title: Angular 5, Passing table of tags to pipe filter
body: <p>I'm new in angular so please be lenient :-)
  I'm working with angular 5 and I can't find a way to filter array of objects using array of tags.
  I'm trying to pass array of tags ty my custom pipe, unfortunately it doesn't work.
  My code looks like this:</p>
  
  <p><strong>Component</strong></p>
  
  <pre><code>*export class StarsComponent implements OnInit {
  ....
  tagFilter: string[];
  ....
  }*
  </code></pre>
  
  <p><strong>Pipe</strong></p>
  
  <pre><code>*@Pipe({
  name: 'filterByTag'
  })
  export class FilterByPipe implements PipeTransform {
  
      transform(items: any[], prop: string, tags: string[]): any {
      console.log('filterByTag items - ', items);
      console.log('filterByTag prop - ', prop);
      console.log('filterByTag tags - ', tags);
      return items;
  }*
  </code></pre>
  
  <p><strong>View</strong></p>
  
  <pre><code>**&lt;div&gt;
  &lt;button type="button" class="btn btn-default" *ngFor="let tag of uniqTags"
      (click)="addTagToFilter(tag)" [ngClass]="{'btn-primary': (tagFilter.indexOf(tag) != -1)}"&gt;
      {{tag}}
  &lt;/button&gt;
  &lt;/div&gt;
  &lt;ul class="stars"&gt;
  &lt;li *ngFor="let starE of allstars | filterByTag: 'tagFilter': tagFilter"&gt; 
  ....
  &lt;/li&gt;
  </code></pre>
  
  <p>**</p>
  
  <p>My console looks like this:</p>
  
  <pre><code>filterByTag items -  {array of my items} - it's OK
  filterByTag prop -  tagFilter - it's OK
  filterByTag tags -**it's empty, why?**
  </code></pre>
  
  <p>Is there any way to pass array of string tags to FilterByPipe ?
  Thanks</p>