Javascript中嵌套函数的返回值 [英] Return value from nested function in Javascript

问题描述

我有一个功能设置如下

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

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

根据我的逻辑，该警报应该返回foo"，但它返回未定义.我做错了什么?

To my logic, that alert should return 'foo', but instead it returns undefined. What am I doing wrong?

更新:这是我的实际代码(这是一个使用 Google API 进行反向地理编码的函数)

UPDATE: Here's my actual code (it's a function for reverse-geocoding with the Google API)

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;
    });   
   }

推荐答案

你必须先调用一个函数，然后它才能返回任何东西.

you have to call a function before it can return anything.

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

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

或者:

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

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

用于您的实际代码.返回应该在外部，在主函数中.回调在 getLocations 方法内的某处被调用，因此它的返回值不会在您的主函数内收到.

for your actual code. The return should be outside, in the main function. The callback is called somewhere inside the getLocations method and hence its return value is not recieved inside your main function.

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
   }

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