Pakai parameter pada javascript

gimana sih cara pake parameter pada javascript ? ini kode saya.. tapi ada error di baris 26 yang katanya Undefined variable : data tapi kodenya tetep jalan, hanya saja ada peringatan error

<?php
session_start();
require 'koneksi.php';

if(!isset($_SESSION['login'])){
	header("Location: ../login.php");
	exit;
}

function hapusPertanyaan($data){
	global $conn;

	$id = $_GET['id'];

	mysqli_query($conn, "DELETE FROM pertanyaan WHERE id = '$id'");

	return mysqli_affected_rows($conn);
}

 ?>

 <script src="https://unpkg.com/sweetalert/dist/sweetalert.min.js"></script>

 <?php
$url = $_SERVER['HTTP_REFERER'];
if(hapusPertanyaan($data) > 0){
	echo "<script>
			swal({
				text: 'Pertanyaanmu berhasil dihapus!',
				icon: 'success'
				}).then(function(){
				setTimeout(document.location.href = '$url', 100);
				})
		</script>";
}else{
	echo "<script>
			swal({
				text: 'Pertanyaanmu gagal dihapus!',
				icon: 'error'
				}).then(function(){
				setTimeout(document.location.href = '$url', 100);
				})
		</script>";
}

  ?>