如何使用 PHP 實作 jQuery AJAX 檔案上傳？

$('#upload').on('click', function() {
    var file_data = $('#sortpicture').prop('files')[0];
    var form_data = new FormData();
    form_data.append('file', file_data);
    $.ajax({
        url: 'upload.php', // Point to the server-side PHP script
        dataType: 'text', // Expect text back from the PHP script
        cache: false,
        contentType: false,
        processData: false,
        data: form_data,
        type: 'post',
        success: function(php_script_response) {
            alert(php_script_response); // Display any response from the PHP script
        }
    });
});

<?php

if (0 < $_FILES['file']['error']) {
    echo 'Error: ' . $_FILES['file']['error'] . '<br>';
} else {
    move_uploaded_file($_FILES['file']['tmp_name'], 'uploads/' . $_FILES['file']['name']);
}

?>