attachShadow must throw a TypeError when mode is omitted

[rniwa]

attachShadow must throw a TypeError when "mode" is omitted in ShadowRootInit as previously agreed in F2F.

[rniwa]

We should also throw when the value of mode doesn't match either "open" or "closed".

[domenic]

I think the correct way to do this is to make mode required in the definition of ShadowRootInit. Should be a one-line fix.

[domenic]

Actually the spec already takes care of this. When you convert a JS value to a ShadowRootMode, per IDL, first you do a ToString, and if it does not match "open" or "closed" (including if it is "undefined"), it will throw a TypeError.

[rniwa]

But it could still be omitted from the dictionary, right?

[domenic]

Yeah, I just re-read, and I was right the first time. Without required, if it is undefined (e.g. via omission from the JS object that gets converted into an IDL dictionary), the conversion to ShadowRootMode will not take place.

So yeah, just add required and it'll work as expected.

[hayatoito]

I thought it's required by default unless optional is specified. What's weird. :(
Where can I read the definition of required?
Is this the latest spec we should use? https://heycam.github.io/webidl/

[annevk]

No, dictionary members are always optional unless prefixed with required. And yes, that is the latest IDL.