Express报错TypeError: Router.use()需中间件函数却得到对象，求解决

你的index.js代码运行后抛出了上述错误，先看你的代码和错误信息：

你的index.js代码 #

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 ;

报错信息 #

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:227:21)
    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

错误原因及修复方法 #

1. 路由路径前缀格式错误 #

app.use的第一个参数是路径前缀，必须以/开头，你写的./api/products是相对路径格式，Express无法识别，会导致后续解析错误。改成/api/products即可。

2. 多余的Router实例定义 #

你在index.js里声明了const router = express.Router();但完全没用到，最后还导出了这个空Router，属于冗余代码，直接删掉这两行（const router = express.Router();和module.exports = router ;）。

3. 确保productRoutes正确导出Express Router #

检查你的./routes/product.js文件，必须正确创建并导出Router实例，示例代码如下：

const express = require("express");
const router = express.Router();

// 示例路由
router.get("/", (req, res) => {
  res.send("Products list");
});

module.exports = router;

修复后的index.js代码 #

const express = require("express");
const app = express();
const dotenv = require("dotenv");
const mongoose = require("mongoose");

dotenv.config(); // 无需传空字符串，dotenv会自动加载根目录的.env文件

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

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

内容的提问来源于stack exchange，提问作者Sheetal Dwivedi