JavaScript, Add, remove, and toggle a class name in a given DOM element with pure JavaScript

classes.js

define(function() {
    return {
        /**
         * Adds a class name to an element
         * @param {element} el The target element
         * @param {string}  clazz The class names wanted to add
         */
        add: function addClass(el, clazz) {
            var cn = el.className;
            // Test for existance
            if (cn.indexOf(clazz) != -1) {
                return;
            }
            // Add a space if the element already has class
            if (cn != '') {
                clazz = ' ' + clazz;
            }
            el.className = cn + clazz;
        },

        /**
         * Remove class from a given element
         * @param {element} el    The targetend element
         * @param {class}   clazz The class name to remove
         */
        remove: function(el, clazz) {
            el.className = el.className.replace(new RegExp('(?:^|\\s)' + clazz + '(?!\\S)'), '');
        },

        /**
         * Toggles class in element
         * @param {element} el    Reference to an element
         * @param {string}  clazz The class name to toggle
         */
        toggle: function(el, clazz) {
            var cn = el.className;
            if (cn.indexOf(clazz) != -1) {
                this.remove(el, clazz);
            } else {
                this.add(el, clazz);
            }
        }
    }
});