code snippet for changing an element class name(s)

class-change.js

    addClass(el, clas, callback) {
        if (el) {
            const contains = el.classList.contains(clas);
            if (contains) {
              // dont add the class again
            } else {
                el.classList.add(clas);
            }

            if (typeof callback === 'function') {
                callback.call();
            }
        }
    }

    removeClass(el, clas, callback) {
        const contains = (el !== undefined) ? el.classList.contains(clas) : false;

        if (contains) {
            el.classList.remove(clas)
        }

        if (typeof callback === 'function') {
            callback.call();
        }

    }