IE9 JQuery.ajax throws mystery error

Question

I'm experiencing a difficult ajax error in IE9. I will say up-front that this is not technically a cross-domain request so I'm sure that is not the problem.

Edit: It appears that the problem may be related to a same-domain request being treated as cross-domain, though it is not clear why (see comments).

I'm using a local proxy to make cross-domain ajax requests, and the url I use looks like http://localhost/proxy/?target=..... All good browsers are happy with this but IE immediately returns an error before the request is even dispatched (I have verified this using Fiddler and IE's developer tools network capture).

When I inspect the error object passed to JQuery's ajax.error callback its isRejected() function returns true, but I can't find out what would cause a request to be rejected. The error object's readyState is 4 (implying the request is complete?), status is 0 and statusText is "error".

I'm building my request a bit like this:

$.ajax(url, {
    data: {...list of parameters...},
    dataType: 'json',
    type: 'GET',
    success: function() { ... },
    error: function() { ... },
    beforeSend: proxy.beforeRequestSend,
    timeout: 35000
});

The proxy.beforeRequestSend function looks like this:

this.beforeRequestSend = function(XHR, settings) {

  if(that.proxyRequired(settings.url)) {
    // I've also tried using the full url (http://localhost/proxy/?...)
    settings.url = 'proxy/?target=' + encodeURIComponent(settings.url); 
  }
};

Does anyone know what would cause the request to fail outright in IE9? Unfortunately I don't have access to IE8 or 7 for testing but I assume they would behave the same. The fact that JQuery's ajax error handler is invoked suggests that the error is not occuring while I am building the request, but when it is supposedly executed. All other browsers working correctly tells me that the fundamentals are correct.

I have previously read that the JQuery / IE combo has issues url-encoding some characters, but if I alert settings.url at the end of the beforeSend function the target URL is correctly encoded (this also tells me that that.proxyRequired(settings.url) returns true).

Any input much appreciated.

Use the unminimized version of jquery and step into the call. — asawyer, Dec 20 '11 at 21:49
@asawyer I spent a while wading through the JQuery, and as far as I can tell both firefox & IE think that my request is cross-domain (??) but as IE returns false for `JQuery.support.cors` where Firefox returns true this is where they diverge. If this is the issue I don't konw why either browser thinks the request is cross-domain, when I even tested giving the full proxy url (with domain) and stripped 'http://' from the target url — tomfumb, Dec 20 '11 at 22:48

score 3 · Answer 1 · edited Feb 15 '12 at 05:42

3

In your javascript, before you invoke $.ajax (or equivalent) force cross domain behavior:

JQuery.support.cors=true;

edited Feb 15 '12 at 05:42

Peter O.

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answered Feb 15 '12 at 05:08

spockmonster

31
4

score 1 · Answer 2 · edited May 23 '17 at 11:56

1

Is your proxy action sending out a redirect in response to the ajax call? Browsers silently follow the redirects and that might be the reason why XHR is detecting the XSS attempt. Since jQuery does not support CORS on IE9, you're left with the error.

See this other Stackoverflow question: Cross-origin Ajax requests don't work in Opera and IE9?

edited May 23 '17 at 11:56

Community

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answered Dec 21 '11 at 00:08

lsoliveira

4,560
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good suggestion but no, the proxy is not redirecting - as I said above the request never even leaves IE. – tomfumb Dec 21 '11 at 00:31

score 1 · Accepted Answer · answered Dec 31 '11 at 03:07

As you can see in my question's code I am prepending the proxy url in the JQuery.ajax function's beforeSend callback (proxy.beforeRequestSend). By the time this function is executed JQuery has already inspected the request and decided that is it cross-domain.

As a result JQuery was treating all my requests as cross-domain, even though they all went to the local proxy. JQuery then rejected any cross-domain request in IE and Opera because they don't support CORS.

Fortunately the crossDomain property is passed to the beforeSend callback in the settings object and is easily changed.

this.beforeRequestSend = function(XHR, settings) {

  if(that.proxyRequired(settings.url)) {
    settings.url = 'proxy/?target=' + encodeURIComponent(settings.url);
    settings.crossDomain = false;
  }
};

IE9 JQuery.ajax throws mystery error

3 Answers3