URL: Constructor should throw error if URL cannot be parsed

[aduth]

[type]: Bug report

What

The URL polyfill constructor should throw an error if passed an invalid URL.

new URL( 'invalid' );
// Expected: Uncaught TypeError: Failed to construct 'URL': Invalid URL
// Actual: (successfully returns new instance of URL)

For context, this affects us in that we use the throwing of an error as an indication of whether a given URL is a valid URL. Thus, without a thrown error, invalid URLs would be incorrectly reported as being valid when the polyfill is used.

https://github.com/WordPress/gutenberg/blob/59d7463/packages/url/src/is-url.js

(Related originating conversation: WordPress/gutenberg#20172 (comment))

Details

References:

If the given base URL or the resulting URL are not valid URLs, the JavaScript TypeError exception is thrown.

https://developer.mozilla.org/en-US/docs/Web/API/URL/URL

If parsedURL is failure, then throw a TypeError.

https://url.spec.whatwg.org/#dom-url-url

Other Implementations:

• https://github.com/jsdom/whatwg-url/blob/d97c651/lib/URL-impl.js#L19-L22
• https://github.com/zloirock/core-js/blob/4546ffe/packages/core-js/modules/web.url.js#L749-L750

Relevant Code:

https://github.com/Financial-Times/polyfill-library/blob/5360b0dd924cc08ca1a815e003033c7e489c7ab0/polyfills/URL/polyfill.js#L284-L452

[JakeChampion]

PR for this work --> #627