JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <p>Click to change day</p>
    <button type="button" name="btnPrev" onclick="next()"><</button>
    <button type="button" name="btnNext" onclick="prev()">></button>
    <p id="todayField"></p>
    <script>
    var date = new Date();
    var currentDay = date.getDay();
    var days = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"];
    document.getElementById("todayField").innerHTML = days[date.getDay()];
    

    function next() {


        currentDay++;
        document.getElementById("todayField").innerHTML = days[currentDay];

    }

    function prev() {
	


        currentDay = currentDay-1;
        	alert(date.getDay())
        document.getElementById("todayField").innerHTML = days[currentDay];

    }
    </script>
  </body>