socket.io after build package

[zhangwuyang-github]

Server.js:
const express = require('express')
const app = express()
const socket = require('socket.io')
const color = require('colors')
const cors = require('cors')
const { get_current_user, user_disconnect, join_user } = require('./dummyuser')

app.use(express())

const PORT = 80

app.use(cors())

let server = app.listen(
PORT, () => {
console.log(Server is Listening on PORT: ${PORT}.green)
}
)

io.set('origins', ':')

io.on('connection', socket => {
socket.on('joinRoom', ({ username, roomname }) => {
const p_user = join_user(socket.id, username, roomname)
console.log(socket.id, '=id')
socket.join(p_user.room)

    socket.emit('message', {
        userId: p_user.id,
        username: p_user.username,
        text: `欢迎来到聊天室, ${p_user.username}`..........: 

打包后报错：

�npm start is correct, but after npm run build, the wrong comes.