<select class="chooseWatchlist" (change)="updateWatchlistTable(item.name)">
   <option *ngFor="let item of _items">{{ item.name }}</option>
</select>

private updateWatchlistTable(name) {
  this.http.get('http://localhost:8080/api/points/getValue/' + name)
   .subscribe(res => this._watchlistElements = res.json());
  console.log(name);
}