api.URL.pathname - Two rounds of modifications to opaque path trailing space

[Josh-Cena]

What type of issue is this?

Missing compatibility data

What information was incorrect, unhelpful, or incomplete?

See mdn/content#23320. The URL spec went through two rounds of modifications related to trailing spaces in opaque paths that both ended up being implemented, and this should be documented because currently browsers are disagreeing.

What browsers does this problem apply to, if applicable?

No response

What did you expect to see?

Data for whatwg/url#728 and whatwg/url#844

Did you test this? If so, how?

Try the following code:

const url = new URL("data:text/plain,Hello #frag");
console.log(JSON.stringify(url.pathname));
url.hash = "";
console.log(JSON.stringify(url.pathname));

Several years ago, the result was

"text/plain,Hello "
"text/plain,Hello "

About 2 years ago, and Chrome and Firefox as of now, the result is

"text/plain,Hello "
"text/plain,Hello"

But, in Safari TP, the result has been changed to

"text/plain,Hello%20"
"text/plain,Hello%20"

Can you link to any release notes, bugs, pull requests, or MDN pages related to this?

No response

Do you have anything more you want to share?

No response

MDN URL

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

MDN metadata

MDN page report details

• Query: api.URL.pathname
• Report started: 2025-09-15T03:48:43.593Z