目地:element.style.樣式修改比較消耗性能，下面的方法通過修改類名避免此類情況 添加class ``` function addClass(element,class_name){ element.className+=" "+class_name; } ``` 檢測是否含有class ``` function hasClass(element,class_name){ //\b 單詞邊界 var reg = new RegExp("\\b"+class_name+"\\b"); return reg.test(element.className); } //測試 var banner = document.querySelector('.banner'); console.log(hasClass(banner,"banner")); ``` 刪除class ``` function removeClass(element,class_name){ //\b 單詞邊界 var reg = new RegExp("\\b"+class_name+"\\b"); element.className=element.className.replace(reg,""); } ``` 切換class ``` function toggleClass(element,class_name){ if(hasClass(element,class_name)){ removeClass(element,class_name); }else{ addClass(element,class_name); } } ```