openlayers4 lineString无法绘制折线，为直线

如果你也遇到了这个问题，试着把坐标转成number类型，还是要按照文档来啊

let center = item.center;
    if (this.mapModel.track.getGeometry()) {
        this.mapModel.track.getGeometry().appendCoordinate(center);
    } else {
        let polyline = new Polyline();
        this.mapModel.track.setGeometry(new LineString([center])); 
    }

function addTrack(item){
    console.log(item.center)
    let center = item.center.map(parseFloat);
    if (this.mapModel.track.getGeometry()) {
        this.mapModel.track.getGeometry().appendCoordinate(center);
    } else {
        let polyline = new Polyline();
        this.mapModel.track.setGeometry(new LineString([center])); 
    }
}