StackOverflow 270800

var mobileItems = document.querySelector('#slide-out .nav-mobile .main-menu');

mobileItems.querySelector('li.menu-item-has-children')
    .insertAdjacentHTML('beforeend', '<i class="mobile-arrows fa fa-chevron-down"></i>');

document.querySelector("li.menu-item-has-children i.mobile-arrows").addEventListener("click", el => {

    if (el.classList.contains("fa-chevron-down")) {
        el.classList.remove('fa-chevron-down');
        el.classList.add('fa-chevron-up');
    } else {
        el.classList.add('fa-chevron-down');
        el.classList.remove('fa-chevron-up');
    }

    el.parentNode.querySelectorAll('ul')[0].classList.toggle('hidden')
})


var mobileItems = document.querySelector( '#slide-out .st-nav-mobile .main-menu' );
mobileItems.querySelector('div.penci-mega-latest-posts').remove();
mobileItems.querySelector('div.mega-cat-content-tab').remove();
mobileItems.querySelector('div.mega-recent-post').remove();
mobileItems.querySelector('div.mega-recent-post').remove();

let elementTemp = mobileItems.querySelector('.mega-cat-wrapper');
elementTemp.parentNode.replaceWith(elementTemp);

let elementTemp = mobileItems.querySelector('.mega-cat-sub-categories');
elementTemp.parentNode.replaceWith(elementTemp);