var msg = ""$.ajax({            type:"POST",            url :"ajax/checkArray.php",            data:"nns_config_item_value="+nns_config_item_value,            success:function(data){                         if(data!==''){                            msg = data;                         }                }         });if(msg){   alert(msg);   return false;}else{   return true;}

上面一段代码，运行发现：msg始终是空。

我们需要在ajax中添加async : false,将ajax异步请求关闭。（默认是异步请求）

$.ajax({            type:"POST",            url :"ajax/checkArray.php",            data:"nns_config_item_value="+nns_config_item_value,            async : false,            success:function(data){                         if(data!==''){                            msg = data;                         }                }         });