JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
</ul>

JavaScript

(function () {
    var secundarios = [];
    var ul = document.querySelector('ul');
    var lis = ul.querySelectorAll('li');
    [].forEach.call(lis, function (el, i) {
        if (i % 2 != 0) return;
        var removido = ul.removeChild(el);
        secundarios.push(removido);
    });
    [].forEach.call(secundarios, function (el) {
        ul.appendChild(el);
    });
})();