[Vuejs]-VueJS & Firebase – How to validate someone's password

Try to add async to your function:

 isPreviousPassword: async (v) => {
  var credentials = await firebase.auth().currentUser
    .reauthenticateWithCredential(
        firebase.auth.EmailAuthProvider.credential(
        firebase.auth().currentUser.email, 
        v)
    )

  return credentials || 'Your password is incorrect'
}