[TypeScript] Non-null assertion operator, rxjs 설치 명령어

angular 강의를 듣던 중 그대로 따라쳤는데 오류가 났다. import { Component, OnInit } from '@angular/core'; import { ActivatedRoute } from '@angular/router'; import { Observable, ObservedValueOf } from 'rxjs'; import 'rxjs/add/operator/map'; @Component({ selector: 'app-developer', templateUrl: './developer.component.html', styleUrls: ['./developer.component.scss'] }) export class DeveloperComponent implements OnInit ..