ajax js兼容语法

  function xhr(){

        //封装通用的xhr对象兼容各个版本(针对ie7 fireox )

       //判断浏览器是否将XMLHttpRequest作为本地对象实现，

        if(typeof XMLHttpRequest !="undefined"){

            //typeof 返回该对象的类型 如果浏览器不支持则返回的是undefined

            return new XMLHttpRequest();

        }else if(typeof ActiveXObject != "undefined"){

            将所有可能出现的ActiveXObject版本放在一个数组中

            var xhrArr = ['Microsoft.XMLHTTP','MSXML2.XMLHTTP.6.0',

            'MSXML2.XMLHTTP.5.0','MSXML2.XMLHTTP.4.0',

            'MSXML2.XMLHTTP.3.0','MSXML2.XMLHTTP.2.0']

            //遍历创建XMLHttpRequest对象

            var len = xhr.length;

            for(var i = 0; i < len; i++ ){

                try{

                    xhr = new ActiveXOject[xhrArr[i]];

                    break;

                }

                catch(ex){

                    null;

                }

            } return xhr;

        }else{

            throw new Error('No XHR object availabel.')

        }

}

简易兼容语法

   var ajax = null;     

   if (window.XMLHttpRequest) {           

            //code for ie7+ Firefox Chrome Opera Safari

             ajax = new XMLHttpRequest();      

  } else {          

                //code for IE6 IE5               

                ajax = new ActiveXObject("Microsoft.XMLHTTP")       

 }      

 console.log(ajax);