Евгений Журов

let link = document.createElement('a');
link.href = "https://localhost8080/somepath/somepath/somepath?param=42#some-hash";

link.protocol // -> https:
link.host     // -> localhost8080
link.pathname // -> /somepath/somepath/somepath
link.hash     // -> #some-hash
link.search   // -> ?param=42

var cartItems = JSON.parse(localStorage.getItem('cart'));
var itemsQuantity = cartItems.length;

const c = a.map((i, el) => ({ selector: `#${el.id}`}));

var a = $("span[id ^= call]"),
c = [];
for (var i = 0; i < a.length; i++) {
  let b = {
    selector:"#" + a.eq(i).attr("id"),
  };

  c.push(b);
}

const a = [ 'a', 'b', 'c', 'd' ];
const b = [ 'a', 'b', 'x', 'y', 'z' ];

const c = a.filter(n => b.indexOf(n) === -1);
// или
const c = a.filter(n => !b.includes(n));

function diff(data1, data2, key = n => n) {
  const getKey = key instanceof Function ? key : n => n[key];
  const keys = new Set(Array.from(data2, getKey));
  return Array.prototype.filter.call(data1, n => !keys.has(getKey(n)));
}


diff([1, 2, 3], [2]) // [1, 3]
diff([{id: 1}, {id: 2}, {id: 3}], [{id: 1}, {id: 3}], 'id') // [{id: 2}]
diff('AbCdE', 'aBc', n => n.toLowerCase()) // ['d', 'E']

$(function() {
function getRandomElems($el) {
    $("#b").html("");
    var $li = $el.siblings();
    $li.length < 3 && ($li = $li.add($el));
    $li = $li.get();
    for (var i = 0; i < 3; i++) {
        var rand = (Math.random() * $li.length) | 0;
        $($li.splice(rand,1)).clone().appendTo($("#b"));
    }
}

$("#a").on('click', 'li', function() {
    getRandomElems($(this));
});
});

const sourceSelector = '#a';
const targetSelector = '#b';
const itemSelector = 'li';
const count = 3;

const random = arr => arr.splice(Math.random() * arr.length | 0, 1)[0];

$(sourceSelector).on('click', itemSelector, function() {
  const items = $(this).siblings().clone().get();
  $(targetSelector).html([...Array(count)].map(random.bind(null, items)));
});

// или

const source = document.querySelector(sourceSelector);
const target = document.querySelector(targetSelector);
source.addEventListener('click', ({ target: t }) => {
  if (t = t.closest(itemSelector)) {
    const items = [...source.querySelectorAll(itemSelector)].filter(n => n !== t);
    target.innerHTML = '';
    target.append(...Array.from(
      { length: Math.min(items.length, count) },
      () => random(items).cloneNode(true)
    ));
  }
});

если в списке всего три элемента - все три и выводятся

const items = $(itemSelector, sourceSelector).clone().get();
if (items.length > count) {
  items.splice($(this).index(), 1);
}

// или

const items = [...source.querySelectorAll(itemSelector)];
if (items.length > count) {
  items.splice(items.indexOf(t), 1);
}

<div id="list">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
  <div class="item">4</div>
  <div class="item">5</div>
  <div class="item">6</div>
<div>

const $items = $('#list .item').click(function() {
  console.log($items.not(this).slice(0, 3).toArray());
});

// или

$('#list').on('click', '.item', function() {
  console.log($(this).siblings().slice(0, 3).get());
});