Passing array values in PHP using ajax

See more:

PHP

Ajax

jQuery

I have this code which insert book details , but im currently having a problem in passing array values to my ajax function. I'm kinda new to ajax so im still getting the hang of it .

MY HTML INPUT TEXTBOX

 <input type="text" class="form-control text-center" id="author_lname[]" name="author_lname[]" placeholder="Last Name" required>
<input type="text" class="form-control text-center" placeholder="First Name" id="author_fname[]" name="author_fname[]" required>
<input type="text" class="form-control text-center" id="author_mname[]" name="author_mname[]" placeholder="Middle Name / Initial" required>

MY AJAX FUNCTON

var getauthor_lname = $("#author_lname").val();
     var getauthor_fname = $("#author_fname").val();
     var getauthor_mname = $("#author_mname").val();
     var whatprocess = "ADDBOOK";
 $.ajax({
        url: "adminfunctions.php",
        method: "POST",
       data: {getauthor_lname:getauthor_lname, 
              getauthor_fname:getauthor_fname,
              getauthor_mname:getauthor_mname , 
              whatprocess : whatprocess
        },
        success: function(data) {
               var getdata = data.trim();
               if (getdata == "SUCCESS") {
                swal({
                      title: 'Success!',
                      text: '',
                      type: 'success',
                      confirmButtonClass: "btn btn-success",
                      buttonsStyling: false
                    }).then(function() {
                      $("#datatables").load(window.location + " #datatables");
                                  });
                                }
                                else {
                                    swal({
                                        title: 'Sorry for the inconvenience!',
                                        text: "There's a problem. Please contact the technical support for any concerns and questions.!",
                                        type: 'error',
                                        confirmButtonClass: "btn btn-danger",
                                        buttonsStyling: false
                                    }).catch(swal.noop)
                                }
                            },
                            error: function(jqXHR, exception) {
                                console.log(jqXHR);
                            }
                        });

AND MY PHP FOR INSERTING DATA

$getauthor_lname = $_POST["getauthor_lname"];
$getauthor_fname = $_POST["getauthor_fname"];
$getauthor_mname = $_POST["getauthor_mname"];

for ($i = 0; $i < count($getauthor_fname); $i++) {
        if ($getauthor_fname[$i] != "" && $getauthor_mname[$i] != "" && $getauthor_lname[$i] != "") {
            $query = "INSERT INTO tbl_author (book_isbn, author_firstname, author_middlename, author_lastname) VALUES (? , ? , ? , ?)";
            $stmt = $mysqlconnection->prepare($query);
            $getauthor_lname[$i] = htmlspecialchars(strip_tags($getauthor_lname[$i]));
            $getauthor_fname[$i] = htmlspecialchars(strip_tags($getauthor_fname[$i]));
            $getauthor_mname[$i] = htmlspecialchars(strip_tags($getauthor_mname[$i]));
            $stmt->bind_param("ssss", $getbook_isbn, $getauthor_fname[$i], $getauthor_mname[$i], $getauthor_lname[$i]);
            $stmt->execute();
        }else{

            echo "ERRORauthor";
        }
    }

What I have tried:

I havent tried anything yet , but any help would be great !