百度地图拖动会卡是怎么回事

```c++
cityData.forEach((item,ix)=>{
                                //PolyData.push(new BMap.Point(item.longitude, item.latitude))
                                // map.addOverlay(new BMap.Marker(
                                //   new BMap.Point(item.longitude, item.latitude)
                                // ), {
                                //     strokeColor: 'blue',
                                //     strokeWeight: 2,
                                // });
                                if(ix>=0){
                                    let data=item.split(" ");
                                    let i=0
                                    let PolyData=[]
                                    for(let is=0;i<data.length;is++){
                                        PolyData.push(new BMap.Point(data[i],data[i+1]))
                                        i=i+2;
                                    }
                                    var polyline = new BMap.Polygon(PolyData, {
                                            strokeColor: colors,
                                            strokeWeight: 5,
                                            strokeOpacity: 1
                                    });
                                    map.addOverlay(polyline);
                                    PolyData = []
                                }
                                
                            })

```