Node JS maintains a long connection

const mysql = require('mysql');
const connect = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  password: 'root',
  database: 'blog'
});
connect.connect();
function keepalive (connect) {
  connect.query('select 1', [], function (err, result) {
    if (err) return console.log(err);
    // Successul keepalive
  });
}
//5 Send every hour  1 Hours  60 * 60 
setInterval(() => { keepalive(connect) }, 60 * 60 * 5);
module.exports = connect;

Cannot enqueue Handshake after invoking quit

node:events:505 

let mysql = require('../../config/db.js');


// Check whether this password has been registered 
  var sql = `select id,username from blog_admin where username = '${username}'`;
  console.log(sql);
  mysql.query(sql, function (err, result) {
    if (err) {
      console.log('[SELECT ERROR] - ', err.message);
      return;
    }
    if (result.length > 0) {
      res.send("<script>alert(' The user name already exists ！！');history.go(-1);</script>");
      return;
    }
    var md5 = crypto.createHash('md5');
    password = md5.update(password).digest('hex');
    var time = Math.round(((new Date()).getTime()) / 1000);
    var sql = `insert into blog_admin(username,password,status,time) values('${username}','${password}',${status},${time})`;
    mysql.query(sql, function (err, result) {
      if (err) {
        console.log('[SELECT ERROR] - ', err.message);
        return;
      }
      if (result.affectedRows == 1) {
        res.send("<script>alert(' Add success ');location.href='/admin/admin/add';</script>");
      } else {
        res.send("<script>alert(' Add failure ');history.go(-1);</script>");
      }
      console.log(result);
      //res.send("<script>alert(' Administrator added successfully ！！');</script>");
    })
  })