How do I filter an array with TypeScript in Angular 2?
<p>ng-2 parent-child data inheritance has been a difficulty for me. </p>

<p>What seems that could be a fine working practical solution is filtering my total array of data to an array consisting of only child data referenced by a single parent id.
In other words: data-inheritance becomes data filtering by one parent id. </p>

<p>In a concrete example this can look like: filtering a books array to only show the books with a certain <code>store_id</code>.</p>

<pre class="lang-ts prettyprint-override"><code>import {Component, Input} from 'angular2/core';

export class Store {
  id: number;
  name: string;
}

export class Book {
  id: number;
  shop_id: number;
  title: string;
}

@Component({
  selector: 'book',
  template:`
    &lt;p&gt;These books should have a label of the shop: {{shop.id}}:&lt;/p&gt;

    &lt;p *ngFor="#book of booksByShopID"&gt;{{book.title}}&lt;/p&gt;
  `
])
export class BookComponent {
  @Input()
  store: Store;

  public books = BOOKS;

  // "Error: books is not defined"
  // ( also doesn't work when books.filter is called like: this.books.filter
  // "Error: Cannot read property 'filter' of undefined" )
  var booksByStoreID = books.filter(book =&gt; book.store_id === this.store.id)
}

var BOOKS: Book[] = [
  { 'id': 1, 'store_id': 1, 'name': 'Dichtertje' },
  { 'id': 2, 'store_id': 1, 'name': 'De uitvreter' },
  { 'id': 3, 'store_id': 2, 'name': 'Titaantjes' }
];
</code></pre>

<p>TypeScript is new to me, but I think I am close to making things work here.</p>

<p>(Also overwriting the original books array could be an option, then using <code>*ngFor="#book of books"</code>.)</p>

<p><strong>EDIT</strong>
Getting closer, but still giving an error.</p>

<pre class="lang-ts prettyprint-override"><code>//changes on top:
import {Component, Input, OnInit} from 'angular2/core';

// ..omitted

//changed component:
export class BookComponent implements OnInit {
  @Input() 
  store: Store;

  public books = BOOKS;

  // adding the data in a constructor needed for ngInit
  // "EXCEPTION: No provider for Array!"
  constructor(
    booksByStoreID: Book[];
  ) {}


  ngOnInit() {
    this.booksByStoreID = this.books.filter(
      book =&gt; book.store_id === this.store.id);
  }
}

// ..omitted
</code></pre>