jquery用Ajax中的回调函数时注意事项

<script language="javascript" type="text/javascript" src="<?php echo base_url();?>/js/jquery-1.7.2.min.js"></script>
<script>
function add_ip(bip,eip,area_id) {
        var action = "<?php echo site_url(‘test/add_test‘); ?>";
        var yn = window.confirm("测试");
        if (!yn) {
                return;
        }
        $.ajax({
                type:"post",
                dataType:"json",
                url:action + "?rr=" + Math.random(),
                data:{
                "bip": bip,
                "eip": eip,
                "area": area_id
                },
                success:function(retObj) {
                        if (retObj.code == 0) {
                                alert("设置成功");
                        } else {
                                alert("设置失败:"+retObj.msg);
                        }
                },
                fail:function(retObj) {
                        alert("发送请求失败code="+retObj.code);
                }
        });
}

</script>

function add_test() {
                $bip = $this->input->post(‘bip‘, true);
                $eip = $this->input->post(‘eip‘, true);
                $area_id = intval($this->input->post(‘area_id‘,true));
                if ($this->test_mdl->add($bip, $eip, $area_id)) {
                //      echo "add OK";  
                } else {
                //      echo "add fail";
                }       
                echo ‘{"code":0, "msg":""}‘;
        }