最近再做缓冲区的绘制，然后在网上各种查资料，最后决定用turf来实现; 刚开始这样写的，然后不出现缓冲区

      var line = turf.lineString([[8940117.74537665,5936319.233970245],[10407708.688452033,5740640.441560194],[10466412.326175049,5359066.796360594]]);
      var buffered = turf.buffer(line , val, {units: 'kilometers'});
      //创建数据geojson对象和数据源对象
      var format = new GeoJSON();
      var source = new VectorSource({ wrapX: false });
      // //读取geojson数据
      var lineFeature  = format.readFeature(line);
      var bufferFeature = format.readFeature(buffered);
      // //将数据添加数据源的
      source.addFeature(lineFeature);
      source.addFeature(bufferFeature);
      var test = new VectorLayer({ source: source })
      this.map.addLayer(test)

并且还如下得错误 然后开始在网上查资料后，知道turf缓冲区不能用EPSG:3857的坐标系，需要转成EPSG:4326(关于坐标系不清楚得,可以看这里) 然后我转过后再试验

      let coordinates = '[[8940117.74537665,5936319.233970245],[10407708.688452033,5740640.441560194],[10466412.326175049,5359066.796360594]]';
      let bufferCoordinates = [],pointTransform=[];
      for (var i = 0; i < coordinates.length; i++) {
          pointTransform = transform(coordinates[i], "EPSG:3857", "EPSG:4326");
          bufferCoordinates.push(pointTransform);
        }
        var line = turf.lineString(bufferCoordinates);
        var buffered = turf.buffer(line , val, {units: 'kilometers'});
      //创建数据geojson对象和数据源对象
      var format = new GeoJSON();
      var source = new VectorSource({ wrapX: false });
      // //读取geojson数据
      var lineFeature = format.readFeature(line);
      var bufferFeature = format.readFeature(buffered);
      // //将数据添加数据源的
      source.addFeature(lineFeature);
      source.addFeature(bufferFeature);
      var test = new VectorLayer({ source: source })
      this.map.addLayer(test)

到了这里发现虽然不报错了，但是结果还是不出来，然后这样看来代码没问题，我这个时候就开始写demo，然后在demo中查看发现运行是没问题得； 那就奇了怪了,到底是哪里还有问题，最后又看了一遍官方文档，然后加上了以下两行代码

lineFeature.getGeometry().transform('EPSG:4326', 'EPSG:3857');
bufferFeature.getGeometry().transform('EPSG:4326', 'EPSG:3857');

再次运行，成功出现缓冲区：

 

 参考：openlayers+turf.js实现缓冲区得绘制