学习javascript对象碰到的问题 很急

Question

function ajax()
    {
        var xmlhttp=createXMLHttp();
        this.url_str='';//php后台文件
        this.div_id='';//加载的图层id
        this.str='';//传送的数据
        this.cc=function()
            {
                xmlhttp.onreadystatechange=function ()
                    {
                        if(xmlhttp.readyState==4)
                            {
                                alert(this.str);//注意这边弹出 这边弹出undefine
                                document.getElementById(this.div_id).innerHTML=xmlhttp.responseText;
                                document.getElementById("newDrag").style.display="block";
                            }
                            
                            
                    }
                xmlhttp.open('POST',this.url_str,true);
                xmlhttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
                xmlhttp.send(this.str);
                alert(this.str);//这里弹出正常
            }
    }function character_ajax(user_id,type,mission_id)
    {
        var aa=new ajax();
        aa.url_str='character.php';
        aa.div_id="newBody";
        aa.str="user_id="+user_id+'&type='+type
        aa.cc(); //弹出的是undefine
    }
为什么弹出个undefine  要如何解决 先谢谢了

Answer 1

this.cc=function() 
            { 
var obj = this;
                xmlhttp.onreadystatechange=function () 
                    { 
                        if(xmlhttp.readyState==4) 
                            { 
                                alert(obj.str);//注意这边弹出 这边弹出undefine 
                                document.getElementById(this.div_id).innerHTML=xmlhttp.responseText; 
                                document.getElementById("newDrag").style.display="block"; 
                            } 
                            
                            
                    } 
                xmlhttp.open('POST',this.url_str,true); 
                xmlhttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
                xmlhttp.send(this.str); 
                alert(this.str);//这里弹出正常 
            } 这样试试

Answer 2

因为此this非彼this也。呵呵。帮你改一下。怎么今天大家都对AJAX这么感兴趣呢
function ajax() 
    { 
        var xmlhttp=createXMLHttp(); 
        this.url_str='';//php后台文件 
        this.div_id='';//加载的图层id 
        this.str='';//传送的数据 
        var that = this;
        this.cc=function() 
            { 
                xmlhttp.onreadystatechange=function () 
                    { 
                        if(xmlhttp.readyState==4) 
                            { 
                                alert(that.str);//注意这边弹出 这边弹出undefine 
                                document.getElementById(this.div_id).innerHTML=xmlhttp.responseText; 
                                document.getElementById("newDrag").style.display="block"; 
                            } 
                            
                            
                    } 
                xmlhttp.open('POST',this.url_str,true); 
                xmlhttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
                xmlhttp.send(this.str); 
                alert(this.str);//这里弹出正常 
            } 
    } function character_ajax(user_id,type,mission_id) 
    { 
        var aa=new ajax(); 
        aa.url_str='character.php'; 
        aa.div_id="newBody"; 
        aa.str="user_id="+user_id+'&type='+type 
        aa.cc(); //弹出的是undefine 
    }