0xD34F

menu.addEventListener('click', ({ target: t }) => {
  if (t.tagName === 'SPAN') {
    const parent = t.parentNode;
    parent.classList.toggle('active');
    for (const n of menu.querySelectorAll('.active')) {
      if (n !== parent) {
        n.classList.toggle('active', n.contains(parent));
      }
    }
  }
});

- .menu_list_item.active .submenu {
+ .active > .submenu {

- .submenu_list_item.active .product {
+ .active > .product {

const container = document.querySelector('#menu');
const itemSelector = 'li';
const buttonSelector = `${itemSelector} span`;
const activeClass = 'active';

container.addEventListener('click', function(e) {
  const item = e.target.closest(buttonSelector)?.closest(itemSelector);
  if (item) {
    item.classList.toggle(activeClass);
    this.querySelectorAll(`.${activeClass}`).forEach(n => {
      if (n !== item) {
        n.classList.toggle(activeClass, n.contains(item));
      }
    });
  }
});

const items = document.querySelectorAll('.faq__input');
const onChange = ({ target: t }) => t
  .closest('.faq__items')
  .querySelectorAll('.faq__question--top')
  .forEach(n => n.classList.toggle('active', n.nextElementSibling.checked));

items.forEach(n => n.addEventListener('change', onChange));

const itemSelector = '.faq__item';
const radioSelector = '.faq__input';
const activeClass = 'active';
const toggleActiveClass = radioGroupName => document
  .querySelectorAll(`${radioSelector}[name="${radioGroupName}"]`)
  .forEach(n => n.closest(itemSelector).classList.toggle(activeClass, n.checked));

document.querySelectorAll(radioSelector).forEach(function(n) {
  n.addEventListener('change', this);
}, e => toggleActiveClass(e.target.name));

document.addEventListener('change', ({ target: t }) => {
  if (t.matches(radioSelector)) {
    toggleActiveClass(t.name);
  }
});

const result = array2.filter(function(n) {
  return this.has(n.code);
}, new Set(array1.map(n => n.value)));

const obj2 = Object.fromEntries(array2.map(n => [ n.code, n ]));
const result = array1.reduce((acc, n) => ((n = obj2[n.value]) && acc.push(n), acc), []);

const result = array2.filter(n => array1.some(m => m.value === n.code));

e.target.dataset.followerStyle

Object.values(arr.reduce((max, n) => (
  max[n.group] = max[n.group]?.score > n.score ? max[n.group] : n,
  max
), {}))

// значения withSeat вместо раскладывания в отдельные переменные собираете в объект
const withSeat = {
  adult: 1,
  teenager: 1,
  babe: 0,
};


const passengers = cabins.flatMap(n => Object
  .entries(n)
  .flatMap(([ k, v ]) => Array.from(
    { length: v },
    () => ({ withSeat: withSeat[k] })
  ))
);

arr.reduce((acc, n, i, a) => (
  a[i - 1]?.name[0] !== n.name[0] && acc.push({ name: n.name[0] }),
  acc.push(n),
  acc
), [])

arr.flatMap((n, i, a) =>
  i && a[~-i].name[0] === n.name[0]
    ? n
    : [ { name: n.name[0] }, n ]
)

const obj = Object.fromEntries(Object
  .entries(arr
    .flatMap(Object.entries)
    .reduce((acc, n) => ((acc[n[0]] ??= new Set).add(n[1]), acc), {}))
  .map(([ k, v ]) => [ k, v.size === 1 ? [...v][0] : null ])
);

const obj = arr.reduce((acc, n) => (
  Object.keys(n).forEach(k => {
    acc[k] = Object.hasOwn(acc, k) && n[k] !== acc[k] ? null : n[k];
  }),
  acc
), {});

formatDate(date) {
  const today = new Date();
  return [ 'getFullYear', 'getMonth', 'getDate' ].every(n => date[n]() === today[n]())
    ? 'Today'
    : flatpickr.formatDate(date, 'j M');
},

const groupSelector = 'fieldset.js-tree-box';
const mainSelector = 'legend input';
const itemSelector = 'legend + span input';
const activeClass = 'active';

document.addEventListener('change', ({ target: t }) => {
  const group = t.closest(groupSelector);
  if (group) {
    const main = group.querySelector(mainSelector);
    const items = [...group.querySelectorAll(itemSelector)];

    if (main === t) {
      items.forEach(n => n.checked = t.checked);
    } else {
      const numChecked = items.reduce((acc, n) => acc + n.checked, 0);
      main.checked = numChecked === items.length;
      main.indeterminate = 0 < numChecked && numChecked < items.length;
    }

    group.classList.toggle(activeClass, main.checked);
  }
});

const sorted = (data, key) => Array
  .from(data, n => [ n, key(n) ])
  .sort((a, b) => a[1] - b[1])
  .map(n => n[0]);


document.querySelector('.result').append(...sorted(
  document.querySelector('.data').cloneNode(true).children,
  n => +n.innerText
));

