angularjs三级联动

<div ng-controller="AjaxCtrl">
      <h1>AJAX - Oriented</h1>
    <div>
        Country: 
        <select id="country" ng-model="country" ng-options="country for country in countries">
          <option value=''>Select</option>
        </select>
    </div>
    <div>
        City: <select id="city" ng-disabled="!cities" ng-model="city" ng-options="city for city in cities"><option value=''>Select</option></select>
    </div>
    <div>
        Suburb: <select id="suburb" ng-disabled="!suburbs" ng-model="suburb" ng-options="suburb for suburb in suburbs"><option value=''>Select</option></select>        
    </div>
</div>
  <div ng-controller="StaticCtrl">
      <h1>Static - Oriented</h1>
      <p>This approach may be better when you have the entire dataset</p>
    <div>
        Country: 
        <select id="country" ng-model="cities" ng-options="country for (country, cities) in countries">
          <option value=''>Select</option>
        </select>
    </div>
    <div>
        City: <select id="city" ng-disabled="!cities" ng-model="suburbs" ng-options="city for (city, suburbs) in cities"><option value=''>Select</option></select>
    </div>
    <div>
        Suburb: <select id="suburb" ng-disabled="!suburbs" ng-model="suburb" ng-options="suburb for suburb in suburbs"><option value=''>Select</option></select>        
    </div>
  </div>

js

function AjaxCtrl($scope) {
    $scope.countries = ['usa', 'canada', 'mexico', 'france'];
    $scope.$watch('country', function(newVal) {
        if (newVal) $scope.cities = ['Los Angeles', 'San Francisco'];
    });
    $scope.$watch('city', function(newVal) {
        if (newVal) $scope.suburbs = ['SOMA', 'Richmond', 'Sunset'];
    });
}

function StaticCtrl($scope) {
    $scope.countries = {
        'usa': {
            'San Francisco': ['SOMA', 'Richmond', 'Sunset'],
            'Los Angeles': ['Burbank', 'Hollywood']
        },
        'canada': {
            'People dont live here': ['igloo', 'cave']
        }
    };
}