CodePen Embed - XWWvEMZ

<div class="test">3</div>
<div class="test">7</div>
<div class="test">10</div>
<div class="test">23</div>

const tests = document.querySelectorAll('.test');
tests.forEach(item => {
  if (Number(item.textContent) < 10) {
    item.classList.add('active')
  }
})

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