orbis-comment-editor.php

<?php
/*
Plugin Name: Orbis Comment Editor
Plugin URI: http://www.orbiswp.com/
Description: The Orbis Comment Editor plugin convert the comments textarea to a WordPress editor.

Version: 1.0.0
Requires at least: 3.5

Author: Pronamic
Author URI: http://www.pronamic.eu/

Text Domain: orbis-comment-editor
Domain Path: /languages/

License: Copyright (c) Pronamic

GitHub URI: https://github.com/pronamic/wp-orbis-comment-editor
*/

/**
 * Comment form field comment.
 *
 * @see https://github.com/WordPress/WordPress/blob/4.5.2/wp-includes/comment-template.php#L2295-L2302
 * @see https://github.com/WordPress/WordPress/blob/4.5.2/wp-includes/js/comment-reply.js
 * @see http://bechster.com/add-tinymce-visual-editor-comment-form-wordpress/
 * @see http://stackoverflow.com/questions/10095696/remove-tinymce-control-and-re-add
 * @see https://www.tinymce.com/docs/api/class/tinymce/#get
 * @param string $field
 * @return string
 */
function orbis_comment_form_field_comment( $field ) {
	ob_start();

	?>
	<script type="text/javascript">
		var fixCommentEditor = function() {
			var settings = tinymce.get( 'comment' ).settings;

			tinymce.remove( '#comment' );

			tinymce.init( settings );

			var editor = tinymce.get( 'comment' );

			editor.focus();

			editor.selection.select( editor.getBody(), true );
			editor.selection.collapse( false );
		};

		jQuery( function( $ ) {
			$( '.comment-reply-link' ).click( function( e ) {
				fixCommentEditor();

				$( '#cancel-comment-reply-link' ).one( 'click', fixCommentEditor );
			} );
		} );
	</script>
	<?php

	wp_editor( '', 'comment', array(
		'teeny'         => true,
		'textarea_rows' => '7',
	) );

	$field = ob_get_clean();

	return $field;
}

add_filter( 'comment_form_field_comment', 'orbis_comment_form_field_comment' );