Scroll loading using jquery and PHP

This article explains how to incrementally load items as you scroll down the page. In this example a HTML page is created with an unordered list element where the list items returned by the function gets appended.

HTML Page

<div>
  <ul id="containerName"></ul>
  <div style="text-align: center;"><img alt="Loading..." src="../assets/images/svg/three-dots.svg" class="loading-info" /></div>
  <div id="notifyMessage"></div>
</div>
Jquery
$(document).ready(function () {
  var offset = 0;
  var loading = false;
  $('.loading-info').hide();
  appendItems(offset, loading);
  $(window).scroll(function () {
        if ($('#notifyMessage').html() === "") {
            if ($(window).scrollTop() + $(window).height() >= $(document).height() - 100) {
                offset += 20;
                appendItems(offset, loading);
            }
        }
    });
});
function appendItems(offset, loading) {
    if (loading == false) {
        loading = true;
        $('.loading-info').show();
        $.post('/admin/items/append', { 'offset': offset }, function (data) {
            loading = false;
            if (data.trim().length == 0) {
                $('.loading-info').hide();
                $('#notifyMessage').html('<p> End of records</p>');
                return;
            }
            $('.loading-info').hide();
 
            $("#containerName").append(data);
        }).fail(function (xhr, ajaxOptions, thrownError) {
            alert(thrownError);
        })
    }
}
PHP Function
function append()
{
        $list = NULL;
        $offset = $_POST['offset'];
        $servername = "localhost";
        $username = "username";
        $password = "password";
        $dbname = "myDB";
 
        // Create connection
        $conn = new mysqli($servername, $username, $password, $dbname);
        // Check connection
        if ($conn->connect_error) {
            die("Connection failed: " . $conn->connect_error);
        }
 
        $sql = "SELECT id, firstname, lastname FROM employees limit $offset, 20";
        $result = $conn->query($sql);
 
        if ($result->num_rows > 0) {
            // output data of each row
            while($row = $result->fetch_assoc()) {
                $list +=  "<li>id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "</li>";
            }
        } 
        $conn->close();
 
        echo $list;
}