POST form with JQuery using $.post()

I have the following form

<script type="text/javascript">
<input type="text" id='responseText' name="responseText" value="">
<input type="button" id='confirm' name="confirm" value="confirm">
<input type='text' id="idNum" name="idNum">
<input type='text' id='correct' id="correct">
</form>

Only the value for #responseText is actually typed in, #idNum is passed from another page, while the other fields are filled by this function:

<script type="text/javascript">
var arr = [2,5,6,7,10,16,29,42,57];
x = 0
/* idNum is passed from another page to this one */
$(document).ready(function() {
    document.getElementById('idNum').value = localStorage.memberID;
    /* when something is typed in the form */
    $('#responseText').on('input', function() {
        /* the value is stored */
    var response = document.getElementById('responseText').value;
    /* and compared with the vector arr that contains the correct answers*/
    if( response == arr[x]){
        $("#correct").attr('value', 'yes');
    }
    else{ 
        $("#correct").attr('value', 'no');
        };
    });
/* confirm is the button to send the asnwer */
$('#confirm').click(function(){
    x = x + 1;
});
}); 

</script>

And here is my php:

<?php
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$response = $_POST["responseText"];
$memberID = $_POST["idNum"];
$timeStmp = time();
$correct = $_POST["correct"];

$sql = "INSERT INTO colorBlind (memberID, response, correct, timeStmp)
VALUES ('$memberID', '$response' ,'".$correct."','".$timeStmp."')";

if ($conn->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn -> close();

?>

Now, I am sure the php is called correctly when the click event occurs on #confirm, because the timestamp invoked in the php is recorded in my db. Nevertheless, none of the value in the fields is passed in the php. Namely if do somethin like:

echo $_POST["idNum"];

I get back an empty field.

Anybody has any idea what I am doing wrong or any suggestions on how to debug it? I have been spending days on this without any progress.