app.js

//How to export and require modules with NODE JS
const fs = require("fs");

//const f = require("./module1.js")
// const mod = require("./module1");
const { f, P } = require("./module1");
//const y = require("./module2/bubba.js");
//const y = require("./module2/bubba");
const y = require("./module2");

f();
//mod.x();
console.log(P);

y();

bubba.js

const y = function() {
  console.log("function y");
};
const PIE = 3.14;

module.exports = y;

module1.js

const f = function() {
  console.log("This is function f inside module1.js");
};
const x = function() {
  console.log("This is function x inside module1.js");
};
const P = 3.14;

//module.exports = f;
// module.exports.f = f;
// module.exports.x = x;
// module.exports.P = P;
module.exports = { f, x, P };

package.json

{
  "name": "module2",
  "version": "1.0.0",
  "description": "",
  "main": "bubba.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}