From Video tutorial about Express JS and the many types of variables and settings

app.js

"use strict";
const express = require("express");
const app = express();
const apples = require("./routes/apples");
const port = process.env.port || 4040;

app.set("views", "./views");
app.set("view engine", "pug");
app.set("custom", "Mandalorian");
app.locals.ihave = "spoken"; //lifetime of application

app.use("/apples", apples);

app.get("/", (req, res) => {
  res.json({ cheeses: ["Cheddar", "Danish Blue", "Mozzarella"] });
});

app.get("/abc", (req, res) => {
  res.render(
    "index",
    { title: "Pugified", who: app.get("custom"), p: port },
    (err, html) => {
      if (err) {
        res.status(500).end(err);
      }
      res.send(html);
    }
  );
});

app.listen(port, err => {
  if (err) {
    console.log("ERROR", err);
    return;
  }
  console.log(`Listening on port ${port}`);
});

apples.js

const express = require("express");
const router = express.Router();

router.use(function(req, res, next) {
  req.newProp = "Baby Yoda rules!";
  next();
});

router
  .route("/fuji")
  .get((req, res) => {
    //handle gets for /apples/fuji
    res.send("GET fuji " + req.newProp);
  })
  .post((req, res) => {
    //handle posts for /apples/fuji
    res.locals.myvar = "some value"; //lifetime of the request
    res.send("POST fuji.");
  });

router
  .route("/empire")
  .get((req, res) => {
    //handle gets for /apples/empire
    req.send("GET empire");
  })
  .post((req, res) => {
    //handle posts for /apples/empire
    req.send("POST empire");
  });

module.exports = router;

index.pug

doctype html
html
  head
    title #{title}
    
  body
    h1 #{title}
    p Some text about #{who}
    p #{settings.custom}
    p I have #{ihave}
    // app.locals.settings.custom
    // app.locals.ihave
    p Page generated for port #{p}