Node.js 等待回调完成，然后在节点js中执行下一条语句

NodeJs的新成员。我在同步方法执行时遇到问题。这就是我的意思，我有一个控制器，负责： A.调用方法（在单独的JS文件中）打开数据库连接并检索数据。 B然后它将数据发送到前端。 从我的调试工作来看，我似乎是在打开连接并获取数据的方法完成之前发送数据的。我之所以知道这一点，是因为当执行salesController.js的最后一行时，它会给出错误“无法读取未定义的属性”Recordset”。在下面的代码段中，dbAccess.js具有打开数据库并获取数据的方法。然后salesController.js发送该数据。需要salesController.js中突出显示部分的帮助。请注意，如果有帮助，我将使用sql server作为后端

dbAccess.js

const dbConfig = require('../../nodeApp/dbConfig')

module.exports = {
    makeDBAccess: function(sqlString, req, res) {
        var sql = require("mssql/msnodesqlv8");
        // connect to your database
        sql.connect(dbConfig, function (err) {


            if (err) console.log(err);

            // create Request object
            var request = new sql.Request();

            // query to the database and get the records
            request.query(sqlString, function (err, recordset) {

                if (err) console.log(err)

                console.log(recordset.recordsets[0]);
                console.log(recordset.recordsets[0].length)

                return recordset;
            });
        });
    }
}

salesController.js

const express = require('express');
var router = express.Router();
var dbAccess = require('../utility/dbAccess.js')
var utility = require('../utility/readfile.js')


router.get('/totalSales2011', function (req, res) {
    var sqlString = utility.readFileFunc("queries/sales2011.sql");
    var recordSet = dbAccess.makeDBAccess(sqlString,req,res); **//Get data from database**
    res.send(recordSet.recordsets[0]); **//Wait for line above to complete before doing this.**
});

module.exports = router;

---

原因在javascript函数中返回

undefined

如果未添加

return

语句，则

makeDBAccess

函数不包含返回，因此它返回

undefined

至于怎么做，您需要使用or，因为连接到数据库和进行数据库查询都是异步操作

dbAccess.js

const dbConfig = require('../../nodeApp/dbConfig')

module.exports = {
    makeDBAccess: function(sqlString, callback) {
        var sql = require("mssql/msnodesqlv8");
        // connect to your database
        sql.connect(dbConfig, function (err) {


            if (err) return callback(err);

            // create Request object
            var request = new sql.Request();

            // query to the database and get the records
            request.query(sqlString, function (err, recordset) {

                if (err) return callback(err)


                return callback(null, recordset);
            });
        });
    }
}

const express = require('express');
var router = express.Router();
var dbAccess = require('../utility/dbAccess.js')
var utility = require('../utility/readfile.js')


router.get('/totalSales2011', function (req, res) {
    var sqlString = utility.readFileFunc("queries/sales2011.sql");
    var recordSet = dbAccess.makeDBAccess(sqlString, (err, recordSet) => {
          if (err) console.error(err);
          else res.send(recordSet.recordsets[0]);
    });

});

module.exports = router;

salesController.js

const dbConfig = require('../../nodeApp/dbConfig')

module.exports = {
    makeDBAccess: function(sqlString, callback) {
        var sql = require("mssql/msnodesqlv8");
        // connect to your database
        sql.connect(dbConfig, function (err) {


            if (err) return callback(err);

            // create Request object
            var request = new sql.Request();

            // query to the database and get the records
            request.query(sqlString, function (err, recordset) {

                if (err) return callback(err)


                return callback(null, recordset);
            });
        });
    }
}

const express = require('express');
var router = express.Router();
var dbAccess = require('../utility/dbAccess.js')
var utility = require('../utility/readfile.js')


router.get('/totalSales2011', function (req, res) {
    var sqlString = utility.readFileFunc("queries/sales2011.sql");
    var recordSet = dbAccess.makeDBAccess(sqlString, (err, recordSet) => {
          if (err) console.error(err);
          else res.send(recordSet.recordsets[0]);
    });

});

module.exports = router;