1// browser shim for xmlhttprequest module
 2var hasCORS = require('has-cors');
 3
 4module.exports = function(opts) {
 5  var xdomain = opts.xdomain;
 6
 7  // scheme must be same when usign XDomainRequest
 8  // http://blogs.msdn.com/b/ieinternals/archive/2010/05/13/xdomainrequest-restrictions-limitations-and-workarounds.aspx
 9  var xscheme = opts.xscheme;
10
11  // XDomainRequest has a flow of not sending cookie, therefore it should be disabled as a default.
12  // https://github.com/Automattic/engine.io-client/pull/217
13  var enablesXDR = opts.enablesXDR;
14
15  // XMLHttpRequest can be disabled on IE
16  try {
17    if ('undefined' != typeof XMLHttpRequest && (!xdomain || hasCORS)) {
18      return new XMLHttpRequest();
19    }
20  } catch (e) { }
21
22  // Use XDomainRequest for IE8 if enablesXDR is true
23  // because loading bar keeps flashing when using jsonp-polling
24  // https://github.com/yujiosaka/socke.io-ie8-loading-example
25  try {
26    if ('undefined' != typeof XDomainRequest && !xscheme && enablesXDR) {
27      return new XDomainRequest();
28    }
29  } catch (e) { }
30
31  if (!xdomain) {
32    try {
33      return new ActiveXObject('Microsoft.XMLHTTP');
34    } catch(e) { }
35  }
36}