XHR同步调用在Chrome中失败。不等待xhr响应的脚本

Question

问题：在Chrome中工作时，脚本未等待同步xhr响应。在FireFox/IE中正常工作。已经使用onreadyStateHandlers，但仍然在收到响应之前执行其他代码。

function callingScript() 
{ var a=callServer(); 
    alert(a);//Here a is showing undefined while executing in chrome. 
      But in FF/IE its waiting for the response and then alerts a with response. 
} 

function callServer() 
{ 
var response; 
var httpRequest = new XMLHttpRequest(); 
httpRequest.open("POST","abc",false); 
httpRequest.setRequestHeader('Content-Type','application/x-www-form-urlencoded'); 
httpRequest.onreadystatechange = function() 
    {  
     if (httpRequest.readyState != 4) 
      {return; } 

     if (httpRequest.status != 200)  
       {response=httpRequest.status;} 
     else {response=httpRequest.responseText;} 

    }; 
httpRequest.send(data); 
return response; 

} 

请分享您的想法！

Answer 1

函数callServer（）不等待请求被响应。使用回调来解决这个问题：

function callingScript() 
{ callServer(function(response) { 
     alert(response); 
    }); 
} 

function callServer(callback) 
{ 
var response; 
var httpRequest = new XMLHttpRequest(); 
httpRequest.open("POST","abc",false); 
httpRequest.setRequestHeader('Content-Type','application/x-www-form-urlencoded'); 
httpRequest.onreadystatechange = function() 
    {  
     if (httpRequest.readyState != 4) 
      {return; } 

     if (httpRequest.status != 200)  
       {response=httpRequest.status;} 
     else {response=httpRequest.responseText;} 

     callback(response); 
    }; 
httpRequest.send(data); 
return response; 

}