我试图在我正在构建的应用程序中散列密码，当我通过调用此函数（coffeesctipt）创建用户时，它们散列得很好：

UserSchema.pre 'save', (next) ->
  user = this
  hashPass(user, next)

hashPass = (user, next) ->
  # only hash the password if it has been modified (or is new)
  if !user.isModified('password')
    return next()
  # generate a salt
  bcrypt.genSalt SALT_WORK_FACTOR, (err, salt) ->
    if err
      return next(err)
    # hash the password using our new salt
    bcrypt.hash user.password, salt, (err, hash) ->
      if err
        return next(err)
      # override the cleartext password with the hashed one
      user.password = hash
      next()
      return
    return

但当我做一个更新，并有这个前：

UserSchema.pre 'findOneAndUpdate', (next) ->
  user = this
  hashPass(user, next)

我得到TypeError: user.isModified is not a function，如果我控制台日志用户在pre保存pre日志用户我更新，findandupdate pre不，id有办法访问文档在pre或我需要这样做的另一种方式？