JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <li>A</li>
  <li class="target">B</li>
  <li>C</li>
</ul>

<input type="text" value="3">
<button>Bをリストの上にn件追加</button>

JavaScript

$('button').click(function(){
	const n = $('input').val();
	for (let i = 1; i < n; i++){
		$('ul').prepend( $('.target') );
	}
});