The sup() method of String values creates a string that embeds this string in a 
 element (<sup>str</sup>), which causes this string to be displayed as superscript.
Note: All HTML wrapper methods are deprecated and only standardized for compatibility purposes. Use DOM APIs such as
document.createElement()instead.
Syntax
sup()
Parameters
None.
Return value
A string beginning with a <sup> start tag, then the text str, and then a </sup> end tag.
Examples
Using sup()
The code below creates an HTML string and then replaces the document's body with it:
const contentString = "Hello, world";
document.body.innerHTML = contentString.sup();
This will create the following HTML:
<sup>Hello, world</sup>
Instead of using sup() and creating HTML text directly, you should use DOM APIs such as document.createElement(). For example:
const contentString = "Hello, world";
const elem = document.createElement("sup");
elem.innerText = contentString;
document.body.appendChild(elem);