Re: [webcomponents] attachShadow must throw a TypeError when mode is omitted (#311)

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.

---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/311#issuecomment-137493824