0xD34F

const obj = Object.assign({}, ...arr.map((n, i) => ({ [n]: arr2[i] })));
// или
const obj = arr.reduce((acc, n, i) => ({ ...acc, [n]: arr2[i] }), {});

const combine = (keys, values) =>
  keys.reduce((acc, n, i) => (acc[n] = values[i], acc), {});


const obj = combine(arr, arr2);

$(document).on('click', '.ev-title', function() {
  $(this).closest('.wrapper').find('.dop-descr').toggleClass('visible');
});

const containerSelector = '.wrapper';
const buttonSelector = '.ev-title';
const activeClass = 'active';

$(containerSelector).on('click', buttonSelector, e => {
  $(e.delegateTarget).toggleClass(activeClass);
});

document
  .querySelectorAll(`${containerSelector} ${buttonSelector}`)
  .forEach(n => n.addEventListener('click', onClick));

function onClick() {
  this.closest(containerSelector).classList.toggle(activeClass);
}

больше не появлялось пока он не почистит куки

export default { ...test1, ...test2 };

// или

export default Object.assign({}, test1, test2);

// или

export default ((merged, ...objs) => {
  for (const n of objs) for (const k in n) {
    if (n.hasOwnProperty(k) && !merged.hasOwnProperty(k)) {
      merged[k] = n[k];
    }
  }

  return merged;
})({}, test2, test1);

const spinWords = str => str
  .split(' ')
  .map(n => n.length > 4 ? [...n].reverse().join('') : n)
  .join(' ');

function spinWords(str) {
  return str.replace(/\S{5,}/g, m => ''.concat(...Array.from(m).reverse()));
}

const result = Object
  .entries(Object.assign({}, ...arr1, ...arr2))
  .map(n => ({ [n[0]]: n[1] }));

const union = (key, ...arrs) =>
  Object.values([].concat(...arrs).reduce((acc, n) => (acc[key(n)] = n, acc), {}));


const result = union(el => Object.keys(el)[0], arr1, arr2);

const result = _.unionBy(arr1, arr2, el => _.keys(el)[0]);

fetch(url)
  .then(r => r.json().then(data => ({ data, headers: r.headers })))
  .then(r => console.log(r.data, r.headers));

$(document).click(function(e) {
  const $target = $(e.target);
  let $itemsToClose = $('.top-menu__item');

  if ($target.hasClass('top-menu__link')) {
    const $item = $target.closest('li');
    $item.toggleClass('top-menu__item_open').children('ul').slideToggle();
    $itemsToClose = $itemsToClose.not($item);
  }

  $itemsToClose
    .removeClass('top-menu__item_open')
    .children('ul')
    .slideUp();
});

<div class="slide" data-slide="1">1</div>
<div class="slide" data-slide="2">1+1</div>
<div class="slide" data-slide="3">3.0001</div>

<div>
  <span class="step" data-slide="1"></span>
  <span class="step" data-slide="2"></span>
  <span class="step" data-slide="3"></span>
</div>

$(document).on('click', '.step', function() {
  $('.step.active, .slide.active').removeClass('active');
  $(this).addClass('active');
  $(`.slide[data-slide="${this.dataset.slide}"]`).addClass('active');
});

// по умолчанию сделаем активным первый слайд
$('.step').eq(0).click();

Пробовал приспособить setTimeout, пробовал им вызывать функцию, а к функции присвоить название.. Но не сработало..
Что я делаю не так?

#red {
  transition: opacity 0.2s;
}

#red.hidden {
  opacity: 0.5;
}

$('#red').click(e => $(e.target).toggleClass('hidden'));

// или

document.querySelector('#red').addEventListener('click', e => {
  e.target.classList.toggle('hidden');
});

const splitArr = (arr, chunks) =>
  Array.from(
    { length: chunks },
    (_, c) => arr.filter((n, i) => i % chunks === c)
  );

const splitArr = (arr, chunks) =>
  arr.reduce((acc, n, i) => (
    (acc[i % chunks] = acc[i % chunks] || []).push(n),
    acc
  ), []);

const options = [ 'first', 'second', 'third', 'fourth' ];
const $table = $('table');

$('button').click(function() {
  $table.append(`
    <tr>
      <td>
        <select>
          <option disabled selected>-</option>
          ${options.map(n => `<option>${n}</option>`).join('')}
        </select>
      </td>
      <td>
        <button class="del">del</button>
      </td>
    </tr>
  `);

  updateDisabled();
});

$table
  .change(updateDisabled)
  .on('click', '.del', function() {
    $(this).closest('tr').remove();
    updateDisabled();
  });


function updateDisabled() {
  const $select = $table.find('select');
  const selectedOptions = $select.get().map(n => n.value);

  $select.find('option').prop('disabled', function() {
    return selectedOptions.includes(this.value);
  });
}

#xxxten.big {
  width: 300px;
}

document.querySelector('#xxxten').addEventListener('click', function() {
  this.classList.toggle('big');
});

document.querySelector('button').addEventListener('click', function() {
  const bar = document.querySelector('#progress');
  const label = document.querySelector('#procent');

  let width = 0;
  const interval = setInterval(function() {
    if (++width >= 100) {
      clearInterval(interval);
    }

    bar.style.width = label.innerText = `${width}%`;
  }, 10);
});

document.querySelectorAll('.news-item_title').forEach(n => {
  n.querySelector('.tit_link').textContent = '[Подробнее]';
  n.closest('.news-block_item').append(n);
});

for (const n of document.getElementsByClassName('tit_link')) {
  n.innerText = '[Подробнее]';
  n.parentNode.parentNode.appendChild(n.parentNode);
}

const items = document.querySelector('.news-block_wrap').children;
for (let i = 0; i < items.length; i++) {
  items[i].children[1].children[0].innerHTML = '[Подробнее]';
  items[i].insertAdjacentElement('beforeend', items[i].children[1]);
}

function updateSum() {
  const sum = $('.order-table .number').get().reduce((acc, n) => {
    const price = +$(n).prev().text().replace(',', '.');
    const count = +$('input', n).val();
    return acc + price * count;
  }, 0);

  $('.order-end-form input[type="text"]').val(sum.toFixed(2));
}

$('.order-table')
  .on('click', '.plus, .minus', function() {
    const change = $(this).hasClass('plus') ? 1 : -1;
    $(this).siblings('input').val((i, val) => Math.max(0, +val + change));
    updateSum();
  })
  .on('input', '.number input', function() {
    $(this).val((i, val) => Math.max(0, val | 0));
    updateSum();
  });