Divide any number/string every nth characters

string-divider.js

const divide = (str, divider, n) => String(str)
  .split('')
  .reverse()
  .reduce((acc, cv, i) => cv + (i % n === 0 ? divider : '') + acc);

let num = 4000000;
divide(num, '|', 2); // 4|00|00|00
divide(num, ',', 3); // 4,000,000
divide(num, '-', 1); // 4-0-0-0-0-0-0

let cc = 1000200030004000;
divide(cc, '-', 4); // 1000-2000-3000-4000