回调函数中的变量可见性

Question

我做了这个函数直接在有用的数据结构中获取查询结果。问题在于：在第一个console.log（）调用中，在回调函数内部，stored_data var包含确切的结果，在第二个console.log（）调用stored_data变量看起来像未初始化。建议？ 代码如下：

function dojo_query_mysql(query_string) { 
     //The parameters to pass to xhrPost, the message, and the url to send it to 
     //Also, how to handle the return and callbacks. 
     var stored_data; 
    var raw_data = new Object; 
     var xhrArgs = { 
     url: "query.php", 
     postData: query_string, 
     handleAs: "text", 
     load: function(data) { 
      raw_data = dojo.fromJson(data); 
      stored_data = new dojo.data.ItemFileReadStore({data: raw_data}); 
    console.log(stored_data); 
     }, 
     error: function(error) { 
      //We'll 404 in the demo, but that's okay. We don't have a 'postIt' service on the 
      //docs server. 
      //stored_data = error; 
     } 
     } 
     //Call the asynchronous xhrPost 
     var deferred = dojo.xhrPost(xhrArgs); 
    console.log(stored_data); 
     return stored_data; 
    } 

Answer 1

我刚才记住的是，函数不会等待回调执行结束，为等待回调结束只是做了一点改变代码：

var xhrArgs = { 
     url: "query.php", 
sync: true, // THIS IS FORCE THE SYNCRONIZATION BETWEEN THE CALLBACK AND THE CODE 
     postData: query_string, 
     handleAs: "text", 
     load: function(data) { 
      raw_data = dojo.fromJson(data); 
      stored_data = new dojo.data.ItemFileReadStore({data: raw_data}); 
    console.log(stored_data); 
     }, 
     error: function(error) { 
      //We'll 404 in the demo, but that's okay. We don't have a 'postIt' service on the 
      //docs server. 
      //stored_data = error; 
     } 
     }