counter.js

const createCounter = function() {
  let count = 0;
  this.click = () => count+=1;
  this.getCount = () => count.toLocaleString();
}
const counter = new createCounter();
counter.click(); //count=1
counter.click(); //count=2
counter.click(); //count=3
counter.count = 78; //still count is 3
console.log(counter.getCount()); // 3
console.log(JSON.stringify(counter)); // {"count":78}