非同期複数ファイルのアップロードに jQuery の `.submit()` と `.ajax()` を使用する方法

<form enctype="multipart/form-data" action="upload.php" method="post">
    <input name="file[]" type="file">
    <button class="add_more">Add More Files</button>
    <input type="button">

$(document).ready(function(){
    $('.add_more').click(function(e){
        e.preventDefault();
        $(this).before("<input name='file[]' type='file'>");
    });
});

for($i=0; $i<count($_FILES['file']['name']); $i++){
    $target_path = "uploads/";
    $ext = explode('.', basename( $_FILES['file']['name'][$i]));
    $target_path = $target_path . md5(uniqid()) . "." . $ext[count($ext)-1]; 

    if(move_uploaded_file($_FILES['file']['tmp_name'][$i], $target_path)) {
        echo "The file has been uploaded successfully <br />";
    } else{
        echo "There was an error uploading the file, please try again! <br />";
    }
}

$('body').on('click', '#upload', function(e){
    e.preventDefault();
    var formData = new FormData($(this).parents('form')[0]);

    $.ajax({
        url: 'upload.php',
        type: 'POST',
        xhr: function() {
            var myXhr = $.ajaxSettings.xhr();
            return myXhr;
        },
        success: function (data) {
            alert("Data Uploaded: "+data);
        },
        data: formData,
        cache: false,
        contentType: false,
        processData: false
    });
    return false;
});