SignUp.tsx

// ...

type User = {
  id: string
  uuid: string
  name: string
  email: string
  createdAt: string
  updatedAt: string
  deletedAt: string
}

const SignUp: React.FC = () => {
	// ...

  const createUser = useCallback(
    async (params: { email: string | null; uuid: string }) => {
      return await api.post<User>(`${API_URL}/api/users`, params)
    },
    [],
  )

  const setAPIToToken = useCallback(
    async (fb: firebase.auth.UserCredential) => {
      const idToken = await fb.user?.getIdToken()
      if (!idToken) {
        console.warn('[Firebase error]: idToken is not provided')
        return
      }
      api.setToken(idToken)
    },
    [],
  )

  const handleSignUpWithGitHub = useCallback(async () => {
    const provider = new firebase.auth.GithubAuthProvider()

    try {
      const currentUser = await firebase.auth().currentUser

      const res = currentUser
        ? await currentUser.linkWithPopup(provider)
        : await firebase.auth().signInWithPopup(provider)

      await setAPIToToken(res)

      if (!currentUser) {
        const firebaseUser = res.user as firebase.User
        const user = await createUser({
          email: firebaseUser.email,
          uuid: firebaseUser.uid,
        })
        console.log('user: ', user)
      } else {
        // maybe get user through API
      }
    } catch (err) {
      // error handling
      console.error(err)
    }
  }, [createUser, setAPIToToken])

  const handleSubmit = useCallback(
    async (e: SyntheticEvent) => {
      e.preventDefault()

      const { email, password } = state

      try {
        const res = await firebase
          .auth()
          .createUserWithEmailAndPassword(email, password)

        await setAPIToToken(res)

        const firebaseUser = res.user as firebase.User
        const user = await createUser({
          email: firebaseUser.email,
          uuid: firebaseUser.uid,
        })
        console.log('user: ', user)
      } catch (e) {
        // error handling
        console.error(e)
      }
    },
    [createUser, setAPIToToken, state],
  )
				
	// ...			
}

export default SignUp