<div class="habr--one habr--two habr--three keep--it">
  QnA
</div>

.habr--one { font-weight: bold }
.habr--two { color: red }
.habr--three { text-decoration: underline }
.keep--it { padding: 2em; margin: 2em; border: 3px dotted #AAA }

const removeClasses = (el, start) =>
  [...el.classList]
    .filter(className => className.startsWith(start))
    .forEach(className => el.classList.remove(className));

setTimeout(removeClasses, 3000, document.querySelector('div'), 'habr--');