无法访问阵列的任何索引，但在完全登录时阵列能够正常工作

Question

我有一个函数foo，它接收一个名为locations的对象数组，并具有包含访问Foursquare API的信息的字符串fourSquareUrl。我从API获取数据并将其推送到locationData阵列。

当我尝试访问数组的索引locationData[i]时，我得到未定义的值。但是当我console.log（locationData）;该数组显示正确。谢谢你的帮助！

var locationData = []; 
function foo(locations) { 
    for (x in locations) { 
     var fourSquareUrl = 'API information'; 
     $.getJSON(fourSquareUrl, function(data) { 
       var foursquareLocation = data.response.venues; 
       if(foursquareLocation) { 
        var item = foursquareLocation[0]; 
        if (item) { 
         var address = item.location.formattedAddress; 
         locationData.push(address); 
        } 
        else { 
         var noAddress = "No location data available"; 
         locationData.push(noAddress); 
        } 
       } 
     }) 
    } 
} 

// works correctly 
console.log(locationData); 

// results in 'undefined' 
console.log(locationData[0]); 

Answer 1

检索到的地址可能是未定义的。如果是这种情况，您应该检查这种方式： var locationData = [];

function foo(locations) { 
    for (x in locations) { 
     var fourSquareUrl = 'API information'; 
     $.getJSON(fourSquareUrl, function(data) { 
       var foursquareLocation = data.response.venues; 
       if(foursquareLocation) { 
        var item = foursquareLocation[0]; 
        if (item) { 
         var address = item.location.formattedAddress; 
         if (!address) { 
          console.log('Empty address is returned'); 
         } 
         locationData.push(address); 
        } 
        else { 
         var noAddress = "No location data available"; 
         locationData.push(noAddress); 
        } 
       } 
     }) 
    } 
} 

// works correctly 
console.log(locationData); 

// results in 'undefined' 
console.log(locationData[0]);