Expose the error from ReadableStream for Response methods via `err.cause`

[saschanaz]

new Response(new ReadableStream({
  pull(c) {
    c.error("oh");
  }
})).text()

Different browsers do different things:

• Firefox logs a console message (invisible to JS)
• Safari passes it to the message of DOMException (and thus objects may become [object Object] by stringification)
• Chrome does not expose it in any way.

Should the spec define a way to do this? Maybe use the new error.cause?

[domenic]

I like using error.cause. The main issue here though is cross-realm serialization. I guess that mostly works for errors these days, although I wish someone (not me) had the time to make it work with the new error types and capabilities. I tried in whatwg/html#5749 but got stalled. (I guess Firefox implemented something without a spec.)

[annevk]

Seems reasonable, might require some Web IDL changes to be able to set this property?

[saschanaz]

Alright, in that case this depends on whatwg/webidl#1179.