Integrate box into a website to select file from user's account

I have a website that uses box currently that does a popup on the page and the user selects files they wish to upload (to our site) from their account.  We created this code 4 years ago and it's still working, but I cannot seem to find the documentation for it.  Meaning its either deprecated or there is a better way.

It uses the select.js found here https://app.box.com/js/static/select.js

Can someone point me in the current option to download a file from a users box account (after they login) or to the documentation on the javascript found above?

Thanks!