Ajax的小封装 get,post请求，ajax封装getpost,function Aja

Ajax的小封装 get,post请求，ajax封装getpost,function Aja

function Ajax() {    var xhr =null;     if(window.XMLHttpRequest) {         xhr = new XMLHttpRequest();     } else {         xhr = new ActiveXObject("Microsoft.XMLHttp");     }     this.get=function(url,success,fail){ //get请求         xhr.open("GET", "1.jsp",true);         xhr.onreadystatechange=function(){            if(xhr.readyState==4) {                alert(xhr.status);                if(xhr.status==200) {                    var txt = xhr.responseText;                     txt = eval("("+txt+")");                     var ch = txt.charAt(0);                        if(ch=="<") { //xml类型                            var xml = xhr.responseXML;                            success(eval("("+xml+")"));                        } else if(ch=="["||ch=="{") {//json类型                             txt = eval("("+txt+")");                             success(txt);                        } else {//不知道直接返回                            success(txt);                        }                } else {                     if(fail) {                         fail(xhr.status);                     }                }            }          };         xhr.send(null);     };     this.post = function (url,param,success,fail) {//post请求         xhr.open("POST", "1.jsp",true);         xhr.onreadystatechange=function(){            if(xhr.readyState==4) {                alert(xhr.status);                if(xhr.status==200) {                    var txt = xhr.responseText;                    var ch = txt.charAt(0);                    if(ch=="<") { //xml类型                        var xml = xhr.responseXML;                        success(eval("("+xml+")"));                    } else if(ch=="["||ch=="{") {//json类型                         txt = eval("("+txt+")");                         success(txt);                    } else {//不知道直接返回                        success(txt);                    }                } else {                     if(fail) {                         fail(xhr.status);                     }                }            }          };         xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");         xhr.send(param);     };}//该片段来自于http://byrx.net