code: function addClasses (el, classStr) {
    if (typeof classStr !== 'string' || classStr.length === 0) {
      return
    }
    var classes = classStr.split(' ')
    for (var i = 0; i < classes.length; i++) {
      var className = classes[i]
      if (className.length) {
        el.classList.add(className)
      }
    }
  }
docs: Utility function to add space-delimited class strings to a DOM element's classList