Ionic2 check if Component is already in Navigation Stack

variable.service.ts

  isAlready(name:string):number{
     if(name in this.viewcomponents)
     {
       let comp = this.viewcomponents[name];
       let views = this.nav.getViews();
       return views.map(function(x) {return x.component; }).indexOf(comp);

     }
    return -1;
  }