AngularJS Example:

HTML

<div ng-app>
  <div ng-controller="CtrlA">
       <div ng-controller="CtrlB">
      gft   <select ng-model="selectedItem" ng-options="item for item in items">
         </select>
      </div>
  </div>
</div>

CSS

</style> <!-- Ugly Hack due to jsFiddle issue: http://goo.gl/BUfGZ --> 
<link rel="stylesheet" href="http://twitter.github.com/bootstrap/assets/css/bootstrap.css">
<script src="http://code.angularjs.org/1.0.3/angular.js"></script>
<style>
crfcccdxefgfggxffrdreeaA

JavaScript

function CtrlA($scope) {
  $scope.$watch(function watchA() {
    return { a: $scope.selectedItem};
  }, function(value) {
    if (value && value.a) console.log('A: ' + value.a);
  }, true);
  $scope.items = ['x', 'y'];
  $scope.selectedItem = $scope.items[0];
  console.log('A: ' + $scope.selectedItem);
}
function CtrlB($scope) {
  $scope.$watch(function watchB() {
    return { b: $scope.selectedItem};
  }, function(value) {
    if (value && value.b) console.log('B: ' + value.b);
  }, true);
}