JSFiddle - React, Tailwind, and code Playground

HTML

<div class="comments_list">
    <div class="comment_item">
        <div class="comment_body">test1 - comments</div>
        <input type="button" class="hidereplies" value="show replies" />
        <div class="reply_comments">
            <div class="comment_body">want to hide only current ".reply_comments"</div>
        </div>
    </div>
    <div class="comment_item">
        <div class="comment_body">test2 - comments</div>
        <input type="button" class="hidereplies" value="show replies" />
        <div class="reply_comments">
            <div class="comment_body">but not all</div>
        </div>
    </div>
    <div class="comment_item">
        <div class="comment_body">test3 - no comments</div>
        <div class="reply_comments"></div>
    </div>
</div>

CSS

.comment_item {
border: 1px solid #dadada;
    margin-bottom: 5px;
}

JavaScript

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.querySelectorAll(".reply_comments");
        for (var y = 0; y < comments.length; y++) {
            var reply = comments[y];
            reply.style.display = (reply.style.display != 'none' ? 'none' : 'block');
        }
    };
}