javascript - Node.js 返回的不是一个函数

Question

我想使用登录方法，但是当我定义和导入时，浏览器返回的不是函数

{code: -1, msg: "登录不是函数", error: 500, errorMsg: "登录不是函数"}

我是一个初学者，我的一般逻辑是从第一段代码开始调用登录。登录写在第二段代码中，然后第二段会调用第三段SQL的函数

    const express = require('express')
    const Result=require('../models/Result')
    const login=require('../services/user')
    // const debug = require('../utils/constant').debug
    const router = express.Router()

    router.post('/login', function(req, res) {
      console.log('/user/login', req.body)
      // debug && console.log(sql);
      const {username,password}=req.body
      login(username,password).then(user=>{
        if(!user||user.length ===0){
          new Result('登陆成功').success(res)
        }else{
          new Result('登陆失败').fail(res)
        }
      })

    })
    module.exports = router

./services/user

const {querySql}=require('../db')
return function login(username,password){
    querySql("select * from admin_user where username='${username}' and password='${password}'").then(results =>{
    }).catch(err =>{
      console.log(err);   
    })
}
module.exports={

}

和./db/index.js

const mysql =require('mysql')
const config =require('./config')
function connect() {
    return mysql.createConnection({
      host:config.host,
      user:config.user,
      password:config.password,
      database:config.database,
      multipleStatements: true
    })
  }

function querySql(sql){
  const conn =connect()
  return new Promise((resolve,reject)=>{
    try{
      conn.query(sql,(err,results) => {
        if(err){
          reject(err)
        }else{
          resolve(results)
        }
      })
    }catch(e){
      reject(e)
    }finally{
      conn.end()
    }
  })
}
module.exports={
  connect,
  querySql
}

新错误

  querySql("select * from admin_user'")
  ^

TypeError: querySql is not a function
    at login (/Users/dujinyang/admin-imooc-node/services/user.js:3:3)
    at Object.<anonymous> (/Users/dujinyang/admin-imooc-node/services/user.js:7:17)

和新的querySql

const mysql =require('mysql')
const config =require('./config')
function connect() {
    return mysql.createConnection({
      host:config.host,
      user:config.user,
      password:config.password,
      database:config.database,
      multipleStatements: true
    })
  }

function querySql(sql){
  const conn =connect()
  return new Promise((resolve,reject)=>{
    try{
      conn.query(sql,(err,results) => {
        if(err){
          reject(err)
        }else{
          resolve(results)
        }
      })
    }catch(e){
      reject(e)
    }finally{
      conn.end()
    }
  })
}
exports.querySql = querySql();

Answer 1

NodeJS 中的函数是导出的，而不是返回的。

function login(username,password){
     querySql(`select * from admin_user where username=${username} and password=${password}`)
          .then(results =>{})
          .catch(err =>{ console.log(err); })
 }

exports.login = login();

然后

const {login} = require('../services/user');