URL serialization

URL serialization produces the textual spelling of a structured URL record. It is the output side of processing that begins with a URL parser. The WHATWG serializer returns an ASCII string and can optionally omit the fragment identifier.^[ref]

A worked example separates the stages. Constructing new URL('https://EXAMPLE.org:443/a/../b?q=hello%20world~#top') gives href equal to https://example.org/b?q=hello%20world~#top. Lowercasing the host, removing the default port and resolving the parent-directory segment happen during parsing; the serializer exposes the resulting record.

Now call u.searchParams.sort() on that object. Even though there is only one query pair to sort, href becomes https://example.org/b?q=hello+world%7E#top. The decoded query value is unchanged, but URLSearchParams has rewritten its spelling using form URL encoding. Thus changing the query through an API can alter its percent-encoding without changing the value returned by that API.^[ref]

A serialized address is also different from a browser's chosen display text or a server's returned content. Comparing those different outputs answers different questions.