I fixed the slightly different interface. Here I adopt a 3rd-party library which also does not consider protocol-relative urls (//123.example.com) as valid so we have to patch it (and test) similarly to #123. What do you think?

First and foremost, I'm deeply appreciative of the enthusiasm and effort you're putting into my little lib here. I want you to know that I'm sincere.

Unfortunately I'm pretty adamant that I don't want to adopt any new code that can come from an existing package instead. I would be shocked if there wasn't one that could validate urls properly by now. I'm happy to help search for a suitable replacement when I do have time this week, and would be happy to commit to your fork so you get the credit for the work.

I tried the following:

• "everything-validator": "^1.0.2"
• "is-http-url": "^2.0.0"
• "is-relative-uri": "^1.0.16"
• "is-valid-http-url": "^1.0.3"
• "valid-url": "^1.0.9"
• "url-regexp": "^1.0.2"
• "url-validate": "^1.0.1"
• "url-validation": "^2.1.0"
• "url-validator": "^2.0.3"
• "url_validator": "^1.0.4",
• "urlint": "^1.9.17",
• "valid-url": "^1.0.9"
• "valid-url-utf8": "^1.0.7"
• "validate-utility": "0.0.2"

From these only url-validator, an "opinionated URL validator", accepts protocol-relative URLs as valid. Its last release is from 6 years ago and its Github repo and organization were deleted so personally I'd drop support as well (in #123). Please let me know if you change your mind, or if you find a more active project for replacement.