XHR同步調用在Chrome中失敗。不等待xhr響應的腳本

Question

問題：在Chrome中工作時，腳本未等待同步xhr響應。在FireFox/IE中正常工作。已經使用onreadyStateHandlers，但仍然在收到響應之前執行其他代碼。

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; 

} 

請分享您的想法！

Answer 1

函數callServer（）不等待請求被響應。使用回調來解決這個問題：

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; 

}