Question

我在fun1中有两个函数fun1（）和fun2（），调用fun2，返回状态，其中其余代码在fun1中工作但在fun2之前返回fun1其余代码已执行！因为节点js是一个基于Unblocked程序代码的程序！如何处理我的案子？

    async function isDuplicateUser(emailId)
{
  var condition=false;
  var con = mysql.createConnection({
    host:"localhost",
    user: "root",
    password: "32577488",
    database:"mydb"
  });
  var sql='SELECT count(*) AS namesCount FROM UserDetails WHERE emailId ="'+emailId+'";';
  con.connect(function(err) {
    con.query(sql, function (err, result) {
      if (err){
        throw err;
        return ;
      }
      if(result[0].namesCount>=1)
      {
        condition=true;
        console.log("Upper check :"+condition);
      }
    });
  });
  console.log("Lower check :"+condition);
  return condition;
}

在记录器中，我首先看到LowerCheck，然后上检查记录器请帮助我！

Answer 1

您可以使用以下方法解决此问题：

回调（仅限纯ES5解决方案）
承诺（我的解决方案）
异步函数（也使用Promises）

因为Promise对我来说是最直观的，所以我在ES6和Promises中编写了工作解决方案：

＆＃13;

const express = require('express');
const bodyParser = require('body-parser');
const app = express();
const mysql = require('mysql');

const connectionConfig = {
  host:"localhost",
  user: "root",
  password: "",
  database:"mydb"
}

/** Firstly, connect with DB; so you will be able to share connection */
const conn = mysql.createConnection(connectionConfig);
conn.connect((err) => {
  if (err) throw err;

  /** After then create server */
  app.use(bodyParser.urlencoded({ extended: true }));
  app.use(bodyParser.json());

  app.get('/',(req,res) => { res.send(`hello express`) });
  app.get('/about',(req,res) => { res.send(`Thank you!`) });

  app.post('/signup', (req, res) => {

    isDuplicateUser(req.body.email)
      .then((userPresent) => {

        if(userPresent) {
          console.log(`User Already present`);
          res.status(409).json({message: `User already present`});
        } else {
          const query = `INSERT INTO UserDetails (email, password, name) VALUES ('${req.body.email}', '${req.body.password}','${req.body.name}')`;
          conn.query(query, function (err, result) {
            if (err) throw err;
            console.log(`1 record inserted`);
            res.status(200).json({message: `1 record inserted`});
          });
        }

      })
      .catch((err) => {
        console.log(`An unexpected error occurred`);
        res.status(500).json({message: `An unexpected error occurred`});
      });

  });

  app.listen(8080, () => console.log('Server running at http://127.0.0.1:8080/') );

  function isDuplicateUser(email) {
    return new Promise((resolve, reject) => {
      const query = `SELECT count(*) AS namesCount FROM UserDetails WHERE email='${email}';`;
      conn.query(query, (err, result) => {
        if (err) reject(err);
        resolve(result[0].namesCount > 0 ? true : false);
      });
    })
  }

});

＆＃13;

请注意，我在DB中重命名了列的名称。

我希望，这个例子可以帮助您了解如何使用异步代码。

如何调用函数调用首先发生

1 个答案: