CORS with jQuery and XDomainRequest in IE8/9
UPDATE: I highly recommend not investing any time in XDomainRequest, because it is a terribly poor implementation with many limitations. It basically only really works for GET requests to non-ssl servers, so you might as well use jsonp or whatever.
I am using CORS to call a cross domain API, however Internet Explorer is giving issues. CORS should be possible in IE8 and IE9 through the XDomainRequest object, however I can't get things to work..
JQuery refuses to provide native support for XDomainRequest, however several jQuery plugins are suggested to add this support. This topic suggest two such plugins: jQuery.XDomainRequest.js and xdr.js, which has been reported to work. Afaik, the plugins should automatically override behavior of jQuery.ajax. I found another plugin here.
I put a little demo pages with the respective plugins jQuery.XDomainRequest and xdr and jquery.ie.cors that perform ajax requests to a CORS enabled server. The pages are working in Chrome and Firefox, however IE8/9 instantly throw a permission denied error (even before making the request). This MSDN post suggest adding another handler xhr.onprogress = function() {}; but I tried this and it isn't working either.
Any clues what I am doing wrong? I have also tested with IE8 now using MS virtual server, but it has exactly the same problem.
Edit: OK so I figured out that part of the problem was that I was using POST over HTTPS. Apparently XDomainRequest does not allow CORS over HTTPS. I can switch to HTTP but I really need POST.
Edit2: See this issue on github for the end of this story. It turns out that when using HTTP POST, the xDomainRequest can only encode the request body (arguments) as text/plain. This pretty much makes it worthless, because everyone uses application/x-www-form-urlencoded or multipart/form-data.
Answer
POST method is supported, and to make a cross-domain https:// request your calling page would also need to be loaded over https. This is the best article I have found which explains these and other limitations of XDomainRequest in detail: