Element.classList

<ul>

    <li>html</li>

    <li>css</li>

    <li id="active" class="important current">JavaScript</li>

</ul>

<script>

function loop(){

   for(var i=0; i<active.classList.length; i++){

       console.log(i, active.classList[i]);

   }

}

// 클래스를 추가

</script>

<input type="button" value="DOMTokenList" onclick="console.log(active.classList);" />

<input type="button" value="조회" onclick="loop();" />

<input type="button" value="추가" onclick="active.classList.add('marked');" />

<input type="button" value="제거" onclick="active.classList.remove('important');" />

<input type="button" value="토글" onclick="active.classList.toggle('current');" />