Re: [heycam/webidl] Introduce the observable array type (proxy-based) (#840)

bzbarsky commented on this pull request.



> @@ -13629,6 +13803,250 @@ internal method as follows.
     1.  Return <a abstract-op>OrdinaryGetOwnProperty</a>(|O|, |P|).
 </div>
 
+<h3 id="es-observable-arrays">Observable array exotic objects</h3>
+
+An <dfn>observable array exotic object</dfn> is a specific type of ECMAScript
+[=Proxy exotic object=] which is created using the proxy traps defined in this section. They are
+defined in this manner because the ECMAScript specification includes special treatment for
+[=Proxy exotic objects=] that have <code>Array</code> instances as their proxy target, and we want
+to ensure that [=observable array types=] are exposed to ECMAScript code with this special treatment
+intact.

> "black-box-identical" to having "an IDL object with an indexed getter and indexed setter, but returning true from IsArray and with Array.prototype on the proto chain"

Now that I have read the details, that's not quite the case. The behavior of `defineProperty` with various interesting attributes set in the descriptor is different, `length` is an own property instead of a prototype one, etc.  The two things are similar, and can share a lot of implementation, I suspect, but are not quite identical.

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