Pure-javascript functions to add/remove CSS classes.

add-remove-has-class.js

// Adapted from https://stackoverflow.com/a/28344281/484108
// and https://jaketrent.com/post/addremove-classes-raw-javascript/

function hasClass(el, className) {
    return !!el.className.match(new RegExp('(\\s|^)' + className + '(\\s|$)'));
}

function addClass(el, className) {
    if (!hasClass(el, className)) el.className += ' ' + className;
}

function removeClass(el, className) {
    if (hasClass(el, className)) {
        var reg = new RegExp('(\\s|^)' + className + '(\\s|$)');
        el.className = el.className.replace(reg, ' ').trim();
    }
}