• • 此问题在此处已有答案**：

Check for isNewUser with Firebase email link auth using modular JS SDK（1个答案）
15小时前关门了。
在v8中，我是这样做的：

const userCredential = await firebase.auth().signInAnonymously();
console.log('is new user: ', userCredential.additionalUserInfo.isNewUser());

然而，在V9中：

const userCredential = await SignInWithPopup(auth, googleProvider);
try {
  userCredential.additionalUserInfo.isNewUser()
}
catch (e) {
  console.log(e);
  /* [!] TypeError: Cannot read properties of undefined (reading 'isNewUser') */
}

additionalUserInfo在signin函数返回的UserCredential对象上不存在，在V9中应该怎么做？