W3School socket.io官方文档案例纠正

引用socket.io.js未在服务端设置静态文件，导致客户端报错socket.io.js notfound

问题地址:https://www.w3cschool.cn/socket/socket-ulbj2eii.html
问题代码：

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

app.get('/', function(req, res){
  res.sendFile(__dirname + '/index.html');
});

io.on('connection', function(socket){
  console.log('a user connected');
});

http.listen(3000, function(){
  console.log('listening on *:3000');
});

正确代码：

var express = require('express');
var app = express();
var http = require('http').Server(app);
var io = require('socket.io')(http);
app.use(express.static('socket.io'));
app.get('/', function(req, res){
  res.sendFile(__dirname + '/index.html');
});

io.on('connection', function(socket){
  console.log('a user connected');
});

http.listen(3001, function(){
  console.log('listening on *:3000');
});