多浏览器处理XMLHttpRequest对象

在Ajax中我们用到XMLHttpRequest对象，对于不同浏览器之间是否对XMLHttpRequest对象同时兼容需要我们作出处理

        var xmlhttprequest = false;
        function createXMLHttpRequest() {
            try {
                xmlhttprequest = new ActiveXObject("Msxml2.XMLHTTP");
            }
            catch (e1) { 
                try
                {
                    xmlhttprequest=new ActiveXObject("Microsoft.XMLHTTP");
                }
                catch()
                {
                    xmlhttprequest=false;
                }
            }
            
            if(!xmlhttprequest && typeof XMLHttpRequest!='undefined')
            {
                xmlhttprequest=new XMLHttpRequest();
            }
        }