check-usernames.php

<?php
    // filename: check-usernames.php

    // mendeteksi pengiriman form ke halaman ini
    if (isset($_POST["q"])) {
        echo "Anda memilih username <strong>". $_POST["q"] ."</strong>";
    }
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.2.3/dist/css/bootstrap.min.css" integrity="sha384-rbsA2VBKQhggwzxH7pPCaAqO46MgnOM80zW1RWuH61DGLwZJEdK2Kadq2F9CUG65" crossorigin="anonymous">
    <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.2.3/dist/js/bootstrap.min.js" integrity="sha384-cuYeSxntonz0PPNlHhBs68uyIAVpIIOZZ5JqeqvYYIcEL727kskC66kF92t6Xl2V" crossorigin="anonymous"></script>
    <script src="https://code.jquery.com/jquery-3.7.1.min.js" integrity="sha256-/JqT3SQfawRcv/BIHPThkBvs0OEvtFFmqPF/lYI/Cxo=" crossorigin="anonymous"></script>
</head>
<body>
<form action="<?= $_SERVER["PHP_SELF"]; ?>" id="searchForm" method="post">
  <label for="q">Username:</label>
  <input type="text" name="q" id="q" placeholder="Pilih username...">
  <span id="result" role="alert"></span><br>
  <input type="submit" id="submit" class="btn btn-primary" value="Daftar">
</form>

<script>
    $(function(){
        // event blur (kehilangan fokus) pada text input, dari penekanan tab atau klik di luar input
        $("#q").blur(function() {
            $("#result").hide();
            let uname = $(this).val(); // mengambil teks dari input
            let url = "ajax-check-usernames.php";
            // mengirim data menggunakan POST, via jQuery
            var posting = $.post( url, { q: uname } );
            // aksi yang dilakukan setelah posting selesai
            posting.done(function(data) {
                if (data.indexOf("tersedia") != -1) {
                    $("#result").removeClass().addClass("alert alert-success fade show");
                    $("#submit").prop("disabled",false);
                } else {
                    $("#result").removeClass().addClass("alert alert-warning fade show");
                    $("#submit").prop("disabled",true);
                }
                $("#result").show();
                $("#result").empty().append(data).fadeOut(4000);
            });
        });
    });
</script>
</body>
</html>