Untitled

<!DOCTYPE HTML>
<html>
<head>
    <meta charset="utf-8">
    <title>length</title>
</head>
<body>
<p id="elem" class="www ggg zzz"></p>
<script>
    let elem = document.querySelector('#elem');
    let classNames = elem.classList;

    for (let className of classNames) {
        document.write(className + '<br>');
    }
</script>
</body>
</html>