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                <div id="imgArea">
  <img id="targetImg" src="" />
  <p id="imgInfo"></p>


                img {
  max-width: 300px;


                (async () => {
  // 要素を取得
  const targetImg = document.querySelector("#targetImg");
  const imgInfo =  document.querySelector("#imgInfo");
  // 画像データを非同期で取得
  const fetchImg = await fetchImage(targetImg.src);
  // 更新日時を取得
  const modified = getModified(fetchImg);
  // 更新日時を表示
  imgInfo.textContent = "更新日時:" + formatDate(modified)

// fetch(非同期)
async function fetchImage(target) {
  const response = await fetch(target);
  if (response.ok) {
    return response;
  } else {
      throw new Error('The data could not be read');

// 更新日取得
function getModified(target) {
  const headers = target.headers;
  let lastModified = "";
  // 更新日時を取得(GMT)
  for (var pair of headers.entries()) {
    if (pair[0] === "last-modified") {
      lastModified = pair[1];
  return lastModified;

// GMTを年月日分に変換
function formatDate(targetDate) {
  const modified = new Date(targetDate);
  const year = modified.getFullYear();
  const month = modified.getMonth() + 1;
  const date = modified.getDate();
  const hours = modified.getHours();
  const minutes = modified.getMinutes();
  return +year + "年" + month + "月" + date + "日" + hours + "時" + minutes + "分";