What should new URL("#") return?

[azu]

What should be the result of new URL("#")?
Browsers return different results.

In my understanding is that new URL("#") should throw a validation error.

1. scheme start state
   1. [skip] If c is an ASCII alpha, append c, lowercased, to buffer, and set state to scheme state.
   2. [match] Otherwise, if state override is not given, set state to no scheme state and decrease pointer by 1. → go to no schema state
2. no schema state
   1. [match] If base is null, or base’s cannot-be-a-base-URL flag is set and c is not U+0023 (#), validation error, return failure. → throw validation error

if ( base === null || (cannot-be-a-base-URL && c !== "#")){
  throw validation error
}

state value

• base is null (initial value)
• cannot-be-a-base-URL flag is not set
• c is #

---

Test results:

• Firefox 80.0 → throw TypeError: URL constructor: # is not a valid URL.
• Chrome 85 → return URL {href: "about:blank#", origin: "null", protocol: "about:", username: "", password: "", …}
• Safari 13.1.2 → return URL {href: "about:blank#", origin: "null", protocol: "about:", username: "", password: "", …}
• Node.js 14.5 → throw TypeError [ERR_INVALID_URL]: Invalid URL: #
• whatwg-url → throw Error

I can not found this test in wpt/url.

📝 Memo:
I've noticed this different result when comparing aTag.href with URL object.
Some <a> element starts with fragment like <a href="#fragment"> and new URL(a.href) got different results.
However, new URL(a.href, location.href) is not problem.

[annevk]

We should add a test for this. Chrome and Safari are wrong, but they might have matched an earlier version of the standard that mistakenly used about:blank as the default base URL: c2980ee. Although that would not explain new URL("?") throwing and new URL("about:blank?") not throwing, so they are probably just buggy.

[azu]

Thanks to confirm!

[annevk]

To close this issue two things will need to be done that are relatively straightforward:

1. New tests will need to be contributed to web-platform-tests (see README) for parsing # without base URL.
2. Bugs will need to be filed against Chrome and Safari (see https://github.com/whatwg/meta/blob/master/MAINTAINERS.md#handling-pull-requests for where exactly) for getting not throwing a TypeError as expected.

[achristensen07]

https://bugs.webkit.org/show_bug.cgi?id=216115

[domenic]

https://bugs.chromium.org/p/chromium/issues/detail?id=1227126