a function to reload, refresh or update the div content (part of page, not whole page) when buttom clicked using javascript ajax without jquery?

this code is in function.php

<?php
# get company function
function get_company($db)
{
    $company_id = $_GET['id'];
    $company = $db->prepare("SELECT * FROM companies WHERE company_id = :company_id");
    $company->execute(['company_id' => $company_id]);
    $company = $company->fetch();
    return $company;
}
?>

this code is in index.php (the main file or home page)

<?php
$companies = get_companies($db);
?>
<article id="article">
            <?php if ($companies->rowCount() > 0) { ?>
                <!-- list of all companies -->
                <?php 
                foreach ($companies as $company) {
                ?>
                    <a class="i" href="2.php?id=<?= $company['company_id'] ?>">
                        <div class="h">
                            <img src="images/<?= $company['company_image'] ?>">
                        </div>
                        <h2><?= $company['company_name'] ?></h2>
                    </a>
                <?php } ?>
            <?php } else { ?>
                <div class="n">empty</div>
            <?php }  ?>
</article>

<button id="button1" onclick="m(this.id)">click me to reload articles</button>
<button id="button2" onclick="m(this.id)">click me to reload articles</button>
<button id="button3" onclick="m(this.id)">click me to reload articles</button>

this code is in js file

<script>
function article(id) {
  url = new URL(window.location.href);
  url.searchParams.set("group_id", id);
  window.history.pushState("", "", url);

  xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function () {
    if (this.readyState == 4 && this.status == 200) {
      document.getElementById("article")...//write some code here to refresh or reload article element when you click button.
    }
  };
  url.search;
  xhttp.open("GET", "php/function.php"+url, true);
  xhttp.send();
}
</script>

I don’t know how can I reload, refresh or update the div content (part of page, not whole page) when buttom clicked using javascript ajax.

I need a function to get url content and reload the article div (not whole page, part of a page) something like ajax using java script but not jquery or other libraries.