JSFiddle - React, Tailwind, and code Playground
HTML
<pre id="output"></pre>
JavaScript
$('#output').append('foobar'.replace(/(?=(bar))/, '[$1]') + "\n");
$('#output').append('foobar'.replace(/(?=(bar))?/, '[$1]') + "\n");
$('#output').append('foobar'.replace(/(?:(?=(bar)))?/, '[$1]') + "\n");