JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<label class="selectit"><input value="84" name="download_category[]" id="in-download_category-84" type="checkbox"> CPU, HDD, Ram</label>

<button  id='checkit'>Check</button>

JavaScript

$(document).ready(function () {
                $('#checkit').click(function () {
                    if ($(input[type="checkbox"]).prop("checked") == true) {
                        alert("Checkbox is checked.");
                    } else {
                        alert("Checkbox is unchecked.");
                    }
                });
            });