<div id="panels">
    <div id="left_panel">
        Zde budou uživatelé.
    </div>
    <div id="right_panel">
        B
    </div>
</div>
<script>
    $.ajax
    ({
        url: "./res/forum/api/list_users.php",
        success: function(result)
        {
            $("#left_panel").html(result);
        }
    });

    $("#left_panel").on("click", ".output", function(event)
    {
        $.ajax
        ({
            url: "./res/forum/api/user_info.php?username=" + event.target.innerHTML,
            success: function(result)
            {
                $("#right_panel").html(result);
            }
        });
    });
</script>