It would be a fun test to run. But I'm not encouraged by the fact that the existing brotli dictionary already contains a bunch of javascript specific stuff:

https://gist.github.com/klauspost/2900d5ba6f9b65d69c8e

brotli literally already has a tokens for function/return/throw/indexOf(/.match/.length/etc.

Also verify after decompress is not without tradeoffs. On one hand we have folks like github who can't change the version of zlib because people rely on identical .tar.gz. https://news.ycombinator.com/item?id=34586917

On the other hand we have a whole lot of iffy stuff you can do to make programs decompressing content use large amounts of resources https://en.wikipedia.org/wiki/Zip_bomb which makes "decompress this potentially untrusted file so that I can validate it's safe to use" hard.