您好。向此表单添加进度条的最佳方法是什么?
<form action="upload.php" method="post" enctype="multipart/form-data">
<center><p> <input type='file' size='58' style='height: 30px; font-size: 18px' name='filename'></p>
<input type='image' src='<?php echo $menu_upload_button; ?>'>
</form>
谢谢。