Jon Weatherhead

AJAX Comments Refueled allows for pages to be cached without needing to invalidate on new comments, and is useful for upgrading the default comment system to not rely on page refreshes for replying to comments.
This plugin is a zero-dependency implementation. This means that it does not require jQuery.
Image by <a href="https://pixabay.com/users/geralt-9301/?utm_source=link-attribution" rel="nofollow ugc">Gerd Altmann</a> from Pixabay.
<h3>How To Use</h3>
Simply install and activate this plugin and it will work – there are no options to fuss over.

AJAX Comments Refueled

An all-AJAX drop-in for the stock comments system.

Mark Jaquith

Michael Adams (mdawaffe)

Other preview plugins don’t know what sort of changes WordPress will make to a 
visitor’s comment, but this plugin uses AJAX and other buzzwords to send each 
previewed comment through WordPress’ inner voodoo.
The result? With the click of a button, your site’s visitors can preview their 
comments exactly as they will appear when they submit them for realies.
Requires PHP5.

Ajax Comment Preview

Visitors to your site can preview their comments with a click of a button.

AJAX Comments Refueled vs Ajax Comment Preview