async handleSubmit(event) {
  event.preventDefault()
  const { username, password } = this.state

  try {
    const response = await fetch('/log_in', {
      method: 'post',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ username, password })
    })
  }

 catch (error) {
    console.log(error)
  }
}

app.post('/log_in', (req,res) => {
    console.log(`login form data`);
    console.log(`Username : ${req.body.username}`);
    console.log(`password : ${req.body.password}`);
    if(req.body.username == "user" && req.body.password == "123"){
        res.redirect('/')
    }
})