title: How to find click event on header in angular js?
body: <p>I am using an angular ui grid .
  <a href="http://ui-grid.info/docs/#/tutorial/102_sorting" rel="nofollow">http://ui-grid.info/docs/#/tutorial/102_sorting</a>
  I want to show an alert when I click the header icon <code>V</code> . Currently it is showing <code>hello</code> text when I click the <code>v</code> icon. Can I show an alert when I click the icon?</p>
  
  <p>Here is my code:
  <a href="http://plnkr.co/edit/UAElQb8dl9qr5Cwmjg6q?p=preview" rel="nofollow">http://plnkr.co/edit/UAElQb8dl9qr5Cwmjg6q?p=preview</a></p>
  
  <pre><code> $http.get('https://cdn.rawgit.com/angular-ui/ui-grid.info/gh-pages/data/100.json')
      .success(function(data) {
        $scope.gridOptions1.data = data;
      });
  </code></pre>