Hinaloe

This plugin allow your site’s comment form makes ajax — non move/reload when user (including both subscriber, normal viewer, and admins too) post comment!
Most themes supports this plugin, but if your theme’s <code>class_form</code> have not <code>comment-form</code>, this plugin non supported.
And this plugin only can use for Pure WordPress Comment form. 
so, its not able to be used with like Jetpack comment form and other original/outside comment system/form.
Feature
<ul>
<li>post comment with ajax</li>
<li>Lite — this plugin only using a little of jQuery feature to modify DOM, and very tiny js & PHP code.</li>
</ul>
Require
You have to install <a href="https://wordpress.org/plugins/rest-api/" rel="ugc">WP REST API v2</a> to use this plugin if your site is running on WP 4.4-4.6.

ajax Post Comment

Post comment form on frontend tobe ajax using WP REST API Version.2

Ruhul Amin

Now you have no need to make additional requests to get author info from their id that is available in the default json response. 
This plugin allows you to configure which user meta fields should be included in the REST API response through an easy-to-use admin interface.
<h4>Features</h4>
<ul>
<li>Configurable user meta fields</li>
<li>Includes avatar URL option</li>
<li>Shows user role information</li>
<li>No additional API requests needed</li>
<li>Clean implementation</li>
</ul>
<h4>Available Fields</h4>
<ul>
<li>Nickname</li>
<li>Description</li>
<li>User URL</li>
<li>First Name</li>
<li>Last Name</li>
<li>User Email</li>
<li>Role</li>
<li>Avatar</li>
</ul>
Example Response: 
 { 
 “id”: 1, 
 “title”: “Sample Post”, 
 “author”: 1, 
 “author_meta”: { 
 “first_name”: “John”, 
 “last_name”: “Doe”, 
 “role”: “administrator”, 
 “avatar”: “https://secure.gravatar.com/…” 
 } 
 }
<h4>Credits</h4>
This plugin is created by <a href="https://www.linkedin.com/in/arruhulamin/" title="Ruhul Amin" rel="friend nofollow ugc">Ruhul Amin</a>
<h3>Support</h3>
For support, please visit http://www.ruhulamin.me/

WP REST API – User Meta

Just installed, activated this plugin and use it without any other configuration

Easy to use.

I used it for on of my projects and happy with it. Helped me what I needed.

Good Plugin

Enhance WordPress REST API by including configurable user meta fields in post responses without additional API requests.

ajax Post Comment vs WP REST API – User Meta