使用SQL数据进行Ajax调用

I call ajax at my action.php file to get one data from DB and load it dynamically.

$.ajax({
        url: 'ajax.php', 
        type: "POST",
        data: "localid="+ <?php echo $prelocal; ?>,
        dataType: 'json',
        success: function(response){
            console.log("repo: "+response);
        }
});  

My ajax.php is quite simple. I added if condition to check if I will call that file directly, and it is working

<?php 
$localid = $_POST['localid'];
if(empty($localid)) {
  $localid = 1;
}
$i = "SELECT `userid` FROM `table` WHERE `localid` = '{$localid}'";
$ri = $conn->query($i);
$v = $ri->fetch_assoc();
echo json_encode($v);
?>

Call ajax.php directly giving me response

{"userid":"4"}  

But at action.php I do not get any console.log response (why?). What I want to do, is to get only digit as value to input. May I ask for hint?

You need to change your javascript as following.

var local_id = <?php echo $prelocal; ?>;
$.ajax({
        url: 'ajax.php',
        dataType: 'json',
        type: 'POST',
        data: {localid:local_id},
        success: function(data) {
            console.log(data);
        },
        error: function(jqXHR, textStatus, errorThrown) {
            console.log(errorThrown);
        }
    });