title: Pipes Angular 2 dynamic Array Length
body: <p>Is it posible to dynamically show length of array by using pipe? Here's my code:</p>
  
  <pre><code>import { Pipe, PipeTransform } from '@angular/core';
  
  @Pipe({
    name: 'lengthOfArray'
  })
  export class LengthOfArrayPipe implements PipeTransform {
  
    transform(value: any): number {
      return value.length;
    }
  
  }
  </code></pre>
  
  <p>I use it like this:</p>
  
  <p><strong>Component</strong></p>
  
  <pre><code>listOfIdToExport: any[] = [];
  </code></pre>
  
  <p><strong>Template</strong></p>
  
  <pre><code>Element numer: {{ listOfIdToExport | lengthOfArray }}
  </code></pre>
  
  <p>I have a function which adds or removes elements from this array and problem is that pipe doesn't update array length when change occurs.</p>