index.js

document.addEventListener('DOMContentLoaded', () => {
  let els = document.querySelectorAll('div[is]');
  do {
    swapDivs(els);
    els = document.querySelectorAll('div[is]');
  } while (els.length > 0);
});

const swapDivs = (els) => {
  console.log('Bye bye divs! 🎉');
  els.forEach(el => {
    try {
      const newEl = document.createElement(el.getAttribute('is'));
      [...el.attributes].forEach(at => 
        // avoid the endless loop of <div is="div"></div>
        !(at.name === 'is' && at.value === 'div')
        ? newEl.setAttribute(at.name, at.value)
        : void 0
      );
      newEl.innerHTML = el.innerHTML;
      el.replaceWith(newEl);
    } catch (error) {
      console.error(`Cannot convert element: ${el.outerHTML}`);
    }
  })
}