JSFiddle - React, Tailwind, and code Playground

JavaScript

function hasClass(el, className) {
    var fullClass = el.hasAttribute('class') ? el.getAttribute('class') : false;
    if (!fullClass) return false;
    if (fullClass.indexOf(className) == -1) return false;
    if (fullClass.length == className.length) return true;
    if (fullClass.indexOf(className) == 0) {
        if(fullClass.charAt(className.length) !== ' ') return false;
        return true;
    }
    if (fullClass.indexOf(className) + className.length === fullClass.length) {
        if (fullClass.charAt(fullClass.length - className.length - 1) !== ' ') return false;
        return true;
    }
    if (fullClass.charAt(fullClass.indexOf(className) - 1) !== ' '
        || fullClass.charAt(fullClass.indexOf(className) + className.length)) !== ' ')
        return false;
    return true;
}