tmp: string;

constructor(private http: Http) {
  this.tmp = "load";
  this.GetUsers();
}

ngOnInit() {
  setTimeout(console.log("Hello"), 2000);
}
GetUsers() {
   this.http.get('http://localhost:1337/api/users')
    .toPromise()
     .then(function(response) {
       this.tmp = "success"
     })
    .catch(this.handleError);

public tmp: string;

constructor(private http: HttpClient) { // не забудь заимпортить этот модуль

}

ngOnInit() {
  setTimeout(console.log("Hello"), 2000);
  this.GetUsers()
     .do(() => this.tmp = 'load')
     .subscribe(data => {
        this.tmp = data;
      });
}

private getUsers(): Observable<any> {
  return this.http.get<any>('http://localhost:1337/api/users')
}