unicorn-utterances/content/blog/what-is-reactivity/step1-code/index.html

<main>
  <button id="add-button">Count: 0</button>
</main>
<script>
  let count = 0;

  const addBtn = document.querySelector('#add-button');
  addBtn.addEventListener('click', () => {
    count++;
    addBtn.innerText = `Count: ${count}`;
  });
</script>