JSFiddle - React, Tailwind, and code Playground

HTML

<input id="first"></input>
<br>
<input id="output" style="display:none"></input>
<br>
<input type='button' onclick='convertinput()' value='convert'>

JavaScript

function convertinput() {
    document.getElementById('output').value = "@@[0:1: " + document.getElementById('first').value + "]]";
   document.getElementById('output').style.display = 'block';
}