如何在Angular 1.x.x中添加预先填充的国家、州和城市列表

[
  {
    "country": "中国",
    "states": [
      {
        "state": "北京市",
        "cities": ["北京市"]
      },
      {
        "state": "上海市",
        "cities": ["上海市"]
      }
    ]
  },
  {
    "country": "美国",
    "states": [
      {
        "state": "纽约州",
        "cities": ["纽约市", "布鲁克林市"]
      },
      {
        "state": "加利福尼亚州",
        "cities": ["洛杉矶市", "旧金山市"]
      }
    ]
  }
]

app.service('LocationService', function($http) {
  var countries = [];

  this.getCountries = function() {
    return $http.get('path/to/countries.json').then(function(response) {
      countries = response.data;
      return countries;
    });
  };

  this.getStatesByCountry = function(country) {
    var selectedCountry = countries.find(function(c) {
      return c.country === country;
    });

    return selectedCountry ? selectedCountry.states : [];
  };

  this.getCitiesByState = function(country, state) {
    var selectedCountry = countries.find(function(c) {
      return c.country === country;
    });

    if (selectedCountry) {
      var selectedState = selectedCountry.states.find(function(s) {
        return s.state === state;
      });

      return selectedState ? selectedState.cities : [];
    }

    return [];
  };
});

app.controller('LocationController', function($scope, LocationService) {
  $scope.countries = [];
  $scope.states = [];
  $scope.cities = [];

  LocationService.getCountries().then(function(countries) {
    $scope.countries = countries;
  });

  $scope.onCountryChange = function() {
    $scope.states = LocationService.getStatesByCountry($scope.selectedCountry);
    $scope.cities = [];
  };

  $scope.onStateChange = function() {
    $scope.cities = LocationService.getCitiesByState($scope.selectedCountry, $scope.selectedState);
  };
});

<select ng-model="selectedCountry" ng-options="country.country for country in countries" ng-change="onCountryChange()">
  <option value="">选择国家</option>
</select>

<select ng-model="selectedState" ng-options="state.state for state in states" ng-change="onStateChange()">
  <option value="">选择州</option>
</select>

<select ng-model="selectedCity" ng-options="city for city in cities">
  <option value="">选择城市</option>
</select>