.js is a Javascript file.
I would definitely not open any files from a dropbox unless you know the owner and know the files in it are okay.
The note that came with the notification said "Send 1 btc to Alan. Leave 2.7 btc in main wallet".
To be honest this is some good hacking technique, I was so tempted to open it to see if any bitcoins would fall out, lucky I posted here then scanned it!