Angular 5 ActivatedRoute和FlatMap

Question

我正在尝试根据没有嵌套.subscribes的查询参数发出http请求。

this.activeRoute.queryParamMap
.map((params: ParamMap) => params.get('query'))
.flatMap(query => this.httpService.getWeatherForecast(query))
.subscribe( .......)

但是，我收到以下错误

this.activeRoute.queryParamMap.map is not a function