Validate with function, allow duplicattes

[baranovxyz]

This is the best I can do. I don't get why some code does not reformat to your initial code.

I think using prettier can give more stable results. I can add it to work with eslint, if you want.

It must be I used prettier to get this result, but then I removed it from dependencies, but now eslint can't reformat it back.

This is instead of #70

[baranovxyz]

This result (code) i get by running npm run lint:fix

[matiastucci]

Thanks :)