openlayers3中polygon上添加icon

var vectorSource = new ol.source.Vector();

var polygon = new ol.geom.Polygon([[[120.97, 23.1],[115.97, 15.1],[118.97, 13.1],[120.97, 20.1]]]).transform('EPSG:4326', 'EPSG:3857');
vectorSource.addFeature(
new ol.Feature({
geometry: polygon,
name : '面',
index : '1'
})

/*

*style可以一个数组类型的ol.style.Style，如下所示

*/
var vectorLayer = new ol.layer.Vector({
source: vectorSource,
style: function(feature){
return [
new ol.style.Style({
image: new ol.style.Icon(
anchorXUnits: 'fraction',
anchorYUnits: 'pixels',
src: './images/4.png'
})),
geometry: function (feature) {
var coordinates = feature.getGeometry().getCoordinates()[0];
return feature.getGeometry().getInteriorPoint();
}
}),
new ol.style.Style({
text: new ol.style.Text({
text: feature.get('name'),
fill: new ol.style.Fill({
color: '#ff0000'
})
}),
fill: new ol.style.Fill({
color: '#ff0000'
}),
stroke: new ol.style.Stroke({
color: '#ff0000'
})
})
]
}
});