JSFiddle - React, Tailwind, and code Playground

HTML

<p id="date"></p>

JavaScript

(function showTime() {
        setTimeout(function () {
            var d = new Date();
            
            document.getElementById('date').innerHTML = formatDate(d);
            
            showTime();
        }, 1000);
    })();

    function formatDate(date) {
        return [date.getFullYear(), date.getMonth() + 1, date.getDate()].join('-') + ':' +
            [date.getHours(), date.getMinutes(), date.getSeconds()].join(':');
    }

    function formatDatePart(part) {
        return part < 10 ? ("0" + part) : part;
    }