Gmail currently restricts certain file attachments (e.g. .exe, .msc, and .bat) for security reasons, and starting on February 13, 2017, we will not allow .js file attachments as well. Similar to other restricted file attachments, you will not be able to attach a .js file and an in-product warning will appear, explaining the reason why.
Launching to Rapid release on February 13, 2017, with Scheduled release coming 2 weeks afterward
Available to all G Suite editions
Full rollout (1-3 days for feature visibility)
Reference by Google.com