JSFiddle - React, Tailwind, and code Playground

HTML

<div class="comments_list " id="comments">

  <h2 class="title ">комментарии (<span id="comments_count">53</span>)
  
  </h2>

    <div class="comment_item" id="comment_6538622">
	
	<span class="parent_id" data-parent_id="0"></span>
	<div class="comment_body">
			<div class="info " rel="6538622">
				<div class="folding-dot-holder"><div class="folding-dot"></div></div>
				<div id="voting_6538622" class="voting   ">
						<span class="minus" title="Голосовать могут только зарегистрированные пользователи"></span>
						<span class="plus" title="Голосовать могут только зарегистрированные пользователи"></span>
					<div class="mark positive ">
							<span class="score" title="Всего 6: ↑6 и ↓0">+6</span> 
					</div>	 
				</div>
				<a href="http://habrahabr.ru/users/Maximus43/" class="avatar"><img src="http://media.habrahabr.ru/images/thumbs/avatars/1d/d5/52/34272/small_34272.jpg" alt=""></a>
				<a href="http://habrahabr.ru/users/Maximus43/" class="username">Maximus43</a><span class="comma">,</span>
				<time>29 июля 2013 в 12:16</time>
				
				<a href="#comment_6538622" class="link_to_comment">#</a>
				<span class="to_chidren"></span>
				<div class="clear"></div>
			</div>
			<div class="message html_format ">
				Тема SNI не раскрыта 
			</div>
			<div class="reply_form_placeholder"></div>
			<div class="reply">
				
			</div>
	</div>
	
	<div class="reply_comments" id="reply_comments_6538622">
		<div class="comment_item" id="comment_6538644">
	
	<span class="parent_id" data-parent_id="6538622"></span>
	<div class="comment_body">
			<div class="info " rel="6538644">
				<div class="folding-dot-holder"><div class="folding-dot"></div></div>
				<div id="voting_6538644" class="voting   ">
						<span class="minus" title="Голосовать могут только зарегистрированные пользователи"></span>
						<span class="plus" title="Голосовать могут только зарегистрированные пользователи"></span>
					<div class="mark  ">
							<span class="score" title="Всего 0: ↑0 и...

JavaScript

hideReplies ();
  
  function hideReplies () {
  
function getChildrenByClassName(el, className) {
    var children = [];
    for (var i = 0; i < el.childNodes.length; i++) {
        if (el.childNodes[i].className == className) {
            children.push(el.childNodes[i]);
        }
    }
    return children;
}

function addBtn() {
    var comments = document.querySelectorAll(".comments_list > .comment_item"),
        comment, combody;

    for (var i = 0; i < comments.length; i++) {
        comment = comments[i];
        var replies = comment.querySelectorAll('.reply_comments .comment_body');
        if (replies.length > 0) {
            combody = getChildrenByClassName(comment, 'comment_body')[0];
            if (combody) {
                var btn = document.createElement("input");
                btn.type = "button";
                btn.className = "hidereplies";
                btn.value = "show replies";
                combody.appendChild(btn); //don't show if replies.childNodes.length === 1
            }
        }
    }
}
addBtn();


function hideR() {
var buttons = document.querySelectorAll(".hidereplies");

for (a = 0; a < buttons.length; a++) {
    var btn = buttons[a];
    btn.onclick = function (event) {
        var btn = event.currentTarget;
        var comments = btn.parentNode.parentNode.querySelectorAll(".reply_comments");
        for (var y = 0; y < comments.length; y++) {
            var reply = comments[y];
            reply.style.display = (reply.style.display != 'none' ? 'none' : 'block');
        }
    };
}
}
hideR();

    
}