No 'Access-Control-Allow-Origin' header is present on the requested resource. How to fix the situation?

Question

JavaScript

I use Ionic, Socket.io in the project. The backend is written in node.js.
I'm trying to reach a server located in the Cloud9 cloud using the client.
Gives an error:
XMLHttpRequest cannot load https:/URL. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin ' 192.168.10.159:8100 ' is therefore not allowed access.
As I understand it, the problem is security, that Chrome does not allow access to an external resource.
Tried:
1) "C:\Program Files (x86)\Google\Chrome\Application\chrome.exe" --allow-file-access-from-files --disable-web-security
2) ionic project
"proxies": {
"path": "/chat",
"proxyUrl": "
}
3) I tried a plugin that disables/enables CORS for Chrome.
Everywhere is the same. Does not help
I contact the server through the service:

angular.module('starter')

.factory('Socket', function (socketFactory) {
  var url = 'https:...';  
  var myIoSocket = io.connect( url );

  mySocket = socketFactory({
    ioSocket: myIoSocket
  });

  return mySocket;
});

On server:

// Including Express.js
var express = require('express');
// Creating app Express
var app = express();

// Creating server using express and http
var server = require('http').createServer(app);

How to cure this ailment, since going further is not an option ...?
PS Changed the server

var express = require('express');
var app = express();
var http = require('http');
var server = http.createServer(app);

server.on('request', function(req, res) {
res.writeHead(200, {
'Content-Type': 'text/event-stream; charset=utf-8',
'Cache-Control': 'no-cache',
'Access-Control-Allow-Origin': '*'
});

res.end();
})

In this case, I have another error: XMLHttpRequest cannot load https://URL. A wildcard '*' cannot be used in the 'Access-Control-Allow-Origin' header when the credentials flag is true. Origin '192.168.10.159:8100' is therefore not allowed access. The credentials mode of an XMLHttpRequest is controlled by the withCredentials attribute.
How to deal with it?

Answer 1

I recently tested the EventSource and accessed cloud9 through angular2. Had the same problem.
I solved by setting Access-Control-Allow-Origin on the server via

res.writeHead(200, {
  'Access-Control-Allow-Origin': '*',
  // 'Access-Control-Allow-Credentials': true 
});

Another option if express is used

var express = require('express'), 
  cors = require('cors'), 
  app = express();

app.use(cors());
// или
app.use(cors({
    origin: true,
    credentials: true
}));

Answer 2

1) ionic proxy should work
2) Chrome launched with the flag should work (but it needs to be launched from scratch - if Chrome is already open, it will just pop into the foreground, without applying the flag, of course)

Answer 3

Make the server issue this parameter in the header. I had the same crap.