title: setInterval, clearInterval instance out of scope
body: <p>In Ionic3, I made a interval that refresh my data and I want it to stop when leaving the view. But I've been unable to scope the interval instance...
  Note that this is my first step in typescript....</p>
  
  <pre><code>updateData(){    
    var interval = setInterval(() =&gt; {
      this.getdata.getData().subscribe( data =&gt; {
        this.channels = data.channels;
      })
    },2000);
  }
  
  ionViewWillLeave() {
    clearInterval(interval);//[TS]Cannot find name 'interval'
    console.log('leave view');
  }
  </code></pre>