0xD34F

не надо код, подскажите алгоритм

function shorten(val) {
  if (val <= 10000) {
    return val.toString();
  }

  const thousands = val / 1000;
  const rounded = Math.round(thousands);
  const deviation = Math.sign(thousands - rounded);

  return `${[ '≈', '', '>' ][deviation + 1]}${rounded} т.`;
}

Цена завернута в див price prc-new

$('input').on('input', function() {
  $(this).val((i, v) => Math.max(this.min, Math.min(this.max, v)));
});

document.querySelector('input').addEventListener('input', ({ target: t }) => {
  t.value = Math.max(t.min, Math.min(t.max, t.value));
});

$('.price').text((i, text) => {
  const [ price, currency ] = text.split(' ');
  return `${(+price).toLocaleString()} ${currency}`;
});

// или

document.querySelectorAll('.price').forEach(n => {
  n.textContent = n.textContent.replace(/\d(?=(\d{3})+\D)/g, '$& ');
});

function toggleClasses(block) {
  const info = block.querySelector('.infoWrapper');
  block.classList.toggle('marginBottom10');
  block.classList.toggle('marginBottom120');
  info.classList.toggle('displayNone');
  info.classList.toggle('displayBlock');
}

document.addEventListener('click', function(e) {
  const block = e.target.closest('.blockSvg');
  if (block) {
    const prevBlock = document.querySelector('.blockSvg.marginBottom120');
    if (prevBlock && prevBlock !== block) {
      toggleClasses(prevBlock);
    }

    toggleClasses(block);
  }
});

const className = 'dop_atr';
const maxlen = 250;

$(`.${className}`).text((i, text) => {
  return text[maxlen] ? `${text.substring(0, maxlen)}...` : text;
});

for (const n of document.getElementsByClassName(className)) {
  n.innerText = n.innerText.slice(0, maxlen) + (n.innerText.charAt(maxlen) && '...');
}

// или

document.querySelectorAll(`.${className}`).forEach(function(n) {
  n.textContent = n.textContent.replace(this, '$1...');
}, RegExp(`(.{${maxlen}}).+`));

document.addEventListener('click', function(e) {
  const el = document.getElementById(e.target.dataset.id);
  if (el) {
    el.checked = !el.checked;
  }
});

const buttons = document.querySelectorAll('[data-id]');
const onClick = e => checkboxes[e.target.dataset.id].checked ^= 1;
const checkboxes = Array
  .from(buttons, n => n.dataset.id)
  .reduce((acc, n) => (acc[n] = document.querySelector(`#${n}`), acc), {});

buttons.forEach(n => n.addEventListener('click', onClick));

$('.tab__list').on('click', '.tab__item', function() {
  const
    $this = $(this),
    { label, ...attrs } = text[$this.data('tab')];

  $this.siblings().removeClass('tab__item--active');
  $this.addClass('tab__item--active');
  $('#formField').attr(attrs);
  $('#formLabel').text(label);
});

.red{border:3px solid red;;}
.green{border:3px solid red;;}

.items-list-item-colors label {
  border: 3px solid red;
}

.items-list-item-colors label.active {
  border-color: green;
}

const containerSelector = '.items-list-item-colors';
const itemSelector = 'label';
const activeClass = 'active';

$(containerSelector).change(function() {
  $(itemSelector, this)
    .removeClass(activeClass)
    .has(':checked')
    .addClass(activeClass);
});

// или

document.querySelectorAll(containerSelector).forEach(n => {
  n.addEventListener('change', onChange);
});

function onChange({ target: t }) {
  this.querySelectorAll(itemSelector).forEach(n => {
    n.classList.toggle(activeClass, n.contains(t));
  });
}

// или

document.addEventListener('change', e => {
  const item = e.target.closest(itemSelector);
  if (item) {
    item.closest(containerSelector).querySelectorAll(itemSelector).forEach(n => {
      n.classList.toggle('active', n === item);
    });
  }
});

const $inner = $('.inner');
if (!$inner.find('.butt_back').length) {
  $inner.append(...);
}

$('.inner')
  .find('.butt_back').remove()
  .end()
  .append(...);

Что не так ?

canvas = document.getElementById('myCanvas');
<...>
drawImage(canvas[0],

$(window).scroll(function onScroll() {
  const $this = $(this);
  if ($this.scrollTop() > scrollToElem) {
    $('#popup-item').addClass('popup-open');
    $this.off('scroll', onScroll);
  }
});

document.addEventListener('mouseover', ({ target: t }) => {
  if (t.classList.contains('pic') && !t.dataset.interval) {
    t.dataset.interval = bgRotate(t);
  }
});

document.addEventListener('mouseout', ({ target: t }) => {
  const { interval } = t.dataset;
  if (interval) {
    clearInterval(interval);
    delete t.dataset.interval;
  }
});

document.querySelectorAll('.pic').forEach(n => {
  n.addEventListener('mouseenter', onHover);
  n.addEventListener('mouseleave', onHover);
});

function onHover({ type, target: t }) {
  const d = t.dataset;
  if (type === 'mouseenter' && !d.interval) {
    d.interval = bgRotate(t);
  } else if (type === 'mouseleave') {
    clearInterval(d.interval);
    delete d.interval;
  }
}

