How does access to .cssRules behave before the sheet is "done loading"

[bzbarsky]

E.g. before all the @imports have finished. Does it throw? Does it allow mutation of the rule list while loads are still in progress? Something else?

[calebdwilliams]

In the web components issue 468, @rniwa proposed disallowing @import in the constructible stylesheet spec. Not sure what the pros and cons are of that, but just trying to connect some dots.

[bzbarsky]

Disallow in what sense? Not parsed (i.e. dropped from the rule list)? Throws? Not loaded? Something else?

[calebdwilliams]

Not sure, like I said, just trying to connect some dots. For that particular issue, was hoping we would be able to fetch an external resource for customElements styles, but looks like @annevk agreed. Maybe someone should add this as a separate issue for discussion? I'm not sure I'm qualified to have any real opinions here, just wanting to see the thing move froward.

[annevk]

FWIW, I think this should work the same way as <link rel=stylesheet> or <style> deal with it, though as I noted in #21 we should maybe define those properly first.

[TakayoshiKochi]

Let me close this as #25 concludes we disallow @imports.

[TakayoshiKochi]

From the discussion at whatwg/html#2997 (especially from Tab's whatwg/html#2997 (comment)), conceptually the sheet is parsed atomically, and therefore when <link rel=stylesheet> or <style>'s .sheet is available, its .cssRules is also available.

For this spec, the constuctor will produce a CSSStyleSheet with empty rules, and for the factory method, it returns a promise and once it resolves, its return value (a new CSSStyleSheet object) should have .cssRules ready.

So let's not make a CSSStyleSheet object visible until its all dependent loading/parsing is done.

(basically this adds nothing to what @annevk already said above)

[rakina]

Closed with #33 (like the above comment says, we aren't resolving Promise until it's done loading)