The Perl package is GPL. He took definitions from it, ported them to JS, and licensed them as MIT. "Is license violation theft?" is one of those questions like "Is piracy theft?", but it does undermine his insistence that he should be allowed commercialise the result.

It depends on whether you think copying a list of constants from what is essentially an “API” is copyright infringement.

It’s a contentious topic, but last I heard people here tend to believe it isn’t (as long as it’s Google copying Oracle’s stuff)

Those sound like two distinct things to me:

- Copying an interface for the purpose of providing a compatible implementation (what Google allegedly did - although of course part of the debate is whether they also copied any of the implementation)

- Copying parts of the implementation, not for the purpose of compatibility (what faker.js did - in this case, copying constants)

IIRC US copyright law gives very little protection to compilation of non-copyrightable data (look up copyright status of telephone directories). The argument is that it's just public domain factual information bundled together.

The faker libraries are all that -- compilations of mostly non-copyrightable facts.

I'm not saying faker.js did no wrong, just saying if hypothetically a purported copyright owner sued him, they would have a really hard time proving substantial infringement happened given the available precedents.