调用服务器时找不到socket.io

我正在尝试连接angular和nodejs服务器上的socket.io 在角度上,我已经声明了一个新的插座并连接它

import * as io from 'socket.io-client';
...
@component
...
const socket = io.connect('http://localhost:3000');

后端:server.js

const express = require('express');
const app = express();
var http = require('http').Server(app);
var io = require('socket.io')(http);
io.set('origins', 'http://localhost:4200');

var routes = require('./routes/routes')(io);

app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(function (req, res, next) {
    res.header("Access-Control-Allow-Origin", "http://localhost:4200");
    res.header("Access-Control-Allow-Methods", "GET, POST, PUT ,DELETE");
    res.header('Access-Control-Allow-Credentials', true);

    res.header(
        "Access-Control-Allow-Headers",
        "Origin, X-Requested-With, Content-Type, Accept"
    );
    next();
});
io.on('connection', function (socket) {
    socket.emit('news', { hello: 'world' });
    console.log("connectd");
});
app.use('/', routes);
var server = app.listen(3000, function (io) {
})

应用程序正在编译并从服务器获取数据。但只有socket.io不工作 我得到这个错误:

得到 http://localhost:3000/socket.io/?EIO=3&transport=polling&t=MEpN9Qy 404(未找到)