Hide submit button until a file has been chosen thorugh pure javascript

I want to show submit button only after a file is selected. I can do this with jquery but i have not used jquery in any part of page so to avoid some spaces i need this to be done through pure Javascript.

<form action="" method="POST" enctype="multipart/form-data">
<input type="file" name="uploadfile" id="pimage"/> 
<input type="submit" name="submit" value="Confirm">
</form>