I have this component:

export class CategoryDetailComponent implements OnInit{ category: Category; categoryProducts: Product[]; errorMessage: string; constructor(private _categoryService: CategoryService, private _productService: ProductService, private _routeParams: RouteParams ) {} ngOnInit() { this.getCategoryAndProducts(); } getCategoryAndProducts() { let categoryName = this._routeParams.get('name'); let categoryId = this.routeParams.get('id'); var params = new URLSearchParams(); params.set('category', categoryName); Observable.forkJoin( this._categoryService.getCategory(categoryId), this._productService.searchProducts(params) ).subscribe( data => { //this displays the expected category's name. console.log("category's name: "+ data[0].attributes.name) this.category = data[0]; this.categoryProducts = data[1]; }, error => this.errorMessage = <any>error ) } }

In the component's template I have this:

<h1>{{category.attributes.name}}</h1>

When I navigate to this component, I get an error:

TypeError: cannot read property 'attributes' of undefined

why is the category property on the template undefined and how can I solve this?

The bindings in the template are evaluated before ngOnInit() . To prevent Angular to throw an error you can use

<h1>{{category?.attributes.name}}</h1>

The Elvis operator prevents Angular evaluating .attributes... unless category has a value.

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