Questions about jsfunfuzz grammar generation

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Hi! I'm trying to create a jsfunfuzz grammar. But there was no separate document, so I wrote here.
What I want is a mutated grammar js file, but when I run the command
(python3 -m funfuzz.js.loop --random-flags --compare-jit 20 mozilla-central ./js), only a js file close to a rapper is created. (jsfunfuzz.js)
I want to generate js file from the funfuzz and test it on another js engine.
Is there a way?