.images_box a {
  display: none;
}

.images_box a.active {
  display: inline;
}

const containerSelector = '.items-list-item-wrapper';
const buttonSelector = '.items-list-item-colors input';
const contentSelector = '.images_box a';
const activeClass = 'active';


// jquery, как вы и хотели
$(containerSelector).on('change', buttonSelector, function(e) {
  $(contentSelector, e.delegateTarget)
    .removeClass(activeClass)
    .eq($(buttonSelector, e.delegateTarget).index(this))
    .addClass(activeClass);
}).each((i, n) => $(buttonSelector, n).first().click());

// или, к чёрту jquery
document.querySelectorAll(containerSelector).forEach(n => {
  n.addEventListener('change', onChange);
  n.querySelector(buttonSelector).click();
});

function onChange({ target: t }) {
  if (t.matches(buttonSelector)) {
    const buttons = this.querySelectorAll(buttonSelector);
    const index = Array.prototype.indexOf.call(buttons, t);
    this.querySelectorAll(contentSelector).forEach((n, i) => {
      n.classList.toggle(activeClass, i === index);
    });
  }
}

function navFunction(id) {
  for (const n of document.querySelectorAll('.dropdown2-content')) {
    n.classList[n.id === id ? 'toggle' : 'remove']('show');
  }
}

.dropdown2 .dropdown2-content {
  display: none;
}

.dropdown2.show .dropdown2-content {
  display: block;
}

const containerSelector = '.dropdown2';
const buttonSelector = `${containerSelector} .dropbtn2`;
const activeClass = 'show';


// делегирование, назначаем обработчик клика один раз для всех кнопок
document.addEventListener('click', e => {
  const button = e.target.closest(buttonSelector);
  if (button) {
    document.querySelectorAll(containerSelector).forEach(function(n) {
      n.classList[n === this ? 'toggle' : 'remove'](activeClass);
    }, button.closest(containerSelector));
  }
});

// или, назначаем обработчик клика каждой кнопке индивидуально
const onClick = function({ currentTarget: t }) {
  this.forEach((n, i) => n.classList[n.contains(t) ? 'toggle' : 'remove'](activeClass));
}.bind(document.querySelectorAll(containerSelector));

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

const inputSelector = '#icons_care';
const checkboxSelector = '.check_care';
const checkboxCheckedSelector = `${checkboxSelector}:checked`;
const dataAttr = 'icon';
const separator = ', ';

$(document).on('change', checkboxSelector, () => {
  $(inputSelector).val($(checkboxCheckedSelector)
    .get()
    .map(n => $(n).data(dataAttr))
    .join(separator)
  );
});

// или

document.addEventListener('change', e => {
  if (e.target.matches(checkboxSelector)) {
    const input = document.querySelector(inputSelector);
    const cb = document.querySelectorAll(checkboxCheckedSelector);
    input.value = Array.from(cb, n => n.dataset[dataAttr]).join(separator);
  }
});

const buttonSelector = '.button';
const blockSelector = '.div';
const activeClass = 'red';

function toggleBlock(blocks, buttons, button) {
  const index = Array.prototype.indexOf.call(buttons, button);
  blocks.forEach((n, i) => {
    n.classList[i === index ? 'toggle' : 'remove'](activeClass);
  });
}


// обработчик клика делегированный, назначается один раз
document.addEventListener('click', e => {
  const button = e.target.closest(buttonSelector);
  if (button) {
    const blocks = document.querySelectorAll(blockSelector);
    const buttons = document.querySelectorAll(buttonSelector);
    toggleBlock(blocks, buttons, button);
  }
});

// или, назначаем обработчик клика каждой кнопке индивидуально
const buttons = document.querySelectorAll(buttonSelector);
const blocks = document.querySelectorAll(blockSelector);
const onClick = e => toggleBlock(blocks, buttons, e.currentTarget);
buttons.forEach(n => n.addEventListener('click', onClick));

<input class="date">
<input class="date">
<input class="date">

const yearButton = year => `
  <button
    data-year="${year}"
    class="ui-datepicker-current ui-state-default ui-priority-secondary ui-corner-all"
  >${year}</button>
`;

$('.date').datepicker({
  showButtonPanel: true,
}).each(function(i) {
  $(this).datepicker(
    'option',
    'currentText',
    `Today ${yearButton(2015 + i * 2)}${yearButton(2015 + i * 2 + 1)}`
  );
});

$(document).on('click', '[data-year]', function() {
  $.datepicker._curInst.input.datepicker('setDate', `01/01/${$(this).data('year')}`);
});