如何在Angular 4中导航到新页面时获取上一页URL

Question

我尝试给出以下代码。但是以前的网址无法进入服务页面

previousUrl: string;
constructor(router: Router) {
  router.events
  .filter(event => event instanceof NavigationEnd)
  .subscribe(e => {
    console.log('prev:', this.previousUrl);
    this.previousUrl = e.url;
  });
}