node.js - while循环代码在node js中没有顺序执行

Question

尝试在while循环中执行代码并设置标志，但无法设置标志，它带有初始标志值。我的代码如下:

var flag = 0
while(!flag)
{
    connection.query('SELECT nlc,id,user_id FROM tbl_buy WHERE `type`="buy" AND `status`="available" AND coin_id="'+jsondata.coinid+'" AND order_type="market" order by id ASC LIMIT '+offset+',1',function (error,results, fields)
    { 
        if(results.length > 0)
        {
            flag = 1; // want to set flag when i recieve the result 
            connection.query('SELECT tbl_buy.* from (select tbl_buy.*, (@sum := @sum + nlc) as cume_stock from tbl_buy cross join (select @sum := 0) params  WHERE tbl_buy.type="sell" AND tbl_buy.status="available" AND tbl_buy.user_id!="'+results[0].user_id+'" AND tbl_buy.coin_id="'+jsondata.coinid+'" AND tbl_buy.order_type="market" order by id ) tbl_buy where cume_stock-nlc < "'+results[0].nlc+'"',function (error,results_arr, fields)
            {
                res.end(JSON.stringify(results_arr));
                myCallback(results,results_arr);
            });
        }
    });
    console.log('flag value :  '+flag); // this line executes first and then the query is been executed , here the value remains same (ie flag = 0 and not changed to 1)
    offset++;
} 

不明白为什么控件转到 console.log('flag value : '+flag);而不是顺序执行

Answer 1

因为 Node 是异步的。这就是为什么当您的查询阻塞处理时，它将您的代码插入事件循环并在您的情况下执行下一条语句console.log('flag value : '+flag);