Google is set to stop JS files to be sent as an attachment, JS files within archieves are not left out. This action is set to prevent its users from malicious mails which most times attach different forms of executable programs. These consists of batch files (.bat), standard window executables (.exe) and Javascript files (.JS).
During web application development, JS files are most times loaded as an integral part of the web pages. Therefore, an opening of an unknown JS file on windows can be fatal. Since by default, it runs inside windows script host thereby leading to the window executable program to be run by these scripts.
It has not been said if an alert of any sort will be given when emails with JS file attachment is been received.