JSFiddle - React, Tailwind, and code Playground

HTML

<button class="I button">I</button>
<button class="O button">O</button>

<input id="code" type="text" disabled />

JavaScript

$('.button').click(function(event) {
    var text = $(this).text();
    $('input:text').val(function(index, val) {
        return val + text;
    });
});