I am trying to post data to the server, which is running MySQL. I am running the following code but the console doesn't show me any error. Could you please take a look and tell me if you see something wrong? Any help would be appreciated because I can't find similar guidelines around.
What I want my code to do is this:  I want the user, through the window.prompt, to give 4 values which will be stored in the variables: user_id, book_id, game_id, site_id. Then these 4 values must be stored in my database.
index.html
<html>
<head>
  <script src="https://code.jquery.com/jquery-3.3.1.min.js" integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=" crossorigin="anonymous"></script>
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
  <script>
    function save3() {
      $("#user_id").val(prompt("Give the UserId:"))
      $("#book_id").val(prompt("Give the BookId:"))
      $("#game_id").val(prompt("Give the GameId:"))
      $("#site_id").val(prompt("Give the SiteId:"))
    }
  </script>
</head>
<body>
  <p align="center">example</p>
  <table align="center" width="730">
    <tr>
      <td align="center">
        <div>
          <table class="blueTable" style="float: left">
            <thead>
              <tr>
                <th colspan="1"><u>Menu</u></th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td><input type="button" value="New" id="new" onclick="new1()" class="button12" /></td>
              </tr>
              <tr>
                <td><input type="button" value="Load" id="load" onclick="load2()" class="button12" /></td>
              </tr>
              <tr>
                <td>
                  <form name="SaveGame" id="SaveGame" method="post" action="http://127.0.0.1/PHP/mine2.php" enctype="multipart/form-data">
                    <input type="submit" value="Save" id="save" onclick="save3()" class="button12" />
                    <input type="hidden" name="user_id" id="user_id">
                    <input type="hidden" name="book_id" id="book_id">
                    <input type="hidden" name="game_id" id="game_id">
                    <input type="hidden" name="site_id" id="site_id">
                  </form>
                  <script>
                    $("#SaveGame").submit(function(e) {
                      var form = $(this);
                      var url = form.attr('action');
                      $.ajax({
                        type: "POST",
                        url: url,
                        data: form.serialize(), // serializes the form's elements.
                        success: function(data) {
                          alert("The game has been saved!"); // show response from the php script.
                        }
                      });
                      e.preventDefault(); // avoid to execute the actual submit of the form.
                    });
                  </script>
</body>
</html>
mine2.php
    <?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
$link = mysqli_connect("127.0.0.1", "root", "", "mysql3");
// Check connection
if($link === false) {
    die("ERROR: Could not connect. " . mysqli_connect_error());
}
$user_id =$_POST['user_id'];
$book_id =$_POST['book_id'];
$game_id =$_POST['game_id'];
$site_id =$_POST['site_id'];
//if (mysql_query("INSERT INTO `components` (`user_id`, `book_id`, `game_id`, `site_id`) VALUES ('".$user_id."','".$book_id."','".$game_id."', '".$site_id."',)"));
mysqli_query($link ,""INSERT INTO components (user_id, book_id, game_id, site_id) VALUES ('".$user_id."','".$book_id."','".$game_id."', '".$site_id."')"") ; 
// Attempt insert query execution
//$sql = "INSERT INTO components (user_id, book_id, game_id, site_id) VALUES ('6', '6', '6', '6')";
//if(mysqli_query($link, $sql)){
//} else{
//}
// Close connection
mysqli_close($link);
?>
Guys, also I found this question: JS Prompt to PHP Variable Should I use something from there?
 
     
    