js - class 操作

// 添加
function addClass(dom, classNameString = '') {
  if (!dom.className.length) dom.className = classNameString
  else if (dom.className.indexOf(classNameString) == -1) dom.className += ' ' + classNameString
}
// 移除
function removeClass(dom, classNameString = '') {
  if (dom.className.length && dom.className.indexOf(classNameString) != -1) {
    dom.className = dom.className
      .split(' ')
      .filter(v => v != classNameString)
      .join(' ')
  }
}
// 查询
function hasClass(dom, classNameString = '') {
  return dom.className.indexOf(classNameString) == -1
}