Loading JSON data gives undefined object in Angular 2 - asynchronous? -

...component.ts:

import { component } '@angular/core'; import { valgteskolerservice } '../valgteskoler.service'; import { datoservice } './datoer.service';  @component({     selector: 'kalender',     providers: [datoservice],     templateurl: 'app/kalendervisning/html/kalender.html' }) export class kalendercomponent {      private valgteskoleruter: array<any> = [];     public datoer: any[] = [];      constructor(private valgteskolerservice: valgteskolerservice, private datoservice: datoservice) {         this.datoservice         .getdato()         .subscribe(datoer => { this.datoer = datoer; });     }      ngoninit() {       this.valgteskolerservice.hentlagretdata();       this.valgteskoleruter = this.valgteskolerservice.deltevalgteskoleruter;     }      antallruter: number = 0;     j: number = 0;      ukeen(mnd: number, aar: number) :cell[] {         var cells: array<cell> = [];         this.antallruter = 0;         (this.j = 1; this.j <= this.antalldager(mnd, aar); this.j++) {             var cell = new cell;             console.log(this.datoer[this.j].dato);             cell.id = this.datoer[this.j].dato;             cell.text = this.j;                    cells.push(cell);             this.antallruter++;             this.j = this.j;             if (this.antallruter % 7 == 0 && this.antallruter != 0) {                 break;             }         }         return cells;     }  class cell {     id: string;     text: number; } 

...service.ts:

import { injectable } '@angular/core'; import { http, response } '@angular/http'; import { observable } 'rxjs/observable';  @injectable() export class datoservice {       dato: array<any>;      constructor(private http: http) {}          getdato() {             return this.http.request('app/kalendervisning/datoer.json')                  .map(res => res.json());         }    } 

...json:

{         "dato": "2016-08-01"     }, etc. 

i struggling cell.id = this.datoer[this.j].dato statement in component. have checked browser inspector, , seems datoer array undefined until whole code has been run through several times. after while, array gets filled up. when tested console.log, prints 9 undefined objects, , actual data, reason repeated 2 times also. think there might problem data not loaded asynchronously, i'm not sure. there ideas why acts this, , have solution?

add constrctor code of calling api inside ngoninit :

ngoninit() {   this.datoservice     .getdato()     .subscribe(datoer => { this.datoer = datoer; });    this.valgteskolerservice.hentlagretdata();   this.valgteskoleruter =     this.valgteskolerservice.deltevalgteskoleruter; }