错误TypeError：a.addEventListener不是一个函数，openlayers 3

Question

我正在尝试缓冲openlayers 3中的矢量要素，但是我收到以下错误：

ERROR TypeError: a.addEventListener is not a function

这是我的代码：

var radius = 5,
        format = new ol.format.WKT()
    var reader = new jsts.io.WKTReader()
    var geom = reader.read(format.writeGeometry(this.Feature.getGeometry()))
    var buffered = geom.buffer(radius)

    var writer = new jsts.io.GeoJSONWriter()
    buffered = writer.write(buffered)
var nfeature = {
    type: 'Feature',
    geometry: buffered,
    properties: {}
}
this.VectorOverlay.getSource().addFeature(nfeature) <= error