var element = document.getElementById('element');
element.classList.add('class-1');
element.classList.add('class-2', 'class-3');
element.classList.remove('class-3');function myFunction() {
var element = document.getElementById("myDIV");
element.classList.add("mystyle");
} var someElement= document.getElementById("myElement");
someElement.className += " newclass";//add "newclass" to element (space in front is important)<!DOCTYPE html>
<html>
<head>
<title>JavaScript to add class name</title>
<style>
.addCSS {
color: green;
font-size: 25px;
}
</style>
</head>
<body style="text-align:center;">
<h1 style="color:green;">
GeeksforGeeks
</h1>
<p id="p"> A Computer Science portal for Geeks. </p>
<button onclick="addClass()"> AddClass </button>
<!-- Script to add class name -->
<script>
function addClass() {
var v = document.getElementById("p");
v.className += "addCSS";
}
</script>
</body>
</html>