in ajax you may not have the opportunity to upload a file. but With javascript you can this is how you can do:
<form name=fileuploader id=fileuploader method=post action='upload_handle.ext' enctype="multipart/form-data" target='UploadedFrame'>
<input type='file' name='csv' id='csv' onchange='document.getElementById("fileuploader").submit()' Title='Select File Name'>
</form>
<iframe id='UploadedFrame' name='UploadedFrame' style='display:none'></iframe>
with HTML5 you can also work with size and other issues