Node.js CORS问题（Nodejs+；Angular 6+；socket.io）

在Angular 6中，当我们尝试连接到服务器时，我们使用socket.io客户端面临CORS问题

浏览器控制台中出现的错误

Access to XMLHttpRequest at 'http://********.com/socket.io/?EIO=3&transport=polling&t=N3jTiAZ' from origin 'http://localhost:4200' has been blocked by CORS policy: 

The value of the 'Access-Control-Allow-Origin' header in the response must not be the wildcard '*' when the request's credentials mode is 'include'.

 The credentials mode of requests initiated by the XMLHttpRequest is controlled by the withCredentials attribute.

这是服务器代码

const express = require('express');
const bodyParser = require('body-parser');
const app = express();
const server = require('http').createServer(app);
const conn = app.listen("3000")
const io = require('socket.io').listen(conn);

io.origins('*:*') 

var connectioncheck = io.of('/check-connection');
connectioncheck.on('connection', function (socket) {
   console.log('user  connected');
});

下面是使用简单html和js的前端代码

   <script src="https://cdn.jsdelivr.net/npm/socket.io-client@2/dist/socket.io.js"></script>
var socket = io.connect('http://********.com/check-connection');
socket.emit('connection', "hello",function(db){
        console.log(db);
        console.log("data from callback");
    });

var socket=io.connect（'http://*********.com/check connection'）；
emit（'connection'，'hello'，函数（db）{
控制台日志（db）；
log（“来自回调的数据”）；
});

根据您在上面给出的评论，我认为您应该以如下方式使用NPM CORS

---

你试过npm使用cors吗？是的，我尝试了，但没有成功访问位于“http://******.com/socket.io/？EIO=3&transport=polling&t=N3jY9aF”“from origin”“的XMLHttpRequest已被CORS策略阻止：“Access Control Allow origin”标头包含多个值“*，”，但只允许一个值。当我尝试CORS时，我明白了这一点。我认为你应该以这里所述的方式使用NPM CORS。我尝试了它，但没有使用任何其他解决方案

let allowedOrigins = ["http://ServerA:3000", "http://ServerB:3000"]
let origin = req.headers.origin;
if (allowedOrigins.includes(origin)) {
  res.header("Access-Control-Allow-Origin", origin); // restrict it to the required domain
}