A while back, Gmail began blocking .js file attachments, but I didn't realize until today that this means my old JavaScript file attachments would be retroactively blocked. I tracked down an email from two years ago with a JavaScript file attached that I needed, but I couldn't download it!
I was eventually able to get it by doing "Show Original" in Gmail and copy/pasting the base64-encoded attachment data and decoding it. But it made me nervous about using Gmail as a way to hang on to files, since things I attach now might not be available later.
I had this same issue. Google also blocked .jar and .zip if I remember. I had lost some old school projects that I tried to recover, which we're turned in via email. I couldn't download the attachments for this, despite the fact I sent them in the first place! Much less, why couldn't I allow someone to send me a .js file I wanted it? It's a weird restriction to not even be given a choice.
I was eventually able to get it by doing "Show Original" in Gmail and copy/pasting the base64-encoded attachment data and decoding it. But it made me nervous about using Gmail as a way to hang on to files, since things I attach now might not be available later.