To change the string to be displayed as a subscript using JavaScript, use the sub() method. This method causes a string to be displayed as a subscript as if it were in a <sub> tag.
Example
You can try to run the following code to change the string to be displayed as a subscript −
<html>
<head>
<title>JavaScript String sub() Method</title>
</head>
<body>
<script>
var str = new String("Demo Text");
document.write("This is subscript: "+str.sub());
</script>
</body>
</html>