Dojo 回调函数中的可变可见性

我使用此函数直接在有用的数据结构中获取查询结果。问题如下：在第一个console.log（）调用中，在回调函数内部，存储的_数据变量包含确切的结果，在第二个console.log（）调用中，存储的_数据变量看起来没有初始化。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;
    }

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;
        }
      }

---

我刚刚记住，函数不会等待回调执行结束，因为等待回调结束只需对代码做一点更改：

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;
    }

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;
        }
      }

除非绝对必要，否则绝对不要使用

sync:true

。它挫败了XHR的许多目的，并从AJAX中获得了第一个好处。理想情况下，依赖XHR结果的任何代码都应该在

加载

回调中，或者使用

然后

（或者Dojo<1.5中的

添加回调

）添加到以后的回调中。