show.html.erb

<!-- app/views/movies/show.html.erb -->

<div id="rating">Loading rating...</div>

<script>
  const checkRating = () => {
    fetch("<%= movie_rating_path(@movie) %>")
      .then(response => response.text())
      .then(response => {
        document.getElementById("rating").innerHTML = response;
      });
  };

  setInterval(checkRating, 2000);
</script>