averageRatingIMDB.js

// Paste this into your console on IMDB's episodes page for a TV show.
function waitForEpisodes() {
  return new Promise((resolve, reject) => {
    const callback = function (mutationsList, observer) {
      resolve(mutationsList);
      observer.disconnect();
    };

    const observer = new MutationObserver(callback);
    observer.observe(document.getElementById("episodes_content"), {
      attributes: true,
      childList: true,
    });
  });
}
async function avgRatingPerSeason() {
  const numOfSeasons = $("#bySeason").children().length;
  const id = $("#bySeason").attr("tconst");
  const ratings = {};
  for (let i = 1; i <= numOfSeasons; i++) {
    CS.Episodes.changeTo("/title/" + id + "/episodes/_ajax?season=" + i);
    await waitForEpisodes();
    ratings["Season " + i] = (
      [...(list = $(".ipl-rating-star.small > .ipl-rating-star__rating"))]
        .map((e) => e.textContent)
        .map(Number)
        .reduce((a, c) => a + c) / list.length
    ).toFixed(2);
  }
  console.table(ratings);
}
avgRatingPerSeason();