title: Ionic2 function setInterval can't get a parameter
body: <p>I use Ionic2 to build an app,which based on Angular2 and Cordova.
  when I use function setInterval to get a parameter called clickCount,it occurt an undefine error.</p>
  
  <pre><code>export class ItemDetailsPage {
  static get parameters() {
      return [[NavController], [NavParams]];
  }
  constructor(nav, navParams) {
      this.nav = nav;
      this.clickCount = 0;
      this.selectedItem = navParams.get('item');
  }
  
  startTapped(event) {
     var cp= this.clickCount;   //here can get the clickCount
      this.stop = setInterval(function() {
          console.log(this.clickCount); //occur a undefined error
      }, 1000);
  }
  </code></pre>
  
  <p>}</p>
  
  <p><a href="https://i.stack.imgur.com/oFIu3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oFIu3.png" alt="the error"></a></p>