JSFiddle - React, Tailwind, and code Playground

HTML

<input id="1" type="checkbox" />
<input id="2" type="checkbox" checked="checked" />
<input type="checkbox" />
<input id="4" type="checkbox" checked="checked" />
<input type="checkbox" />

JavaScript

var selected = new Array();
$('input:checked').each(function() {
    selected.push($(this).attr('id'));
});

console.log(selected);