It is inevitable that you will have to use a “plugin” to your definition, but…
Here’s the good news:
There’s a really good, easy to use, simple to code jQuery-File-Upload by blueimp that you can Download Here.
You wanted it simple:
Since you are looking for it to be a simple, basic jQuery… You can Look Here for a basic tutorial on what you’re looking for.
Side note:
It isn’t so much a site plug-in as a javascript library to do what you want to for a “Basic File jQuery uploader.
Other option:
Your only other option without uploading javascript libraries would be to use an iFrame that you post the uploaded iFrame to, which can simulate jQuery, in the way that you don’t have to reload the page for it to upload the file.
solved jquery ajax fileupload [closed]