Use prototype-less return object (#1)

Author: jridgewell

index.html

@@ -2261,9 +2261,10 @@ <h1><span class="secnum">2.1</span> Array.prototype.groupBy ( <var>callbackfn</v
       <p><var>callbackfn</var> is called with three arguments: the value of the element, the index of the element, and the object being traversed.</p>
       <p><code>groupBy</code> does not directly mutate the object on which it is called but the object may be mutated by the calls to <var>callbackfn</var>.</p>
       <p>The range of elements processed by <code>groupBy</code> is set before the first call to <var>callbackfn</var>. Elements which are appended to the array after the call to <code>groupBy</code> begins will not be visited by <var>callbackfn</var>. If existing elements of the array are changed their value as passed to <var>callbackfn</var> will be the value at the time <code>groupBy</code> visits them; elements that are deleted after the call to <code>groupBy</code> begins and before being visited are not visited.</p>
+      <p>The return value of <code>groupBy</code> is an object that does not inherit from <var>Object.prototype</var>.</p>
     </div></emu-note>
     <p>When the <code>groupBy</code> method is called with one or two arguments, the following steps are taken:</p>
-    <emu-alg><ol><li>Let <var>O</var> be ?&nbsp;<emu-xref aoid="ToObject" id="_ref_0"><a href="https://tc39.es/ecma262/#sec-toobject">ToObject</a></emu-xref>(<emu-val>this</emu-val> value).</li><li>Let <var>len</var> be ?&nbsp;<emu-xref aoid="LengthOfArrayLike" id="_ref_1"><a href="https://tc39.es/ecma262/#sec-lengthofarraylike">LengthOfArrayLike</a></emu-xref>(<var>O</var>).</li><li>If <emu-xref aoid="IsCallable" id="_ref_2"><a href="https://tc39.es/ecma262/#sec-iscallable">IsCallable</a></emu-xref>(<var>callbackfn</var>) is <emu-val>false</emu-val>, throw a <emu-val>TypeError</emu-val> exception.</li><li>Let <var>k</var> be 0.</li><li>Let <var>obj</var> be !&nbsp;OrdinaryObjectCreate(%Object.prototype%).</li><li><emu-xref href="#assert"><a href="https://tc39.es/ecma262/#assert">Assert</a></emu-xref>: <var>obj</var> is an extensible ordinary object with no own properties.</li><li>Repeat, while <var>k</var> &lt; <var>len</var><ol><li>Let <var>Pk</var> be !&nbsp;<emu-xref aoid="ToString" id="_ref_3"><a href="https://tc39.es/ecma262/#sec-tostring">ToString</a></emu-xref>(<var>k</var>).</li><li>Let <var>kValue</var> be ?&nbsp;<emu-xref aoid="Get" id="_ref_4"><a href="https://tc39.es/ecma262/#sec-get-o-p">Get</a></emu-xref>(<var>O</var>, <var>Pk</var>).</li><li>Let <var>propertyKey</var> be ?&nbsp;<emu-xref aoid="ToPropertyKey" id="_ref_5"><a href="https://tc39.es/ecma262/#sec-topropertykey">ToPropertyKey</a></emu-xref>(? <emu-xref aoid="Call" id="_ref_6"><a href="https://tc39.es/ecma262/#sec-call">Call</a></emu-xref>(<var>callbackfn</var>, <var>thisArg</var>, « <var>kValue</var>, <var>k</var>, <var>O</var> »)).</li><li>Let <var>seen</var> be ?&nbsp;<emu-xref aoid="HasOwnProperty" id="_ref_7"><a href="https://tc39.es/ecma262/#sec-hasownproperty">HasOwnProperty</a></emu-xref>(<var>obj</var>, <var>propertyKey</var>).</li><li>If <var>seen</var> is <emu-val>true</emu-val>, then<ol><li>Let <var>arr</var> be !&nbsp;<emu-xref aoid="Get" id="_ref_8"><a href="https://tc39.es/ecma262/#sec-get-o-p">Get</a></emu-xref>(<var>obj</var>, <var>propertyKey</var>).</li></ol></li><li>Else<ol><li>Let <var>arr</var> be ?&nbsp;<emu-xref aoid="ArraySpeciesCreate" id="_ref_9"><a href="https://tc39.es/ecma262/#sec-arrayspeciescreate">ArraySpeciesCreate</a></emu-xref>(O, 0).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_10"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>obj</var>, <var>propertyKey</var>, <var>arr</var>).</li></ol></li><li>Perform ?&nbsp;<emu-xref aoid="Call" id="_ref_11"><a href="https://tc39.es/ecma262/#sec-call">Call</a></emu-xref>(%Array.prototype.push%, <var>arr</var>, <var>kValue</var>).</li><li>Set <var>k</var> to <var>k</var> + 1.</li></ol></li><li>Return <var>obj</var>.</li></ol></emu-alg>
+    <emu-alg><ol><li>Let <var>O</var> be ?&nbsp;<emu-xref aoid="ToObject" id="_ref_0"><a href="https://tc39.es/ecma262/#sec-toobject">ToObject</a></emu-xref>(<emu-val>this</emu-val> value).</li><li>Let <var>len</var> be ?&nbsp;<emu-xref aoid="LengthOfArrayLike" id="_ref_1"><a href="https://tc39.es/ecma262/#sec-lengthofarraylike">LengthOfArrayLike</a></emu-xref>(<var>O</var>).</li><li>If <emu-xref aoid="IsCallable" id="_ref_2"><a href="https://tc39.es/ecma262/#sec-iscallable">IsCallable</a></emu-xref>(<var>callbackfn</var>) is <emu-val>false</emu-val>, throw a <emu-val>TypeError</emu-val> exception.</li><li>Let <var>k</var> be 0.</li><li>Let <var>obj</var> be !&nbsp;OrdinaryObjectCreate(null).</li><li><emu-xref href="#assert"><a href="https://tc39.es/ecma262/#assert">Assert</a></emu-xref>: <var>obj</var> is an extensible ordinary object with no own properties.</li><li>Repeat, while <var>k</var> &lt; <var>len</var><ol><li>Let <var>Pk</var> be !&nbsp;<emu-xref aoid="ToString" id="_ref_3"><a href="https://tc39.es/ecma262/#sec-tostring">ToString</a></emu-xref>(<var>k</var>).</li><li>Let <var>kValue</var> be ?&nbsp;<emu-xref aoid="Get" id="_ref_4"><a href="https://tc39.es/ecma262/#sec-get-o-p">Get</a></emu-xref>(<var>O</var>, <var>Pk</var>).</li><li>Let <var>propertyKey</var> be ?&nbsp;<emu-xref aoid="ToPropertyKey" id="_ref_5"><a href="https://tc39.es/ecma262/#sec-topropertykey">ToPropertyKey</a></emu-xref>(? <emu-xref aoid="Call" id="_ref_6"><a href="https://tc39.es/ecma262/#sec-call">Call</a></emu-xref>(<var>callbackfn</var>, <var>thisArg</var>, « <var>kValue</var>, <var>k</var>, <var>O</var> »)).</li><li>Let <var>seen</var> be ?&nbsp;<emu-xref aoid="HasOwnProperty" id="_ref_7"><a href="https://tc39.es/ecma262/#sec-hasownproperty">HasOwnProperty</a></emu-xref>(<var>obj</var>, <var>propertyKey</var>).</li><li>If <var>seen</var> is <emu-val>true</emu-val>, then<ol><li>Let <var>arr</var> be !&nbsp;<emu-xref aoid="Get" id="_ref_8"><a href="https://tc39.es/ecma262/#sec-get-o-p">Get</a></emu-xref>(<var>obj</var>, <var>propertyKey</var>).</li></ol></li><li>Else<ol><li>Let <var>arr</var> be ?&nbsp;<emu-xref aoid="ArraySpeciesCreate" id="_ref_9"><a href="https://tc39.es/ecma262/#sec-arrayspeciescreate">ArraySpeciesCreate</a></emu-xref>(O, 0).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_10"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>obj</var>, <var>propertyKey</var>, <var>arr</var>).</li></ol></li><li>Perform ?&nbsp;<emu-xref aoid="Call" id="_ref_11"><a href="https://tc39.es/ecma262/#sec-call">Call</a></emu-xref>(%Array.prototype.push%, <var>arr</var>, <var>kValue</var>).</li><li>Set <var>k</var> to <var>k</var> + 1.</li></ol></li><li>Return <var>obj</var>.</li></ol></emu-alg>
     <emu-note><span class="note">Note 2</span><div class="note-contents">
       <p>The <code>groupBy</code> function is intentionally generic; it does not require that its <emu-val>this</emu-val> value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.</p>
     </div></emu-note>

