XHR request factory, only does the feature detection once and generates a dedicated function

factory.js

 util.request = (function(){
    var fn = {
        body: 'return null'
      };
    
    if ('XDomainRequest' in window){
      fn.body = 'return new XDomainRequest();';
      fn.xdomain = true;
    } else if ('XMLHttpRequest' in window) {
      fn.body = 'return new XMLHttpRequest();';
      fn.xdomain = util.ua.hasCORS;
    } else if ('ActiveXObject' in window) {
      try {
        new ActiveXObject('MSXML2.XMLHTTP');
        fn.body = 'return new ActiveXObject("MSXML2.XMLHTTP");';
      } catch(e) {
        try {
          new ActiveXObject('Microsoft.XMLHTTP');
          fn.body = 'return new ActiveXObject("Microsoft.XMLHTTP");';
        } catch (e) {}
      }
    }

    return new Function('xdomain', fn.xdomain ? fn.body : 'if(xdomain)return null;' + fn.body);
  }());