title: How to execute subscribe into another subscribe in Angular 4?
body: <p>I guess my problem has a pretty simple solution but I did not find one.
  I want to write the value of the second subscribe</p>
  
  <pre><code> export class ArticleDetailComponent implements OnInit  {
  
    private  articleID: any;
    public   detailArticle: any ;
  
  
    constructor( private route: ActivatedRoute , private _articlesService: ArticlesService ) {
    }
  
    ngOnInit () {
       this.route.params.subscribe( (params) =&gt; {
        this.articleID = params['id'];
         this._articlesService.getArticle(this.articleID).subscribe( article =&gt; this.detailArticle = article );
       }
      );
    }
  }
  </code></pre>
  
  <p>I want to write the value of the second subscribe into "<code>detailArticle</code>"
  But because I already call one Subscribe , i think there is a difference in the requests and the time they arrive.
  And in the value it records a "undefined" 
  How can I sync the two Subscribes()  when one of them is into another ?
  The idea is to set the resulting value of <code>detailArticle</code> So I can use it in the template . </p>