0xD34F

<div>
  <button data-step="-1">-</button>
  <button data-step="+1">+</button>
</div>
<textarea cols="30" rows="10"></textarea>

const history = JSON.parse(localStorage.getItem('history')) || [];
let index = history.length - 1;

const $text = $('textarea').change(function() {
  index = history.push($text.val()) - 1;
  localStorage.setItem('history', JSON.stringify(history));
});

$('[data-step]').click(function() {
  goTo(index + +this.dataset.step);
});

goTo(index);

function goTo(newIndex) {
  if (0 <= newIndex && newIndex <= history.length - 1) {
    index = newIndex;
    $text.val(history[index]);
  }
}

$('.block').on('mouseout', function() {
  this.style.transform = '';
});

arr.map(id => people.find(n => n.id === id))

// или

arr.map(function(n) {
  return this[n];
}, people.reduce((acc, n) => (acc[n.id] = n, acc), {}))

people.filter(n => arr.includes(n.id))

// или

people.filter(((ids, n) => ids.has(n.id)).bind(null, new Set(arr)))

<ul>
  <li><span>aaa</span></li>
  <li>
    <span>bbb</span>
    <ul>
      <li><span>bbb.1</span></li>
      <li>
        <span>bbb.2</span>
        <ul>
          <li><span>bbb.2.1</span></li>
          <li><span>bbb.2.2</span></li>
        </ul>
      </li>
      <li>
        <span>bbb.3</span>
        <ul>
          <li>
            <span>bbb.3.1</span>
            <ul>
              <li><span>bbb.3.1.1</span></li>
            </ul>
          </li>
        </ul>
      </li>
    </ul>
  </li>
</ul>

document.querySelectorAll('li').forEach(n => {
  const count = ((n.querySelector('ul') || {}).children || []).length;
  n.querySelector('span').textContent += ` (${count})`;
});

document.querySelectorAll('li').forEach(n => {
  const count = n.querySelectorAll('li').length;
  n.querySelector('span').textContent += ` (${count})`;
});

(((lead._embedded.items[0].custom_fields.find(cf => cf.id == PRODUCT_FIELD_ID) || {}).values || {})[0] || {}).value || null

lead._embedded.items[0].custom_fields.find(cf => cf.id == PRODUCT_FIELD_ID)?.values[0].value ?? null

class TestClass {
  constructor() {
    const self = el => self.data.push(el);
    Object.setPrototypeOf(self, TestClass.prototype);

    self.data = [];

    return self;
  }

  toString() {
    return this.data.join('');
  }
}

document.querySelectorAll(`.${className}`).forEach((n, i) => {
  n.innerText = arr[i];
});

// или

for (const [ i, n ] of document.querySelectorAll(`.${className}`).entries()) {
  n.innerHTML = arr[i];
}

// или

arr.forEach(function(n, i) {
  this.item(i).textContent = n;
}, document.getElementsByClassName(className));

// или

const elems = document.getElementsByClassName(className);
for (let i = 0; i < elems.length; i++) {
  elems[i].appendChild(document.createTextNode(arr[i]));
}

$(window).scroll(function onScroll() {
  if ($(this).scrollTop() > 777) {
    $('.div_clone').clone().appendTo('.container2');
    $(this).off('scroll', onScroll);
  }
});

const isAllUnique = (...args) => new Set(args).size === args.length;

console.log(isAllUnique(69, 187, 666)); // true
console.log(isAllUnique(2, 2, 3, 4)); // false
console.log(isAllUnique(...'ABCDA')) // false

const elems = [...document.querySelectorAll('.class1')];
const index = elems.findIndex(n => n.classList.contains('class2'));

const elems = document.querySelectorAll('.class1');
let index = elems.length;
while (--index >= 0 && !elems[index].matches('.class2')) ;

const index = Array.prototype.indexOf.call(
  document.querySelectorAll('.class1'),
  document.querySelector('.class2')
);

