Express路由报错：Cannot read property 'caseSensitive' of undefined 求助

错误信息 #

TypeError: Cannot read property 'caseSensitive' of undefined
at route (D:\node_js\myownapi\node_modules\express\lib\router\index.js:506:21)
at Layer.handle [as handle_request] (D:\node_js\myownapi\node_modules\express\lib\router\layer.js:95:5)
at trim_prefix (D:\node_js\myownapi\node_modules\express\lib\router\index.js:328:13)
at D:\node_js\myownapi\node_modules\express\lib\router\index.js:286:9
at Function.process_params (D:\node_js\myownapi\node_modules\express\lib\router\index.js:346:12)
at next (D:\node_js\myownapi\node_modules\express\lib\router\index.js:280:10)
at urlencodedParser (D:\node_js\myownapi\node_modules\body-parser\lib\types\urlencoded.js:91:7)
at Layer.handle [as handle_request] (D:\node_js\myownapi\node_modules\express\lib\router\layer.js:95:5)
at trim_prefix (D:\node_js\myownapi\node_modules\express\lib\router\index.js:328:13)
at D:\node_js\myownapi\node_modules\express\lib\router\index.js:286:9

问题代码 #

app.js #

const express = require('express')
const app = express()
const {route} = require('./routes/route')
app.use(express.static('./public'));
app.use(express.json());
app.use(express.urlencoded());
app.use(route)
app.listen(5000,()=>{
console.log('server is listening at port 5000...')
})

route.js #

const { items } = require("../data");
const express = require("express");
const route = express.Router();
route.get("/", (req, res) => {
  res
    .send('<h1>Home Page</h1><a href="/api/v1/items">products</a>')
    .status(200);
});
route.get("/api/v1/items", (req, res) => {
  const newItems = items.map((item) => {
    const { id, name, img, price, desc, category } = item;
    return { id, name, img, price, desc, category };
  });
  res.json(newItems);
});
route.get("/login.html", (req, res) => {
  res.sendFile(__dirname + "/public/sigup.html");
});

route.post("/", (req, res) => {
  console.log(req.body.emailid);
  if (req.body.emailid === "abc@gmail.com") {
    res.status(200).redirect("signup.html");
    console.log(req.body.emailid);
  } else {
    route.get("/errormsg", (req, res) => {
      const msg = "please Enter valid Email id";
      res.status(401).json({ msg });
    });
  }
});
module.exports = route;

问题原因 #

1. 导入方式错误：app.js里用了解构赋值const {route} = require('./routes/route')，但route.js是默认导出module.exports = route，解构会得到undefined。把undefined传给app.use()，Express内部处理路由时找不到预期的router对象，就会抛出Cannot read property 'caseSensitive' of undefined错误。
2. 动态添加路由的错误操作：route.js的POST请求处理函数里，else分支动态调用route.get("/errormsg", ...)，这不符合Express的路由定义规范——路由应该在应用启动前一次性定义完成，动态添加会导致路由栈异常，也可能触发类似错误。

修复方案 #

1. 修正app.js的导入方式 #

把解构导入改成默认导入：

// app.js里的导入语句替换成
const route = require('./routes/route')

2. 修正POST请求的错误处理逻辑 #

删除动态添加路由的代码，直接在else分支里返回错误响应，不需要新增路由：

route.post("/", (req, res) => {
  console.log(req.body.emailid);
  if (req.body.emailid === "abc@gmail.com") {
    res.status(200).redirect("signup.html");
    console.log(req.body.emailid);
  } else {
    // 直接返回错误，不要动态加路由
    const msg = "please Enter valid Email id";
    res.status(401).json({ msg });
  }
});

另外补充两个小问题：

• route.js里的res.sendFile(__dirname + "/public/sigup.html")，文件名拼写错误（sigup应该是signup），建议修正。
• express.urlencoded()最好加上{extended: true}参数，避免后续解析表单数据时出现问题：app.use(express.urlencoded({extended: true}));

内容的提问来源于stack exchange，提问作者Divili Srikanth