Component onInit Method to capture HTTP response

import {Component, OnInit} from '@angular/core';
import {HttpClient} from './http.service';
import {user} from './user';
import {Response, Request} from '@angular/http';

@Component({selector: 'my-app', templateUrl: './app.component.html'})
export class AppComponent implements OnInit {
    constructor(private Http : HttpClient) {
        this.URL ='http://localhost:3000/api';
    }
    Users : user[];
    loaded : boolean;
    URL : string;
    ngOnInit() {
        this.Http.get(this.URL)
            .map((response : Response) => response.json())
            .subscribe((result) => {
                this.Users = result;
                this.loaded = true;
            });
    }
    filterValueChange($event:any) {
        this.loaded = false;
        this.URL = 'http://localhost:3000'+ this.constructUrl($event);
        this.Http.get(this.URL)
        .map((response : Response) => response.json())
        .subscribe((result) => {
            this.Users = result;
            this.loaded = true;

        });
    }
 }