[question] How to get FILE* stdout / stderr from JavaScript?

I mapped `_fopen` , but it returns NULL:
```
> fopen('/dev/stderr', 'w')
0
> fopen('/dev/stdout', 'w')
0
```

Also, mapping `_fputc` produces `Uncaught RuntimeError: function signature mismatch`

Does anybody have an example of writing a `\n` to `stderr` from JavaScript?