Angular8和OpenLayers 6:错误TypeError:无法读取未定义的属性“”forEachFeatureAtPixel“”

import { Component, OnInit } from '@angular/core';
import Map from 'ol/Map';
import View from 'ol/View';
import TileLayer from 'ol/layer/Tile';
import OSM from 'ol/source/OSM';
import { fromEvent } from 'rxjs';

@Component({
  selector: 'app-map',
  templateUrl: './map.component.html',
  styleUrls: ['./map.component.css']
})
export class MapComponent implements OnInit {
  map: Map;

  ngOnInit() {
    this.initMap();
  }

  initMap() {
    const map = new Map({
      target: 'map',
      layers: [
        new TileLayer({
          source: new OSM()
        })
      ],
      view: new View({
        center: [0, 0],
        zoom: 2
      })
    });

    this.map = map;

    // 添加点击事件监听器
    fromEvent(this.map.getViewport(), 'click').subscribe(event => {
      const pixel = this.map.getEventPixel(event);
      this.map.forEachFeatureAtPixel(pixel, (feature) => {
        // 处理要素对象
        console.log(feature.getProperties());
      });
    });
  }
}