ブラウザのConsoleで結果を確認できます。
<section>
<div class="item">item1</div>
<div class="item circle">item2</div>
<div class="item circle">item3</div>
<div class="item circle">item4</div>
<div class="item">item5</div>
</section>
const items = $('.item').get()
console.log(items.length)
// => 5
const circles = $('.circle').get()
console.log(circles.length)
// => 3
const divs = items.concat(circles)
console.log(divs.length)
// => 8
const uniqueDivs = $.uniqueSort(divs)
console.log(uniqueDivs.length)
// => 5
const numbers = $.uniqueSort([1, 2, 2, 3, 4, 3])
console.log(numbers.length)
// => 5
const fruits = $.uniqueSort(['apple', 'banana', 'apple'])
console.log(fruits.length)
// => 3