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

domenic commented on this pull request.



> +
+<h4 id="es-observable-array-deleteProperty"><code>deleteProperty</code></h4>
+
+<div algorithm="observable array exotic object deleteProperty trap">
+    The steps for the <code>deleteProperty</code> proxy trap for
+    [=observable array exotic objects=], given |O| and |P|, are as follows:
+
+    1.  Let |handler| be the <emu-val>this</emu-val> value.
+    1.  If |P| is "length", then return <emu-val>false</emu-val>.
+    1.  If |P| [=is an array index=], then:
+        1.  Let |oldLen| be |handler|.\[[BackingList]]'s [=list/size=].
+        1.  Let |index| be [=!=] [$ToUint32$](|P|).
+        1.  If |index| ≠ |oldLen| &minus; 1, then return
+            <emu-val>false</emu-val>.
+        1.  Perform the algorithm steps given by |handler|.\[[DeleteAlgorithm]], given
+            |handler|.\[[BackingList]][|index|] and |index|.

We've defined the [[DeleteAlgorithm]] as a web spec "algorithm", not as an ES-spec abstract operation, so it isn't generally callable with function-call notation.

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