Prevent memory leaves with Observables

display-cuisine.component.ts

private subscription;
cuisines;

constructor(private _af: AngularFire) {}

ngOnit() {
  this.subscription = this._af
    .database.list('cuisines')
    .subscribe( () => {
      this.cuisines = x;
      console.log(this.cuisines);
    });
}

ngOnDestroy() {
  this.subscription.unsubscribe();
}