はてなブログに今日が第何週目かを表示するやつ

week_counter.html

<p>
今週は<span id="izumi-year"></span>年の第<span id="izumi-week-counter"></span>週目です🐠<br/>
<small>(全<span id="izumi-week-max"></span>週)</small>
</p>

week_counter_footer.html

<script src="https://cdnjs.cloudflare.com/ajax/libs/dayjs/1.10.7/dayjs.min.js" integrity="sha512-bwD3VD/j6ypSSnyjuaURidZksoVx3L1RPvTkleC48SbHCZsemT3VKMD39KknPnH728LLXVMTisESIBOAb5/W0Q==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/dayjs/1.10.7/plugin/isoWeek.min.js" integrity="sha512-DtF47LXpLugOKYRow/LzzrgsoDgV28NfvTffF/lrVjECYgogCen79Kc5k30HaJJ9JriUiZB7Eh6Q7g+9PHhKzQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
<script>
    dayjs.extend(window.dayjs_plugin_isoWeek)
    const now  = dayjs();
    const end_of_year = now.endOf('year');
    document.getElementById("izumi-year").innerHTML=now.year();
    document.getElementById("izumi-week-counter").innerHTML=now.isoWeek();
    document.getElementById("izumi-week-max").innerHTML=end_of_year.isoWeek();
</script>