<div class="country">
  <input class="country-code">
  <img class="country-flag">
</div>

function updateFlag(el) {
  const country = countries.find(n => !el.value.indexOf(n.code));
  el.closest('.country').querySelector('.country-flag').src = country ? country.flag : '';
}

document.addEventListener('input', function(e) {
  if (e.target.classList.contains('country-code')) {
    updateFlag(e.target);
  }
});

document.querySelectorAll('.country-code').forEach(updateFlag);

const countries = [
  { code: ..., flag: ... },
  { code: ..., flag: ... },
  ...
];

const country = countries.find(n => !inputCode.value.indexOf(n.code));
inputFlag.src = country ? country.flag : '';

<input type="number" min="0" max="100">
<table>
  <tbody></tbody>
</table>

const input = document.querySelector('input');
const table = document.querySelector('table');

input.addEventListener('input', ({ target: t }) => {
  const count = t.value = Math.max(0, t.value | 0);
  const [ tbody ] = table.tBodies;
  const { rows } = tbody;

  for (; rows.length > count; tbody.deleteRow(-1)) ;

  while (rows.length < count) {
    const row = tbody.insertRow();
    row.insertCell().textContent = '#' + rows.length;
    row.insertCell().textContent = Math.random() * 1e3 | 0;
  }
});

// или

input.oninput = function() {
  const count = this.value = Math.max(0, +this.value || 0);
  const tbody = table.querySelector('tbody');
  const rows = tbody.children;

  Array.prototype.slice.call(rows, Math.min(rows.length, count)).forEach(n => n.remove());

  tbody.insertAdjacentHTML('beforeend', Array
    .from({ length: Math.max(0, count - rows.length) }, (n, i) => `
      <tr>
        <td>#${rows.length + i + 1}</td>
        <td>${Math.floor(Math.random() * 1000)}</td>
      </tr>`)
    .join('')
  );
};

const baseWidth = $('.banner').width();

$(window).scroll(function() {
  $('.banner').width(baseWidth + $(this).scrollTop());
});

document.addEventListener('click', function(e) {
  if (!e.target.closest('.tileset-showitems')) {
    tilesetShowListRemove();
  }
});

- .active {
+ .active .box {

const containerSelector = '.tileset-showitems';
const buttonSelector = `${containerSelector} .tileset-showitems-trigger`;
const activeClass = 'active';
const closeAllExcept = container => document
  .querySelectorAll(`${containerSelector}.${activeClass}`)
  .forEach(n => n !== container && n.classList.remove(activeClass));

document.addEventListener('click', ({ target: t }) => {
  const button = t.closest(buttonSelector);
  const container = t.closest(containerSelector);

  if (button) {
    container.classList.toggle(activeClass);
  }

  closeAllExcept(container);
});

window.addEventListener('keydown', e => e.key === 'Escape' && closeAllExcept());

for (const n of el.options) {
  for (const m of elValue) {
    if (n.value === m) {
      n.selected = true;
      break;
    }
  }
}

Array.prototype.forEach.call(
  el,
  n => n.selected = elValue.includes(n.value)
);

el
  .querySelectorAll(elValue.map(n => `[value="${n}"]`))
  .forEach(n => n.selected = true);

а где в верстке у тебя эти точки указаны?

const points = [
  { max:      200, text:  'hello, world!!' },
  { max:      800, text:  'fuck the world' },
  { max: Infinity, text: 'fuck everything' },
];

window.addEventListener('scroll', function() {
  const
    scroll = document.documentElement.scrollTop,
    { text } = points.find(n => n.max >= scroll);

  document.querySelector('.fixed').textContent = text;
});

const newArr = arr.map(function({ ...n }) {
  return this.reduce((acc, k) => (acc[k] = acc[k].toLowerCase(), acc), n);
}, [ 'firstName', 'lastName' ]);

const keys = [ 'firstName', 'lastName' ];
arr.forEach(n => keys.forEach(k => n[k] = n[k].toLowerCase()));

const data = $('table tr')
  .get()
  .map(tr => $('input', tr).get().map(n => $(n).val()))
  .filter(row => row[row.length - 1])
  .map(row => `(${row.map(n => `'${n}'`).join(', ')})`);

const data = Array.prototype.reduce.call(
  document.querySelector('table').rows,
  (acc, { cells, lastElementChild: last }) => (
    last.lastElementChild.value && acc.push(`(${Array
      .from(cells, n => `'${n.lastElementChild.value}'`)
      .join(', ')})`
    ),
    acc
  ),
  []
);