        type: 'custom',
        renderItem: renderItem,
        label: {
            normal: {
                show: true,
                position: 'top'
            }
        },
        dimensions: ['from', 'to', 'profit'],
        encode: {
            x: [0],
            y: 1,
            tooltip: [0, 1],
            itemName: 1
        },
        data: data1
    }]
};