Re: [heycam/webidl] Allow async iterators to specify return algorithms (#805)

Ms2ger approved this pull request.

Thanks and sorry for the delay.

> @@ -4307,6 +4307,21 @@ iteration, or resolves with a tuple containing two elements:
 1.  a value of the first type given in the declaration;
 1.  a value of the second type given in the declaration.
 
+The prose may also define an <dfn export>asynchronous iterator return</dfn> algorithm. This
+algorithm receives the instance of the [=interface=] that is being iterated, the async iterator
+itself, and a single argument value. This algorithm is invoked in the case of premature termination

And the single argument value is an {{any}} value?

> +        *   the platform object |object|,
+        *   the identifier "<code>return</code>", and
+        *   the type "<code>method</code>".
+
+        If this threw an exception |e|, then:
+        1.  Perform [=!=] [$Call$](|returnPromiseCapability|.\[[Reject]],
+            <emu-val>undefined</emu-val>, « |e| »).
+        1.  Return |returnPromiseCapability|.\[[Promise]].
+
+    1.  If |object| is not a [=default asynchronous iterator object=] for |interface|, then:
+        1.  Let |error| be a new {{ECMAScript/TypeError}}.
+        1.  Perform [=!=] [$Call$](|returnPromiseCapability|.\[[Reject]],
+            <emu-val>undefined</emu-val>, « |error| »).
+        1.  Return |returnPromiseCapability|.\[[Promise]].
+
+    1.  If |object|'s [=default asynchronous iterator object/ongoing promise=] is not undefined, then:

Check if this undefined needs an emu-val? I don't remember which way this one goes.

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