делегирование не работает

в консоли выдает "e.target.closest is not a function"

const hoverCellNum = hoverCell.getAttribute('data-tdnum');

document.addEventListener('mouseenter', ({ target: t }) => {
  if (t.matches?.('td._hight-light__cell')) {
    t.closest('tbody').querySelectorAll('.table-big__row').forEach(n => {
      n.cells[t.cellIndex].classList.add('_hover');
    });
  }
}, true);

document.addEventListener('mouseleave', e => {
  if (e.target.matches?.('td._hight-light__cell')) {
    document.querySelectorAll('._hover').forEach(n => n.classList.remove('_hover'));
  }
}, true);

document.addEventListener('click', updateCounter);
document.addEventListener('input', updateCounter);

document.querySelectorAll('.tariff__counter').forEach(n => {
  const max = n.dataset.seats;
  n.querySelectorAll('.tariff__counter-max').forEach(m => m.innerText = max);
  n.querySelectorAll('.amount').forEach(m => m.max = max);
  n.querySelectorAll('button').forEach(m => m.dataset.change = m.innerText === '+' ? 1 : -1);
});

function updateCounter({ target: t }) {
  const input = t.closest('.tariff__counter-block')?.querySelector('.amount');
  if (input) {
    const { min, max, value } = input;
    input.value = Math.max(min, Math.min(max, (value | 0) + (t.dataset.change | 0)));
  }
}

const keys = [ 'id', 'secondId' ];
const result = firstArray.map(n => secondArray.find(m => keys.every(k => n[k] === m[k])) ?? n);

const arrToTree = (arr, keys) =>
  arr.reduce((acc, n) => (
    keys.reduce((p, c, i) => p[n[c]] ??= i + 1 === keys.length ? n : {}, acc),
    acc
  ), {});


const keys = [ 'id', 'secondId' ];
const tree = arrToTree(secondArray, keys);
const result = firstArray.map(n => keys.reduce((p, c) => p?.[n[c]], tree) ?? n);

const arrToTree = (arr, keys) =>
  arr.reduce((acc, n) => (
    keys(n).reduce(
      (p, c, i, a) => p.set(c, p.get(c) ?? (-~i === a.length ? n : new Map)).get(c),
      acc
    ),
    acc
  ), new Map);


const keys = n => [ n.id, n.secondId ];
const result = firstArray.map(function(n) {
  return keys(n).reduce((p, c) => p?.get(c), this) ?? n;
}, arrToTree(secondArray, keys));

function getLeaves(tree) {
  const result = [];

  for (const stack = [...tree]; stack.length;) {
    const n = stack.pop();
    if (Array.isArray(n.children) && n.children.length) {
      stack.push(...n.children);
    } else {
      result.push(n);
    }
  }

  return result.reverse();
}

function getLeaves(tree) {
  const result = [];
  const stack = [];

  for (let arr = tree, i = 0; i < arr.length || stack.length; i++) {
    if (i === arr.length) {
      [ i, arr ] = stack.pop();
    } else if (arr[i].children instanceof Array && arr[i].children.length) {
      stack.push([ i, arr ]);
      [ i, arr ] = [ -1, arr[i].children ];
    } else {
      result.push(arr[i]);
    }
  }

  return result;
}

function getLeaves([...tree]) {
  for (let i = 0; i < tree.length; i++) {
    const c = tree[i].children;
    if (c?.constructor === Array && c.length) {
      tree.splice(i--, 1, ...c);
    }
  }

  return tree;
}

const groupSum = (arr, idKey, ...sumKeys) =>
  Object.values(arr.reduce((acc, n) => (
    acc[n[idKey]] ??= sumKeys.reduce((group, k) => (group[k] = 0, group), {...n}),
    sumKeys.forEach(k => acc[n[idKey]][k] += n[k]),
    acc
  ), {}));


const result = groupSum(arr, 'product', 'price', 'selling_price', 'quantity');