How do I response partial html with fetch

I response posts in partials html with fetch, but each time get posts from server also return current page header. i just want to get header first.

partial html(server responses it when requested with fetch)

{% for post in posts %}
    <div class="posts-item">
        {{post.description|linebreaks|truncatewords:20}}
        Published at {{post.created}} by {{post.author}}
        <br>
        {% for tag in post.tag.all %}
            <a href="{% url 'social:post_list_by_tag' tag.slug %}">{{tag.name}}</a>
            {% if forloop.last %}, {% endif %}
        {% endfor %}
        <a href="{% url 'social:post_detail' post.pk %}">post details</a>
        <hr><br>
    </div>
{% endfor %}

current page(posts-list.html)

{% extends 'parent/base.html' %}
{% block title%} posts list {% endblock %}
{% block content %}

<div class="posts">
    {% for post in posts %}
        {{post.description|linebreaks|truncatewords:20}}
        Published at {{post.created}} by {{post.author}}
        <br>
        {% for tag in post.tag.all %}
            <a href="{% url 'social:post_list_by_tag' tag.slug %}">{{tag.name}}</a>
            {% if forloop.last %}, {% endif %}
        {% endfor %}
        <a href="{% url 'social:post_detail' post.pk %}">post details</a>
        <hr><br>
    {% endfor %}
</div>

<button class="load-more">load more</button>
<script>
    var page = 2;
    function loadMore(){
        var url = '{% if tag_slug %}{% url "post_list_by_tag" tag.slug %}{% else %}{% url "social:post_list" %}{% endif %}'+'?page='+page;
        fetch(url, {
            method: 'GET',
            headers: {
                'content-type': 'text/html', 'x-requested-with': 'XMLHttpRequest'
            },
        }).then(function(response){
            return response.text();
        }).then(function(html){
            document.querySelector(".post").insertAdjacentHTML("beforeend",html);
            page++;
        })
    }
    var btnLoadMore = document.querySelector(".load-more");
    btnLoadMore.addEventListener("click", loadMore);
</script>
{% endblock %}

}).then(function(html){
    const parser = new DOMParser();
    const parsedHTML = parser.parseFromString(html,"text/html");
    const targetHTML = parsedHTML.querySelector("yourSelectorHere");
    document.querySelector(".post").insertAdjacentHTML("beforeend",targetHTML);
    ...
})