js 動態新增class封裝(es6語法)

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-類名`)