jquery 中ajax的所有状态

<script src='jquery.js'></script>  
<script>  
$(function(){  
        $("#starts").click(function(){  
            $.ajax({  
                type:'POST',  
                url:'ajax.test.php',  
                data:"username=2",  
                dataType:'text',  
                cache:false,  
                beforeSend: function(XMLHttpRequest){  
                    $("#loading").show();  
                },  
                success:function(msg){  
                    alert(msg);  
                },  
                complete: function(XMLHttpRequest, textStatus){  
                    $("#loading").hide();  
                },  
                error:function(data){  
                     if(data.status=="404"){  
                        alert('请求地址出错！');  
                    }  
                    else if(data.status=="302"){  
                        alert('连接网页出错');  
                    } else if(data.status=="timeout"){  
                        alert("请求超时!");  
                    }else{  
                        alert('请求未响应!请检查网络或VPN连接');  
                    }  
                }  
            });  
        });  
});  
</script>  
<span id="starts" style="cursor: pointer;">start</span>|||||||||||||  
<span id="loading" style="display:none;">loading......</span>