Ajax, retrieving ID of insert from within function - php

Question

I'm trying to use Ajax to insert form data into the database and return the ID of that insertion.
It currently works as far as inserting (I can see it in the database) but I'm using alert to test that it's getting the ID of the insert and it simply says undefined.
Is there something I'm doing wrong to retrieve the ID?
<script type="text/javascript">
$(document).ready(function(){
$("#submitForm").click(function(){
var string = $('#pageForm').serialize();
// AJAX Code To Submit Form.
$.ajax({
type: "POST",
url: "addPage.php",
data: string,
cache: false,
success: function(result){
alert(result.id);//this will alert you the last_id
}
});
});
});
</script>
addPage.php
$title = $_POST['addTitle'];
$page_type = $_POST['pageType'];
$display_id = $_POST['displayId'];
$duration = $_POST['durationSet'];
$addpage = "
INSERT INTO pages (title, page_type_id, display_id, duration)
VALUES ('$title','$page_type','$display_id','$duration');
";
if ($mysqlConn->query($addpage) === TRUE) {
$last_id = $mysqlConn->insert_id;
echo json_encode(['id'=>$last_id]);
echo "New record created successfully" . $last_id;
} else {
echo "Error: " . $addpage . "<br>" . $mysqlConn->error;
}

Answer 1

Try to return last inserted data id
$title = $_POST['addTitle'];
$page_type = $_POST['pageType'];
$display_id = $_POST['displayId'];
$duration = $_POST['durationSet'];
$addpage = "
INSERT INTO pages (title, page_type_id, display_id, duration)
VALUES ('$title','$page_type','$display_id','$duration');
";
if ($mysqlConn->query($addpage) === TRUE) {
$last_id = $mysqlConn->insert_id;
$data = json_encode(['id'=>$last_id]);
echo "New record created successfully" . $data ;
} else {
echo "Error: " . $addpage . "<br>" . $mysqlConn->error;
}

Answer 2

https://www.w3schools.com/PHP/php_mysql_insert_lastid.asp
Please first search before ask a question
if ($mysqlConn->query($addpage) === TRUE) {
$last_id = $mysqlConn->insert_id;
echo "New record created successfully" . $last_id;
} else {
echo "Error: " . $addpage . "<br>" . $mysqlConn->error;
}