js代碼：
let?box?=document.querySelector('.box')
????console.log(box)
????box.onclick?=?function(){
????????switchClass(this,"active")
????}
????function?switchClass(obj,?sClass)?{
?????????var?oldClass?=?obj.className;
?????????var?re?=?new?RegExp('\\b'?+?sClass?+?'\\b');
?????????if?(re.test(oldClass))?{
?????????????obj.className?=?obj.className.split(sClass).join("").replace(/\s+$/,?"")
?????????}?else?{
?????????????obj.className?=?oldClass?+?"?"?+?sClass
?????????}
?????}
