How to implement registration and login function in NodeJs+MySQL

//连接池
let db=mysql.createPool({'配置'})   
db.query(`sql语句`,(err,data)=>{})

function md5(str){
  let obj=crypto.createHash('md5');
  obj.update(str);
  return obj.digest('hex')
}
function md5_2(str){
  return md5(md5(str))
}

const http=require('http');
const fs=require('fs');
const mysql=require('mysql');
const url=require('url');
const zlib=require('zlib');
const crypto=require('crypto');
 
const _key='bsjhjqbj1;dqwxsxx+';
 
let server=http.createServer((req,res)=>{
  let {pathname,query}=url.parse(req.url,true);
  let {user,password}=query;
 
  switch(pathname){
    case '/reg':
      if(!user){
        res.write('{"err":1,"msg":"用户名不能为空"}');
        res.end();
      }else if(!password){
        res.write('{"err":1,"msg":"密码不能为空"}');
        res.end();
      }else if(!/\w{4,16}$/.test(user)){
        res.write('{"err":1,"msg":"用户名应为大小写字母数字或下划线"}');
        res.end();
      }else if(/['|"]/.test(password)){
        res.write('{"err":1,"msg":"密码非法"}');
        res.end();
      }else{
        db.query(`SELECT username FROM users_table WHERE username='${user}'`,(err,data)=>{
          if(err){
            res.write('{"err":1,"msg":"数据库错误"}');
            console.log(err)
            res.end()
          }else{
            if(data.length>0){
              res.write('{"err":1,"msg":"用户名已存在"}');
              res.end();
            }else{
              res.write('{"err":0,"msg":"注册成功"}');
              db.query(`INSERT INTO users_table (ID,username,password) VALUES (0,'${user}','${md5_2(password)}')`);
              res.end();
            }
          }
        })
      }
      break;
 
    case '/login':
      if(!user){
        res.write('{"err":1,"msg":"用户名不能为空"}');
        res.end();
      }else if(!password){
        res.write('{"err":1,"msg":"密码不能为空"}');
        res.end();
      }else if(!/\w{4,16}$/.test(user)){
        res.write('{"err":1,"msg":"用户名应为大小写字母数字或下划线"}');
        res.end()
      }else if(/["|']/.test(password)){
        res.write('{"err":1,"msg":"密码非法"}');
        res.end();
      }else{
        db.query(`SELECT username,password FROM users_table WHERE username='${user}'`,(err,data)=>{
          if(err){
            res.write('{"err":1,"msg":"数据库错误"}');
            res.end()
          }else if(data.length>0){
            if(md5_2(password)!=data[0].password){
              res.write('{"err":1,"msg":"用户名或密码不正确"}');
              res.end();
            }else{
              res.write('{"err":0,"msg":"登陆成功"}');
              res.end();
            }
          }else{
            res.write('{"err":1,"msg":"用户不存在"}')
          }
        })
      }
    break;
 
    default:
      let rs=fs.createReadStream(`www${pathname}`);
      let gz=zlib.createGzip();
 
      res.setHeader('content-encoding','gzip');
      rs.pipe(gz).pipe(res);
      rs.on('error',err=>{
        res.writeHeader(404);
        res.write('Not Found');
        res.end();
      });
  }
});
 
server.listen(8888);