JSFiddle - React, Tailwind, and code Playground

HTML

<form class='myform'>
  <div class='form-block'>
    <span class='line'>1</span>
    <button class='new-line'>New Line</button>
    <button class='new-nested'>New Nested Line</button>
    <input class='input' type='text' placeholder='Enter Value...'>
    <button class='new-input'>Add input</button>
  </div>
</form>

JavaScript

function NL(event){
event.preventDefault()
  var original = document.getElementsByClassName('form-block')[0];
  var clone=original.cloneNode(true);
  document.getElementsByTagName('form')[0].appendChild(clone);
}

document.getElementsByClassName('new-line')[0].addEventListener('click',NL);