javascript: add or remove class

classutils.js

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

function addClass(el, className) {
    'use strict';
    if (el.classList) {
        el.classList.add(className);
    } else if (!hasClass(el, className)) {
        el.className += " " + className;
    }
}

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

usage.js

var el = document.getElementById('peace')
addClass(el, 'be-still')
// or
removeClass(el, 'be-still')