Use of expressjs routing-level middleware

  node.js, question
var express=require("express");
 var app=express();
 var router = express.Router();
 
 router.use("/",function (req, res, next) {
 console.log("/");
 next();
 });
 router.use('/user', function (req, res) {
 console.log("/user");
 });
 app.use("/user",router);
 app.listen(3000);

I have just learned express, would you like me to enter app.use(“/user”,router) here? Why does the console output “/”instead of “/user”? Thank you

Res.send calledServerResponse.prototype.end(I think I remember correctly), so this http was closed when it was finished. The followingres.send("2")Implemented but will not return again.