How to Add or Change Class Name by Javascript - BD WebTeach

<style> .dark{background:black;color:white;} </style> <button id="button">Dark</button> <div id="body" class="body">hellow world</div> <script> var body = document.getElementById("body"); var button = document.getElementById("button"); button.onclick = function() { if(body.className == "dark") { body.className = "body"; button.innerHTML = "Dark"; } else{ body.className = "dark"; button.innerHTML = "Light"; } }; </script>