动态添加class

export function hasclass(el, classname) {
  let reg = new regexp('(^|\\s)' + classname + '(\\s|$)')
  return reg.test(el.classname)
}

export function addclass(el, classname) {
  if (hasclass(el, classname)) {
    return
  }

  let newclass = el.classname.split(' ')
  newclass.push(classname)
  el.classname = newclass.join(' ')
}

addclass(元素, 'item-类名')