A polyfill for CORS in older versions of IE.

ie-cors-polyfill.js

var xhr2 = false;
try { xhr2 = 'useCredentials' in new XMLHttpRequest; } catch (e) {}
var old = window.XMLHttpRequest;
function XMLHttpRequest() {
  if (xhr2) return new old();
}
XMLHttpRequest.prototype.open = function(method, url, async, user, pass) {
  var pageOrigin = location.protocol + ':' + location.host;
  var self = this;
  function wrap(m) {
    xhr[m] = function() {
      for (var i in xhr) if (typeof xhr[i] !== 'function') {
        try { self[i] = xhr[i]; } catch (e) {}
      }
      if (fn) fn();
      if (self[m]) self[m].apply(self, arguments);
    };
  }
  var xhr;
  if (url && /^https?:\/\//i.test(url) && url.indexOf(host)!==0 && self.XDomainRequest) {
    xhr = new XDomainRequest();
    wrap('onload', function() {
      self.readyState = 4;
      if (self.onreadystatechange) self.onreadystatechange();
    });
    wrap('onerror', function() {
      self.readyState = 4;
      if (self.onreadystatechange) self.onreadystatechange();
    });
  }
  else {
    xhr = new old();
    wrap('onreadystatechange', function() {
      if (xhr.readyState===4) {
        if (xhr.status && xhr.status <400 && xhr.status >= 200) {
          if (self.onload) self.onload();
        }
        else if (self.onerror) self.onerror(Error(0));
      }
    };
  }
  this._xhr = xhr;
  xhr.timeout = self.timeout;
  wrap('onprogress');
  wrap('ontimeout');
  xhr.open(method, url, async, user, pass); 
};
XMLHttpRequest.prototype.abort = function(){
  this._xhr.abort();
};
XMLHttpRequest.prototype.getAllResponseHeaders = function() {
  try { return this._xhr.getAllResponseHeaders(); } catch (e) {}
};
XMLHttpRequest.prototype.getResponseHeaders = function() {
  try { return this._xhr.getResponseHeaders(); } catch (e) {}
};
XMLHttpRequest.prototype.send = function() {
  setTimeout(function (x) { x.send(); }, 0, this._xhr); 
};