[URL] URL polyfill isn't compatible with the spec: doesn't throw on partial URLs

[sgomes]

Description

The URL polyfill does not throw an exception on new URL( string ) where string is not an absolute URL and no base URL is provided.

Live Demo

https://jsbin.com/dahuqeqoyu/edit?html,console,output

Steps to Reproduce

1. Ensure that the URL polyfill is active by e.g. specifying window.forceJURL = true before loading it
2. Attempt to create a URL object from a partial URL and no base, e.g. new URL('/path')
3. Observe whether an exception is thrown or not

Expected Results

It's expected that an exception is thrown if a URL string without a scheme is provided and no base is provided, as per https://url.spec.whatwg.org/#no-scheme-state (emphasis mine):

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.

Modern browsers that implement the spec behave as expected.

Actual Results

An error is not thrown, and instead a URL object is created with most of its properties set to empty strings, and the protocol property set to ":".

Browsers Affected

Any browser in which the polyfill is applied, whether it's because there's no native support for URL (e.g. IE11), or because the polyfill is forced (window.forceJURL = true).

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[sgomes]

Adding a note that the polyfill is very much still being used, so it may still be worth it to fix this issue.

[sgomes]

Adding a note that this bug is still present in the latest version, @webcomponents/[email protected].

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[xiaoxiangmoe]

@bicknellr Can I create a PR to fix this bug?

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.