Node.js TS[2339]：类型 '() => Promise<(Document & Omit) ｜ 上不存在属性空>'

我已经使用以下内容定义了用户模式:

import mongoose from 'mongoose'
import { Model, Schema } from 'mongoose'
import bcrypt from 'bcrypt'

enum LoginType {
  EMAIL = 'email',
  GOOGLE = 'google',
}

interface IUser extends mongoose.Document {
  username: string
  email: string
  password: string
  loginTypes: LoginType
  comparePassword(password: string, callback: Function): Promise<Function>
}

interface IUserMethods extends Model<IUser> {
  comparePassword(password: string, callback: Function): Promise<Function>
}

type UserModel = Model<IUser, {}, IUserMethods>;

const userSchema = new Schema<IUser, UserModel, IUserMethods>({
  username: {
    type: String,
    required: true,
  },
  email: {
    type: String,
    required: true,
  },
  password: {
    type: String,
    require: true,
  },
  loginTypes: {
    type: String,
    require: true,
    enum: Object.values(LoginType),
  },
})

/* callback = (err: Error, isMatch: any) => {} */
userSchema.methods.comparePassword = async function (
  password: string,
  callback: Function
): Promise<Function> {
  let result
  try {
    result = await bcrypt.compare(password, this.password)
    return callback(null, result)
  } catch (err) {
    return callback(err, result)
  }
}

export default mongoose.model<IUser>('User', userSchema)

并在登录路径中调用它，但TypeScrip在foundUser.comparePassword(req.body.password, (err: Error, isMatch: any) => {})上显示错误Property 'comparePassword' does not exist on type '() => Promise<(Document<unknown, {}, IUser> & Omit<IUser & { _id: ObjectId; }, never>) | null>'.

以下是我的登录路由:

router.post('/credentials', (req, res) => {
  /* Check if user exists in database */
  const foundUser = async () => await User.findOne({ email: req.body.email })

  if (!foundUser) {
    res.status(401).send({ message: 'User does not exist' })
  }

  /* Check if password matches */
  foundUser.comparePassword(req.body.password, (err: Error, isMatch: any) => {})

  const jwt_token = jwt.sign(
    { name: req.body.name, email: req.body.email, id: req.body.id },
    JWT_SECRET,
    { expiresIn: '10000' }
  )
  res.status(200).send({
    name: req.body.name,
    email: req.body.email,
    id: req.body.id,
    jwt_token: jwt_token,
  })
})

I've search for it and try this solution before but not working.
While, I found

const a = new User({})
a.comparePassword(req.body.password, (err: Error, isMatch: any) => {})

就像mongoose doctor 说的那样，我可以正常工作，但如果我先用findOne再拨打comparePassword，那就不行了