sio-test.js

const fs = require("fs");
const http = require("http");
const https = require("https");
const { Server } = require("socket.io");
const express = require("express");

//defaults
const tlsEnabled = true;
const port = 3000;

const app = express();

let server;
if (tlsEnabled) {
	const key = fs.readFileSync("key.pem");
	const cert = fs.readFileSync("cert.pem");

	const options = {
		key,
		cert,
	};

	server = https.createServer(options, app);
} else {
	server = http.createServer(app);
}

const io = new Server(server);

server.listen(port, () => {
	if(tlsEnabled)
	{
		console.log("SSL Server open on localhost:" + port);
	}
	else{
		console.log("Server open on localhost:" + port);
	}
});

io.on("connection", (socket) => {
	console.log(socket.id + " connected.");
	socket.on("disconnect", (reason) => {
		console.log(socket.id + " disconnected: " + reason);
	});
});

Forked for minor modifications and log verbosity. Resolve/Reject did not work on my end.

Comment copied from upstream:
Reference documentation: https://nodejs.org/en/knowledge/HTTP/servers/how-to-create-a-HTTPS-server/

To generate a self-signed certificate:

openssl genrsa -out key.pem
openssl req -new -key key.pem -out csr.pem
openssl x509 -req -days 9999 -in csr.pem -signkey key.pem -out cert.pem
rm csr.pem