问MissingPasswordError:未提供密码

EN

MissingPasswordError: No password given

<input type="password" class="input--text" name="password" id="password">

const btnSignup = document.querySelector('.btn').addEventListener('click', function () {
    let username = document.querySelector('#username').value;
    let password = document.querySelector('#password').value;
    let bday = document.querySelector('#bday').value;

    fetch('http://localhost:3000/users/signup', {
        method: "post",
        headers: {
            'Content-Type': 'application/json'
        },
        body: JSON.stringify({
            'username': username,
            'password': password,
            'bday': bday
        })
    }).then(response => {
        return response.json();
    }).then(json => {
        if (json.status === 'success') {
            let feedback = document.querySelector('.alert');
            feedback.textContent = "Sign up successful!";
            feedback.classList.remove('hidden');
        }
    })
})

const signup = async (req, res, next) => {
    const username = req.body.username;
    const password = req.body.password;
    const bday = req.body.bday;

    const user = new Users({
        username: username
    });
    /*user.bday = bday;*/
    await user.setPassword(password);
    await user.save()
        .then(result => {
            console.log(result.id);

            let token = jwt.sign({
                id: result._id
            }, "{this is a secret}");

            res.json({
                'status': 'success',
                'data': {
                    'token': token
                }
            })
        }).catch(error => {
            res.json({
                'status': 'error'
            })
        });
}