Javascript Firebase函数承诺未定义类型错误

我目前正在使用firebase函数从数据库调用以下文档：

let token, userId;
db.doc(`/users/${newAccount.username}`)
    .get()
    .then((doc) => {
        if (doc.exists === false) {
            return firebase.auth().createUserWithEmailAndPassword(newAccount.email, newAccount.password).catch(err => console.error(err));
        } else {
            res.status(400).json({ username: 'this username is already taken' });
        }

    })

    .then(data => {
        userId = data.user.uid;
        return data.user.getIdToken();
    })

    .then((idToken) => {
        token = idToken;
        const userCredentials = {
            username: newAccount.username,
            email: newAccount.email,
            created: new Date().toISOString(),
            userId
        };
        return db.doc(`/users/${newAccount.username}`).set(userCredentials);

    })

    .then(() => {
        return res.status(201).json({ token });
    })
    .catch((err) => {
        console.error(err);
        if (err.code === 'auth/email-already-in-use') {
            return res.status(400).json({ email: 'Email is already is use' });
        } else {
            return res.status(500).json({ general: 'Something went wrong, please try again' });
        }
    });

TypeError: Cannot read property 'user' of undefined

代码运行正常，但如果数据库中存在文档，则会记录错误：

let token, userId;
db.doc(`/users/${newAccount.username}`)
    .get()
    .then((doc) => {
        if (doc.exists === false) {
            return firebase.auth().createUserWithEmailAndPassword(newAccount.email, newAccount.password).catch(err => console.error(err));
        } else {
            res.status(400).json({ username: 'this username is already taken' });
        }

    })

    .then(data => {
        userId = data.user.uid;
        return data.user.getIdToken();
    })

    .then((idToken) => {
        token = idToken;
        const userCredentials = {
            username: newAccount.username,
            email: newAccount.email,
            created: new Date().toISOString(),
            userId
        };
        return db.doc(`/users/${newAccount.username}`).set(userCredentials);

    })

    .then(() => {
        return res.status(201).json({ token });
    })
    .catch((err) => {
        console.error(err);
        if (err.code === 'auth/email-already-in-use') {
            return res.status(400).json({ email: 'Email is already is use' });
        } else {
            return res.status(500).json({ general: 'Something went wrong, please try again' });
        }
    });

TypeError: Cannot read property 'user' of undefined

我想这个承诺还在履行，我有点纠结于如何结束它

---

任何帮助都将不胜感激。谢谢。

您的第二个

回调将在所有情况下被调用。在第一次回调中发送400响应实际上不会阻止承诺传播到以下所有
然后
回调

如果要停止
然后执行
回调链，则应该抛出一个错误，由链下的
catch
捕获，跳过所有
然后