JSFiddle - React, Tailwind, and code Playground

CSS

.test {
    background: green;
}

JavaScript

(function () {
    
    var apollo = {};
    var hasClass, addClass, removeClass, toggleClass;
    
    if ('classList' in document.documentElement) {
        hasClass = function () {
            return elem.classList.contains(className);
        };
        addClass = function (elem, className) {
            elem.classList.add(className);
        };
        removeClass = function (elem, className) {
            elem.classList.remove(className);
        };
        toggleClass = function (elem, className) {
            elem.classList.toggle(className);
        };
    } else {
        hasClass = function (elem, className) {
            return new RegExp('(^|\\s)' + className + '(\\s|$)').test(elem.className);
        };
        addClass = function (elem, className) {
            if (!hasClass(elem, className)) {
                elem.className += (elem.className ? ' ' : '') + className;
            }
        };
        removeClass = function (elem, className) {
            if (hasClass(elem, className)) {
                elem.className = elem.className.replace(new RegExp('(^|\\s)*' + className + '(\\s|$)*', 'g'), '');
            }
        };
        toggleClass = function (elem, className) {
            (hasClass(elem, className) ? removeClass : addClass)(elem, className);
        };
    }
    
    apollo.hasClass = hasClass;
    apollo.addClass = addClass;
    apollo.removeClass = removeClass;
    apollo.toggleClass = toggleClass;
    
    window.apollo = apollo;
    
})();

apollo.addClass(document.body, 'test');