Make a function that returns a number, starting with 1, increasing that number by 1 with each call of the function

counter1.ts

// just using the module as the closure

let count = 1;

export function counter() {
  return count++;
}

counter2.ts

// Using a function to create a function with a counting variable
// scope accessible

function countingClosureCreator(startingNumber = 1) {
  let count = startingNumber;
  return function counter() {
    return count++;
  };
}

export const counter = countingClosureCreator();

counter3.ts

// just like counter2 but uses a self-executing
// function closure and arrow functions

export const counter = (() => {
  let count = 1;
  return () => count++;
})();

counter4.ts

// Uses iterators for fun and profit
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function*

function createInfiniteCountingIterator(startingNumber = 1) {
  function* counterGenerator() {
    let count = 1;
    while (true) {
      yield count++;
    }
  }

  const iteratorInstance = counterGenerator();

  return iteratorInstance;
}

const infiniteCountingIterator = createInfiniteCountingIterator();

export const counter = (() => {
  return infiniteCountingIterator.next().value;
})();

implementation.ts

import { counter } from './counter';

console.log(counter()); // 1
console.log(counter()); // 2
console.log(counter()); // 3
console.log(counter()); // 4