if (el.classList) {
    el.classList.toggle(className)
} else {
    var classes = el.className.split(' ')
    var existingIndex = -1
    for (var i=classes.length; i--;){
      if (classes[i] === className)
        existingIndex = i;
    }

    if (existingIndex >= 0)
      classes.splice(existingIndex, 1)
    else
      classes.push(className);

    el.className = classes.join(' ')
}
