Randomly assign gifts for Xmas

gifts.js

const fs = require('fs');

Array.prototype.flat = function () {
  return this.reduce((acc, val) => acc.concat(val), []);
};

const participants = [
  'Nicolas',
  'Mariette',
  'Thomas',
  'Charline',
  'Jojo',
  'Marine',
  'Axelle',
  'Justine',
  'Natacha',
  'Lili',
  'Sylvain',
  'Julie',
  'Christophe',
  'Fech',
  'Hadrien',
  'Noemie',
  'Roland',
  'M. Pascale',
  'Mathieu',
  'Clement',
  'Florent',
  'Aurélie',
  'Clara',
  'Margaux',
  'Romain',
  'Kathy',
  'Simon',
];

const notCompatibles = [
  ['Nicolas', 'Mariette', 'Thomas', 'Charline'],
  ['Jojo', 'Marine', 'Axelle', 'Justine'],
  ['Sylvain', 'Julie', 'Christophe'],
  ['Fech', 'Hadrien', 'Noemie'],
  ['M. Pascale', 'Mathieu', 'Clement'],
  ['Florent', 'Aurélie', 'Clara', 'Margaux'],
  ['Romain', 'Kathy', 'Simon'],
];

const toExclude = giver =>
  notCompatibles
    .filter(notCompatible => notCompatible.includes(giver))
    .flat();

const randomIndex = (length, minIndex = 0) =>
  Math.floor(Math.random() * length) + minIndex;

const pickRandomly = (arr) => arr[randomIndex(arr.length)];

const pickRandomlyWithException = (arr, exceptedValues) => {
  const arrWithoutException = arr.filter(el => !exceptedValues.includes(el));
  return pickRandomly(arrWithoutException);
};

let receivers = [...participants];
const gifts = participants.map((giver, index) => {
  // pick in left receivers except the current giver
  const receiver = pickRandomlyWithException(receivers, [...toExclude(giver), giver]);

  // remove receiver from the left receivers
  receivers = receivers.filter(el => el !== receiver);

  // return the couple giver/receiver
  return { giver, receiver };
});

fs.writeFile('/Users/thomas/Desktop/cadeaux_noel/result.txt', JSON.stringify(gifts, null, 2), () => {
  console.log('The drawing lots is done');
});