title: angular 2: concat arrays in a pipe without loosing databinding
body: <p>I have a simple pipe:</p>
  
  <pre><code>export class MergePipe implements PipeTransform {
  transform(first: any[], second: any[], order: Boolean): any {
      return order ? first.concat(second):second.concat(first);
  }
  </code></pre>
  
  <p>Which I'm using on a simple button: <code>&lt;button *ngFor="let item of items | sort:suffix | filter:filterargs | merge:newItems:false"&gt;&lt;/button&gt;</code>.</p>
  
  <p>And then push some values into the newItems with newItems.push(values) but nothing happens. If I remove the pipe from *ngFor, I receive the expected changes.</p>
  
  <p>I think I missunderstand something on how the databinding is working. </p>
  
  <p>Thanks for any helpful information.</p>