Data e Hora em tempo real com JavaScript

HTML:

<div id="clock">
    <div id="time"></div>
</div>

CSS:

#clock {
	width: 350px;
	background-color: rgba(0, 0, 0, 0.4);
	margin: 0 15px 20px;
	padding: 20px;
	border-radius: 10px;
	box-shadow: 0 10px 10px -5px rgba(0, 0, 0, 0.8);
	border: 1px solid #333;
	text-align: center;
}
#time {
	color: #eee;
	font-size: 2rem;
	font-family: monospace;
}

JavaScript:

function dateTime() {
    var element = document.getElementById('time');
    var time    = new Date();
    var day     = time.getDate().toString().padStart(2, '0');
    var months  = ['01', '02', '03', '04', '05', '06', '07', '08', '09', '10', '11', '12'];
    var month   = months[time.getMonth()];
    var year    = time.getFullYear();
    var hour    = time.getHours().toString().padStart(2, '0');
    var minute  = time.getMinutes().toString().padStart(2, '0');
    var second  = time.getSeconds().toString().padStart(2, '0');
    element.textContent = `${day}/${month}/${year} ${hour}:${minute}:${second}`;
}
setInterval(dateTime, 1000);
dateTime();

Resultado: