title: How to $watch multiple variable change in angular
body: <p>How to <code>$scope.$watch</code> multiple variables in Angular, and trigger callback when one of them has changed.</p>
  
  <pre><code>$scope.name = ...
  $scope.age = ...
  $scope.$watch('???',function(){
      //called when name or age changed
  })
  </code></pre>