spec.emu

@@ -30,14 +30,15 @@ location: https://tc39.es/proposal-array-grouping/
       <p>_callbackfn_ is called with three arguments: the value of the element, the index of the element, and the object being traversed.</p>
       <p>`groupBy` does not directly mutate the object on which it is called but the object may be mutated by the calls to _callbackfn_.</p>
       <p>The range of elements processed by `groupBy` is set before the first call to _callbackfn_. Elements which are appended to the array after the call to `groupBy` begins will not be visited by _callbackfn_. If existing elements of the array are changed their value as passed to _callbackfn_ will be the value at the time `groupBy` visits them; elements that are deleted after the call to `groupBy` begins and before being visited are not visited.</p>
+      <p>The return value of `groupBy` is an object that does not inherit from _Object.prototype_.</p>
     </emu-note>
     <p>When the `groupBy` method is called with one or two arguments, the following steps are taken:</p>
     <emu-alg>
       1. Let _O_ be ? ToObject(*this* value).
       1. Let _len_ be ? LengthOfArrayLike(_O_).
       1. If IsCallable(_callbackfn_) is *false*, throw a *TypeError* exception.
       1. Let _k_ be 0.
-      1. Let _obj_ be ! OrdinaryObjectCreate(%Object.prototype%).
+      1. Let _obj_ be ! OrdinaryObjectCreate(null).
       1. Assert: _obj_ is an extensible ordinary object with no own properties.
       1. Repeat, while _k_ &lt; _len_
         1. Let _Pk_ be ! ToString(_k_).