Function addQueryArgs adds query args in the incorrect place when the URL contains a URL fragment. According to RFC 3986, query args come before the URL fragment:

relative-ref = relative-part [ "?" query ] [ "#" fragment ]

Therefore, when invoking addQueryArgs as follows:

wp.url.addQueryArgs( 'https://example.com/page/#fragment', { param: 'value' } )

the expected result is:

https://example.com/page/?param=value#fragment

but the invalid result we get is:

https://example.com/page/#fragment?param=value

Additional context

• Tested with Gutenberg 6.1.1.