TechSpot means tech analysis and advice you can trust. Read our ethics statement.
Similar to how it handles other restricted attachments, if you try to attach a .js file to an email on or after the 13th, you'll get a notification that says it's blocked "because its content presents a potential security issue." The service will detect .js files even if they're sent in compressed form as a .zip, for example.
If you still need to send .js files for legitimate reasons, Google suggests you use Google Drive, Google Cloud Storage, or other storage solutions to share or send your files
It's unclear Google will also show a warning when users receive emails with JS files attached.