Javascript 中嵌套函数的返回值[重复]

我有一个设置如下的函数

function mainFunction() {
      function subFunction() {
            var str = "foo";
            return str;
      }
}

var test = mainFunction();
alert(test);

按照我的逻辑，该警报应该返回“foo”，但它返回未定义。我究竟做错了什么？

UPDATE：这是我的实际代码（它是使用 Google API 进行反向地理编码的函数）

function reverseGeocode(latitude,longitude){
    var address = "";
    var country = "";
    var countrycode = "";
    var locality = "";

    var geocoder = new GClientGeocoder();
    var latlng = new GLatLng(latitude, longitude);

     return geocoder.getLocations(latlng, function(addresses) {
     address = addresses.Placemark[0].address;
     country = addresses.Placemark[0].AddressDetails.Country.CountryName;
     countrycode = addresses.Placemark[0].AddressDetails.Country.CountryNameCode;
     locality = addresses.Placemark[0].AddressDetails.Country.AdministrativeArea.SubAdministrativeArea.Locality.LocalityName;
     return country;
    });   
   }

你必须先调用一个函数，然后它才能返回任何内容。

function mainFunction() {
      function subFunction() {
            var str = "foo";
            return str;
      }
      return subFunction();
}

var test = mainFunction();
alert(test);

Or:

function mainFunction() {
      function subFunction() {
            var str = "foo";
            return str;
      }
      return subFunction;
}

var test = mainFunction();
alert( test() );

对于您的实际代码。返回应该在主函数之外。回调在内部某处被调用getLocations方法，因此它的返回值不会在您的主函数中收到。

function reverseGeocode(latitude,longitude){
    var address = "";
    var country = "";
    var countrycode = "";
    var locality = "";

    var geocoder = new GClientGeocoder();
    var latlng = new GLatLng(latitude, longitude);

    geocoder.getLocations(latlng, function(addresses) {
     address = addresses.Placemark[0].address;
     country = addresses.Placemark[0].AddressDetails.Country.CountryName;
     countrycode = addresses.Placemark[0].AddressDetails.Country.CountryNameCode;
     locality = addresses.Placemark[0].AddressDetails.Country.AdministrativeArea.SubAdministrativeArea.Locality.LocalityName;
    });   
    return country
   }