<meta charset="UTF-8">
<script>
{
    let fm =
        {
            timeZone: 'Asia/Tokyo',
            era: 'long',
            year: 'numeric',
            month: 'long',
            day: 'numeric',
            hour: 'numeric',
            minute: 'numeric',
            second: 'numeric',
            weekday: 'long',
            timeZoneName: 'long'
        },
        tn;
    function Proc ()
    {
        let d = new Date();
        setTimeout(Proc, 1001 - d.getMilliseconds());
        tn.nodeValue = d.toLocaleString('ja-JP-u-ca-japanese', fm);
    }
    document.addEventListener('DOMContentLoaded', ()=>
    {
        tn = document.getElementById('Output').appendChild(document.createTextNode(''));
        Proc();
    });
}
</script>
<div id="Output"></div>