JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <button name="btnK">Button</button>
</div>

CSS

.my-button {
  padding: 20px;
  background: crimson;
  color: #fff;
}

JavaScript

var x = document.getElementsByName("btnK"),
	parent,
  button;

if (x && x.length) {
    parent = x[0].parentNode;
    
    button = document.createElement("button");
    button.id = 'my-new-button';
    button.textContent = 'Click me';
    button.classList.add('my-button');
    button.addEventListener('click', function() {
    	alert('clickie');
    });
    
    parent.appendChild(button);
}