davej

const transitionToPromise = (el, property, value) =>
  new Promise(resolve => {
    el.style[property] = value;
    const transitionEnded = e => {
      if (e.propertyName !== property) return;
      el.removeEventListener('transitionend', transitionEnded);
      resolve();
    }
    el.addEventListener('transitionend', transitionEnded);
  });