No thrown visible errors when mysqli_query has incorrect values (using AJAX)

Question

I have 1 file whichs uses PhP, JavaScript, HTML, AJAX, CSS, MySQLi and SQL that is basically a page with some fields and then it sends the information to a database using AJAX to do the connection without refreshing the page.

Everything is working except that I can't make it show errors with the or die(). I tested it out by changing one of the values in the my_table(...) which makes it not send information to the database but the user has no ideia because there's no error message. How can I make it throw errors?

I have no ideia what I'm doing wrong but if I had to bet it would be the AJAX not refreshing the page or something. I have seen some questions out there which I'm sure they explain exactly this but the jQuery confuses me all the time.

Here's my code with some modifications to reduce the non-important stuff:

<?php
  if(isset($_POST["name"]) && !empty($_POST["name"])) {
    $link = mysqli_connect("127.0.0.1", "my_user", "my_password", "my_db");
    mysqli_set_charset($link, "utf8");
    // code
    mysqli_query($link, "INSERT INTO my_table(...)values(...)") or die(mysqli_error($link));
    mysqli_close($link);
    exit;
  }
?>
<html>
  <head>
    <meta charset="UTF-8">
    <script>
      function AJAX() {
        // code
        var xhttp = new XMLHttpRequest();
        xhttp.open('POST', 'my_file.php', true);
        xhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
        xhttp.send(...);
      }
    </script>
  </head>
  </body>
    <!-- code -->
    <button onclick="AJAX()">Send</button>
  </body>
</html>

Edit to explain better the situation:

If I use this simple code it works fine:

<?php
$link = mysqli_connect("127.0.0.1", "my_user", "my_password", "my_db");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}
mysqli_query($link,"INSERT INTO my_table(Name) VALUES ('Bob')") or die(mysqli_error($link));
mysqli_close($link);
?>

But, for example, when I change my_table to a wrong name which doesn't exist it writes in the document Table 'my_db.wrong_table_name' doesn't exist. While in my file it doesn't write/show/throw nothing at all and it makes the user think it worked when it didn't.

If you want to refresh the page do not use AJAX. Similarly, using AJAX to ping code in the same page is a time-bender of a mistake. And, there is no jQuery here. — Jay Blanchard, Mar 17 '17 at 16:06
That's actually an awful idea. [mysqli or die, does it have to die?](http://stackoverflow.com/questions/15318368/mysqli-or-die-does-it-have-to-die) — Your Common Sense, Mar 17 '17 at 16:16
[You are not the only user of your site.](https://phpdelusions.net/programming) — Your Common Sense, Mar 17 '17 at 16:17

score 0 · Answer 1 · edited May 23 '17 at 12:00

This should alert an error:

        var xhttp = new XMLHttpRequest();
        xhttp.addEventListener("error", function(event) {
            alert('an error occured');
        });
        xhttp.open('POST', 'my_file.php', true);
        xhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
        xhttp.send(...);

You can find all informations about eventListener here: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest

Keep in mind, that this error-event is only fired on network-failure. If you need to handle different http-codes, you will find a good example here: XMLHttpRequest (Ajax) Error

did you read this? http://stackoverflow.com/questions/8866761/xmlhttprequest-ajax-error — Oliver, Mar 18 '17 at 08:49

No thrown visible errors when mysqli_query has incorrect values (using AJAX)

1 Answers1