Here how we can enable https server for Express Node Server

https-for-express-node-server.js

const express = require('express');
var bodyParser = require('body-parser')
const mongoose = require('mongoose');
const routes = require('./routes/routes');

// for HTTP and HTTPS listening
var fs = require('fs');
var http = require('http');
var https = require('https');
var privateKey  = fs.readFileSync('{PATH TO PRIVATE KEY}/privkey.pem', 'utf8');
var certificate = fs.readFileSync('{PATH TO CERTIFICATE}/fullchain.pem', 'utf8');
var credentials = {key: privateKey, cert: certificate};

// ...
// Your other app settings 
app.use(cors())
app.use(bodyParser.urlencoded({extended: true}))
app.use(bodyParser.json());
// app.use(express.json());
app.use(express.static('public'));
app.use('/', routes);

// ...


var httpsServer = https.createServer(credentials, app);

httpsServer.listen(8000);