Test the birthday paradox for yourself

birthday-paradox.js

async function getChanceOfMatchingBirthday({
  numberOfPeopleInTheRoom = 23,
  howManyRoomsToAverageBetween = 1e5,
} = {}) {
  let initDate = Date.now();
  let testCount = 0;
  let matchCount = 0;

  while (testCount < howManyRoomsToAverageBetween) {
    if (!(testCount % 5e3) && Date.now() >= initDate + 16) {
      await new Promise((resolve) => setTimeout(resolve, 0));
      initDate = Date.now();
    }
    
    matchCount += +Array.from({ length: numberOfPeopleInTheRoom }, () => Math.ceil(Math.random() * 365))
      .some((num, i, arr) => arr.indexOf(num) !== i);
    testCount += 1;
  }

  return matchCount / testCount;
}