Creation Methods

<!DOCTYPE html>
<html>
<head>
<style>
.democlass {
  color: blue;
}
</style>
</head>
<body>

<h1>CloseTag</h1>

 
<button onclick="myFunction()">Try it</button>

<script>
function myFunction() {
  var h1 = document.getElementsByTagName("H1")[0];
  var att = document.createAttribute("class");
  att.value = "democlass";
  h1.setAttributeNode(att);
}
</script>

</body>
</html>