updated server.js file and added comments throughout

server.js

@@ -1,22 +1,22 @@
-const path = require('path'); // for file paths
-const express = require('express'); // for server
-const session = require('express-session'); // for sessions
-const exphbs = require('express-handlebars'); // for handlebars
-const methodOverride = require('method-override'); // for handling PUT requests
-// Initializes Sequelize with session store
-const SequelizeStore = require('connect-session-sequelize')(session.Store); // for storing sessions in db store (sequelize) instead of memory store (cookie)
+const path = require('path'); // for file paths (https://nodejs.org/api/path.html) 
+const express = require('express'); // for server (https://expressjs.com/en/4x/api.html#app) or client (https://expressjs.com/en/4x/api.html#app)
+const session = require('express-session'); // for sessions (https://expressjs.com/en/resources/middleware/session.html)
+const exphbs = require('express-handlebars'); // for handlebars (https://expressjs.com/en/guide/using-template-engines.html) 
+const methodOverride = require('method-override'); // for handling PUT requests (method-override) (https://expressjs.com/en/resources/middleware/method-override.html) 
+// Initializes Sequelize with session store (https://expressjs.com/en/guide/behind-proxies.html) 
+const SequelizeStore = require('connect-session-sequelize')(session.Store); // for storing sessions in db store (sequelize) instead of memory store (cookie) (https://expressjs.com/en/guide/behind-proxies.html)
 
-const app = express(); // initializes express
-const PORT = process.env.PORT || 3001; // sets port to 3001 if not set in environment
+const app = express(); // initializes express (https://expressjs.com/en/4x/api.html#app) or express server (https://expressjs.com/en/4x/api.html#app) or express client (https://expressjs.com/en/4x/api.html#app)
+const PORT = process.env.PORT || 3001; // sets port to 3001 if not set in environment variables (default is 3001) 
 
 const routes = require('./controllers'); // routes for server and client side files (default is ./controllers/index.js) 
 const sequelize = require('./config/connection');  // for connecting to db with sequelize (default is ./config/connection.js) 
 
-app.use(methodOverride('_method')); // for handling PUT requests (method-override) 
+app.use(methodOverride('_method')); // for handling PUT requests (method-override) (https://expressjs.com/en/resources/middleware/method-override.html) 
 
-// Sets up session and connect to our Sequelize db
+// Sets up session and connect to our Sequelize db store (sequelize) instead of cookie store (memory) (https://expressjs.com/en/guide/behind-proxies.html) 
 const sess = { // session settings for server and client side files (default is ./controllers/index.js) 
-  secret: 'Super secret secret', // secret key for session cookie
+  secret: 'Super secret secret', // secret key for session cookie (default is 'Super secret secret') 
   cookie: { // session cookie settings for server and client side files (default is ./controllers/index.js)
     maxAge: 30 * 60 * 1000, // 30 minutes (default is 10 minutes)
     httpOnly: true, // default is true (https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#HTTP_only)
@@ -32,9 +32,9 @@ const sess = { // session settings for server and client side files (default is
   }),
 };
 
-app.use(session(sess)); // session settings for server and client side files (default is ./controllers/index.js)
+app.use(session(sess)); // session settings for server and client side files (default is ./controllers/index.js) 
 
-const hbs = exphbs.create(); // initializes handlebars
+const hbs = exphbs.create(); // initializes handlebars (https://handlebarsjs.com/guide/) to handlebars (https://expressjs.com/en/guide/using-template-engines.html)
 
 app.engine('handlebars', hbs.engine); // engine for handlebars (default is ./controllers/index.js)
 app.set('view engine', 'handlebars'); // view engine for handlebars (default is ./controllers/index.js)
@@ -43,10 +43,10 @@ app.use(express.json()); // for parsing json data (https://expressjs.com/en/api.
 app.use(express.urlencoded({ extended: false })); // for parsing url encoded data (https://expressjs.com/en/api.html#express.urlencoded)
 app.use(express.static(path.join(__dirname, 'public'))); // for serving static files (https://expressjs.com/en/starter/static-files.html)
 
-app.use(routes); // routes for server and client side files (default is ./controllers/index.js)
+app.use(routes); // routes for server and client side files (default is ./controllers/index.js) 
 
 app.use((req, res, next) => { // middleware for checking if user is logged in or authenticated via session store (https://expressjs.com/en/guide/behind-proxies.html)
-  // List of paths that do not require authentication
+  // List of paths that do not require authentication (https://expressjs.com/en/guide/behind-proxies.html)
   const authFreePaths = ['/login', '/signup', '/logout', '/css/', '/js/']; // paths that do not require authentication (https://expressjs.com/en/guide/behind-proxies.html)
   if (!req.session.userId && !authFreePaths.some(path => req.path.startsWith(path))) { // if user is not logged in and path is not in authFreePaths list then redirect to login
     return res.redirect('/login'); // redirect to login page (https://expressjs.com/en/guide/behind-proxies.html)
@@ -55,9 +55,9 @@ app.use((req, res, next) => { // middleware for checking if user is logged in or
 });
 
 
-// middleware for checking if session has expired
+// middleware for checking if session has expired and if so then destroy session and redirect to login page (https://expressjs.com/en/guide/behind-proxies.html)
 app.use((req, res, next) => { // middleware for checking if session has expired (https://expressjs.com/en/guide/behind-proxies.html)
-  if (req.session.expires && Date.now() > req.session.expires) { // if session has expired then destroy session and redirect to login
+  if (req.session.expires && Date.now() > req.session.expires) { // if session has expired then destroy session and redirect to login page (https://expressjs.com/en/guide/behind-proxies.html)
     req.session.destroy(() => { // destroy session and redirect to login page (https://expressjs.com/en/guide/behind-proxies.html)
       res.redirect('/login'); // redirect to login page (https://expressjs.com/en/guide/behind-proxies.html)
     });
@@ -66,20 +66,20 @@ app.use((req, res, next) => { // middleware for checking if session has expired
   }
 });
 
-// refreshes expiration time so site doesn't log out active users
+// refreshes expiration time so site doesn't log out active users (https://expressjs.com/en/guide/behind-proxies.html) 
 app.use((req, res, next) => { // middleware for checking if session has expired (https://expressjs.com/en/guide/behind-proxies.html)
   if (req.session.expires) {   
     const extendedExpirationTime = new Date(Date.now() + 30 * 60 * 1000); // 30 minutes (30 * 60 * 1000) = 30 minutes (default is 10 minutes)
-    req.session.expires = extendedExpirationTime; // refreshes expiration time so site doesn't log out active users
+    req.session.expires = extendedExpirationTime; // refreshes expiration time so site doesn't log out active users (https://expressjs.com/en/guide/behind-proxies.html)
   }
   next(); // next middleware (https://expressjs.com/en/guide/behind-proxies.html)
 });
 
  // middleware for checking if user is logged in or authenticated via session store (https://expressjs.com/en/guide/behind-proxies.html)
 sequelize.sync({ force: false }).then(() => {   // syncs sequelize with db (default is ./config/connection.js)
-  app.listen(PORT, () =>    // listens on port 3001 (default is 3001)
+  app.listen(PORT, () =>    // listens on port 3001 (default is 3001) 
     console.log( 
-      `\nServer running on port ${PORT}. Visit http://localhost:${PORT} and create an account!`
+      `\nServer running on port ${PORT}. Visit http://localhost:${PORT} and create an account!` // logs server running on port 3001 (default is 3001) (https://expressjs.com/en/guide/behind-proxies.html
     )
   );
 });