I will show you piece of solution that I use in my project. I cannot say it is optimal or best practices, but it works for me and can work for you:
PHP:
function doLoadMails(){
//initialize empty variable
$mails;
$conn = new mysqli($_POST['ip'], $_POST['login'], $_POST['pass'], $_POST['db']);
// Check connection
if ($conn->connect_error) {
die("");
}
//some select, insert, whatever
$sql = "SELECT ... ... ... ";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
// output data of each row, j is counter for rows
$j =0;
while($row_a = $result->fetch_assoc()) {
//for each row, fill array
$mails[$j][0] = $row_a["name"] ;
$mails[$j][1] = $row_a["mail"] ;
$mails[$j][2] = $row_a["language"] ;
$j++;
}
}
//if $mails has results (we added something into it)
if(isset($mails)){
echo json_encode($mails);/return json*/ }
else{
//some error message you can handle in JS
echo"[null]";}
}
and then in JS
function doLoadMails() {
$.ajax({
data: { /*pass parameters*/ },
type: "post",
url: "dataFunnel.php",
success: function(data) { /*data is a dummy variable for everything your PHP echoes/returns*/
console.log(data); //you can check what you get
if (data != "[null]") { /*some error handling ..., in my case if it matches what I have declared as error state in PHP - !(isset($mails))*/ }
}
});
Keep in mind, that you can echo/return directly the result of your SQL request and put it into JS in some more raw format, and handle further processing here.
In your solution, you will probably need to echo the return code of the INSERT request.