In the Mac client under raw data format options there is a Javascript option. I’ve tried all sorts of things to make that work and can’t. Documentation doesn’t even mention it.
All my searches come up with things relating to testing or using the JSON format.
And, as @arlem mentioned, it helps you with the syntax highlighting in the raw area and also as soon as you select that option, it sets the Content-Type header as application/javascript (you can see the Header tab and you’ll find that header)