how to add html heading using javascript code example

Example 1: h1 tag html

<h1> heading 1</h1>

Example 2: html headings

<h1>I'm the biggest heading</h1>
<h2>I'm smaller than h1</h2>
<h3>I'm smaller than h2</h3>
<h4>I'm smaller than h3</h4>
<h5>I'm smaller than h4</h5>
<h6>I'm the smallest heading</h6>