counter.js

// lib/counter.js

var counter = 1;

function increment() {
  counter++;
}

function decrement() {
  counter--;
}

module.exports = {
  counter: counter,
  increment: increment,
  decrement: decrement
};


// src/main.js

var counter = require('../../lib/counter');

counter.increment();
console.log(counter.counter); // 1

counter.counter will have value of 2