countdown.js

function getCountdown() {
  // diff in seconds, comes through function's params
  const diff = 60*60*24*4 + 60*60*22 + 60*35 + 5;
  const MINUTE = 60;
  const HOUR = MINUTE * 60;
  const DAY = HOUR * 24;

  const days = Math.floor(diff / DAY);
  const hDiff = diff % DAY;
  const hours = Math.floor(hDiff / HOUR);
  const mDiff = hDiff % HOUR;
  const minutes = Math.floor(mDiff / MINUTE);
  const seconds = mDiff % MINUTE;

  return [days, hours, minutes, seconds]
    .map(v => (''+v)[1] ? ''+v : '0'+v)
}

// output: ["04", "22", "35", "05"]

sortfn.js

const sortFn = (propPath, isReverse = false) => (objA, objB) => {
  // lodash dependency
  const a = _.get(objA, propPath);
  const b = _.get(objB, propPath);
  const isNumbers = (typeof a === 'number') && (typeof b === 'number');
  const isStrings = (typeof a === 'string') && (typeof b === 'string');
  const isDates = (a instanceof Date) && (b instanceof Date);
  
  if (isNumbers || isDates) {
    return isReverse ? b - a : a - b
  } else if (isStrings) {
    return isReverse ? b.localeCompare(a) : a.localeCompare(b)
  } else {
    return 0; // don't know how to compare so equals
  }
}

// array to sort
const arr = [
  {num: 1, str: 'ddd', date: new Date('2008-12-17T03:24:00'), nested: {num: 4}},
  {num: 5, str: 'zzz', date: new Date('2000-12-17T03:24:00'), nested: {num: 2}},
  {num: 2, str: 'aaa', date: new Date('2018-12-17T03:24:00'), nested: {num: 9}},
]

console.log({
  byNumber:    [...arr].sort(sortFn('num')),
  byNumberRev: [...arr].sort(sortFn('num', true)),
  byString:    [...arr].sort(sortFn('str')),
  byStringRev: [...arr].sort(sortFn('str', true)),
  byDate:      [...arr].sort(sortFn('date')),
  byDateRev:   [...arr].sort(sortFn('date', true)),
  byNested:    [...arr].sort(sortFn('nested.num')),
  byNestedRev: [...arr].sort(sortFn('nested.num', true))
});

stripe-plans.js

// https://stripe.com/docs/billing/subscriptions/tiers

/*
plans = [
   {upTo: 10, price: 5},
   {upTo: 25, price: 4},
   {upTo: 50, price: 3},
   {upTo: null, price: 2}
]
for 15 users = 10 * 5 + 5 * 4
for 30 users = 10 * 5 + 15 * 4 + 5 * 3
for 57 users = 10 * 5 + 15 * 4 + 25 * 3 + 7 * 2
*/

function getTotal(plans, num) {
  return plans.reduce((acc, cur) => {
    var quota = cur.upTo ? cur.upTo - acc.prev : Number.MAX_SAFE_INTEGER;
    var n = acc.rest - quota;
    acc.sum += cur.price * (n > 0 ? quota : acc.rest);
    acc.rest = n > 0 ? n : 0;
    acc.prev = cur.upTo;
    return acc;
  }, {sum: 0, prev: 0, rest: num}).sum
}