<body>
<button id="back"><</button>
<span id="date"></span>
<button id="forward">></button>
<script>
const msinday = 24*60*60*1000;
let curday = Date.now();
const sdate = document.getElementById('date')
const outdate = (date) => {
const opt= { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' };
const str = new Intl.DateTimeFormat('ru', opt).format(new Date(date))
sdate.textContent = str
}
document.getElementById('back')
.addEventListener('click', ()=> {curday -= msinday; outdate(curday)});
document.getElementById('forward')
.addEventListener('click', ()=> {curday += msinday; outdate(curday)});
outdate(curday);
</script>
</body>