XMLHttpRequest 状态 0（响应文本为空）

Question

Cannot get data with XMLHttpRequest (status 0 and responseText is empty):

xmlhttp=new XMLHttpRequest();
xmlhttp.open("GET","http://www.w3schools.com/XML/cd_catalog.xml", true);
xmlhttp.onreadystatechange=function() 
{
  if(xmlhttp.readyState==4)
    alert("status " + xmlhttp.status);
}
xmlhttp.send();

It alerts "status 0".

The same situation with the localhost request (cd_catalog.xml is saved as a local file)

xmlhttp.open("GET","http://localhost/cd_catalog.xml", true);

But with the localhost IP request

xmlhttp.open("GET","http://127.0.0.1/cd_catalog.xml", true);

and with the local file request

xmlhttp.open("GET","cd_catalog.xml", true);

everything is OK (status 200)

What can cause the problem (status=0) with the online request?

PS: Live HTTP Headers shows that everything is OK in all 4 cases:

HTTP/1.1 200 OK
  Content-Length: 4742

PS2: Apache local web server on VMWare (host OS Win7, Guest OS Ubuntu, Network adapter – NAT). Browser – Firefox.

Answer 1

status is 0 when your html file containing the script is opened in the browser via the file scheme. Make sure to place the files in your server (apache or tomcat whatever) and then open it via http protocol in the browser. (ie http://localhost/myfile.html ) This is the solution.

Answer 2

The cause of your problems is that you are trying to do a cross-domain call and it fails .

If you're doing localhost development you can make cross-domain calls - I do it all the time.

For Firefox, you have to enable it in your config settings

signed.applets.codebase_principal_support = true

Then add something like this to your XHR open code:

  if (isLocalHost()){
    if (typeof(netscape) != 'undefined' && typeof(netscape.security) != 'undefined'){
      netscape.security.PrivilegeManager.enablePrivilege('UniversalBrowserRead');
    }
  }

For IE, if I remember right, all you have to do is enable the browser's Security setting under "Miscellaneous → Access data sources across domains" to get it to work with ActiveX XHRs.

IE8 and above also added cross-domain capabilities to the native XmlHttpRequest objects, but I haven't played with those yet.

Answer 3

实际上确保您的按钮类型是按钮不是提交，这导致了我最近遇到的状态冲突。

Answer 4

If the server responds to an OPTIONS method and to GET and POST (whichever of them you're using) with a header like:

Access-Control-Allow-Origin: *

It might work OK. Seems to in FireFox 3.5 and rekonq 0.4.0. Apparently, with that header and the initial response to OPTIONS, the server is saying to the browser, "Go ahead and let this cross-domain request go through."

Answer 5

Consider also the request timeout :

Modern browser return readyState=4 and s tatus=0 if too much time passes before the server response.

Answer 6

将setRequestHeader("Access-Control-Allow-Origin","*")到您的服务器响应中。

Answer 7

Open javascript console . You'll see an error message there. In my case it was CORS.

Answer 8

I had faced a similar problem. Every thing was okay, the "readystate" was 4, but the "status" was 0. It was because I was using a Apache PHP portable server and my file in which I used the "XMLHttpRequest" object was a html file. I changed the file extension to php and the problem was solved.

Answer 9

要回答为什么http://127.0.0.1/cd_catalog.xml有效而http://localhost/cd_catalog.xml无效的问题：Firefox 将 127.0.0.1 和 localhost 视为两个不同的域。

Answer 10

To see what the problem is, when you get the cryptic error 0 go to ... | More Tools | Developer Tools (Ctrl+Shift+I) in Chrome (on the page giving the error)

Read the red text in the log to get the true error message. If there is too much in there, right-click and Clear Console, then do your last request again.

My first problem was, I was passing in Authorization headers to my own cross-domain web service for the browser for the first time.

I already had:

Access-Control-Allow-Origin: *

But not:

Access-Control-Allow-Methods: GET, POST, PUT, DELETE
Access-Control-Allow-Headers: Authorization

in the response header of my web service.

After I added that, my error zero was gone from my own web server, as well as when running the index.html file locally without a web server, but was still giving errors in code pen.

Back to ... | More Tools | Developer Tools while getting the error in codepen, and there is clearly explained: codepen uses https, so I cannot make calls to http, as the security is lower.

I need to therefore host my web service on https.

Knowing how to get the true error message - priceless!

Answer 11

Here's another case in which status === 0 , specific to uploading:

If you attach a 'load' event handler to XHR.upload , as suggested by MDN (scroll down to the upload part of 'Monitoring progress'), the XHR object will have status=0 and all the other properties will be empty strings. If you attach the 'load' handler directly to the XHR object, as you would when downloading content, you should be fine (given you're not running off localhost).

However, if you want to get good data in your 'progress' event handlers, you need to attach a handler to XHR.upload , not directly to the XHR object itself.

I've only tested this so far on Chrome OSX, so I'm not sure how much of the problem here is MDN's documentation and how much is Chrome's implementation...

Answer 12

Alex Robinson already (and first) gives the correct answer to this issue. But to elaborate it a little more...

You must add the HTTP response header:

Access-Control-Allow-Origin: *

If you do this, the result is not just 'might work', but 'will work'.

NB What you need to add is an HTTP response header - so you can only do this on a server which you control. It will never be possible to directly fetch http://w3schools.com/XML/cd_catalog.xml from its original URL using an XMLHttpRequest (as per OP's question), because that resource does not (at least, not as of 24 Apr 2015) include any such CORS header.

http://en.wikipedia.org/wiki/Cross-origin_resource_sharing gives more info.

Answer 13

My problem similar to this was solved by checking my html code. I was having an onclick handler in my form submit button to a method. like this : onclick="sendFalconRequestWithHeaders()" . This method in turn calls ajax just like yours, and does what I want. But not as expected, my browser was returning nothing.

Learned From someone's hardwork , I have returned false in this handler, and solved. Let me mention that before arriving to this post, I have spent a whole 3-day weekend and a half day in office writing code implementing CORS filters , jetty config , other jersey and embedded jetty related stuff - just to fix this., revolving all my understanding around cross domain ajax requests and standards stuff. It was ridiculous how simple mistakes in javascript make you dumb.

To be true, I have tried signed.applets.codebase_principal_support = true and written isLocalHost() **if** . may be this method needs to be implemented by us, firefox says there is no such Now I have to clean my code to submit git patch cleanly. Thanks to that someone.

Answer 14

A browser request "127.0.0.1/somefile.html" arrives unchanged to the local webserver, while "localhost/somefile.html" may arrive as "0:0:0:0:0:0:0:1/somefile.html" if IPv6 is supported. So the latter can be processed as going from a domain to another.

Answer 15

Alex Robinson and bmju provided valuable information to understand cross-origin issues. I wanted to add that you may need to make an explicit OPTIONS call in your client code before making the desired GET/POST (eg against a CORS OAuth service endpoint). Your browser/library may not automatically handle the OPTIONS request. Gruber, this is one of the possible answers to your question.

Answer 16

I had the same problem (readyState was 4 and status 0) , then I followed a different approach explained in this tutorial: https://spring.io/guides/gs/consuming-rest-jquery/

He didn't use XMLHttpRequest at all, instead he used jquery $.ajax() method:

<head>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
    <script src="hello.js"></script>
</head>

<body>
    <div>
        <p class="greeting-id">The ID is </p>
        <p class="greeting-content">The content is </p>
    </div>
</body>

and for the public/hello.js file (or you could insert it in the same HTML code directly):

$(document).ready(function() 
 {
    $.ajax({
        url: "http://rest-service.guides.spring.io/greeting"
   }).then(function(data) {
      $('.greeting-id').append(data.id);
      $('.greeting-content').append(data.content);
   });
 });

Answer 17

我不得不将我当前的 IP 地址（再次）添加到Atlas MongoDB 白名单，因此摆脱了 XMLHttpRequest status 0 错误

Answer 18

bottle app in python:

@route('/mazer2/get', method='POST')
def GetMaze2():
    if MazeCore == None: abort(666, "MazeCore поломался :///")
    Check()
    Comm = request.body.read().decode("utf-8")
    Map = MazeCore.GetMaze2(Comm, TestToken2())
    response.headers["Access-Control-Allow-Origin"] = "*" #Here ;'-} It helped me
    return Map

Answer 19

I had the same problem when I tried to consume some web methods created by python in a flask environment, by XMLHttpRequest. After inspecting the firefox console, I realised that the cause of problem was Same Origin Policy, which prevents calling web methods of a different ORIGIN (An Origin consists of a 3 part tuple including: protocol, domain, and port number). For me, the solution was to use CORS , and fortunately there is a python package named flask-cors which I used and everything works fine.

Answer 20

我刚刚遇到这个问题，因为我使用0.0.0.0作为我的服务器，将其更改为localhost并且它可以工作。

Answer 21

setRequestHeader("Access-Control-Allow-Origin","*") 在您的清单中

Answer 22

Edit: Please read Malvolio's comments below as this answer's knowledge is outdated.

You cannot do cross-domain XMLHttpRequests.

The call to 127.0.0.1 works because your test page is located at 127.0.0.1 , and the local test also works since, well... it's a local test.

The other two tests fail because JavaScript cannot communicate with a distant server through XMLHttpRequest.

You might instead consider either:

• XMLHttp-request your own server to fetch your remote XML content for you (php script, for example)
• Trying to use a service like GoogleAppEngine if you want to keep it full JavaScript.

Hope that helps