ES6:类型“object”上不存在属性“selected”

从“amcharts4 codepen pre-selecting areas”中,我想将JS转换为ES6。但是,我出错了

错误TS2339:类型“object”上不存在属性“selected”。

我要转换的代码如下:

// Create map instance
let chart = am4core.create("chartdivmap", am4maps.MapChart);

// Set map definition
chart.geodata = am4geodata_worldHigh;

// Set projection
chart.projection = new am4maps.projections.Miller();

// Center on the groups by default
chart.homeZoomLevel = 1.5;
chart.homeGeoPoint = {
    longitude: 10,
    latitude: 52
};

// Polygon series
let polygonSeries = chart.series.push(new am4maps.MapPolygonSeries());
polygonSeries.useGeodata = true;


var polygonTemplate = polygonSeries.mapPolygons.template;
polygonTemplate.tooltipText = "{name}";
polygonTemplate.fill = chart.colors.getIndex(0);

// Hover state
var hs = polygonTemplate.states.create("hover");
polygonTemplate.fill = am4core.color("#CCCCCC");
hs.properties.fill = am4core.color("#010101");

polygonTemplate.adapter.add("fill", function(fill, target) {
    if (target.dataItem.dataContext && target.dataItem.dataContext.selected) {
        return am4core.color("#666666");
    }
    return fill;
});

我尝试过 let k:any = target; 像这样传递变量 function(fill, target, k) 并试图捕捉到这样的价值: k.dataItem.dataContext.selected 这给了我更多的错误。