JSFiddle - React, Tailwind, and code Playground

HTML

<h1>My Web Page</h1>

<p id="demo">A Paragraph</p>

<button type="button" id='btn1'>Try it</button>

JavaScript

var btn = document.getElementsByTagName('btn1');
console.log(btn);
alert(btn);

$('#btn1').click=(function(){
    alert('entered');
document.getElementById("demo").innerHTML="test";
});