有一些中间件的变化在新版本的表达，我已经做了一些改变，在我的代码周围的一些其他职位对这个问题，但我不能得到任何坚持。请帮帮我。这是我的index.js文件

const express = require("express");
const app = express();
const dotenv = require("dotenv");
const mongoose = require("mongoose");
const router = express.Router();
dotenv.config("");

//connect to db
mongoose.connect(
    process.env.DB_CONNECT,
    { useUnifiedTopology: true, useNewUrlParser: true },
    ()=> console.log("connected to db")
);

//IMPORT ROUTES

const productRoutes = require("./routes/product");

//routes middlewars
app.use("./api/products", productRoutes);
 

app.listen(4000, () => console.log("server is running on port 4000!"));

module.exports = router ;

和投掷错误

TypeError: Router.use() requires a middleware function but got a Object
    at Function.use (C:\Users\HP\node-api\node_modules\express\lib\router\index.js:469:13)
    at Function.<anonymous> (C:\Users\HP\node-api\node_modules\express\lib\application.js:22
7:21)
    at Array.forEach (<anonymous>)
    at Function.use (C:\Users\HP\node-api\node_modules\express\lib\application.js:224:7)
    at Object.<anonymous> (C:\Users\HP\node-api\index.js:21:5)
    at Module._compile (node:internal/modules/cjs/loader:1159:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1213:10)
    at Module.load (node:internal/modules/cjs/loader:1037:32)
    at Module._load (node:internal/modules/cjs/loader:878:12)
    

Node.js v18.12.1
error is