From 951513d3f1107b8cf77ef5756883d406120c365a Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <justin@ridgewell.name>
Date: Tue, 29 Nov 2022 10:41:43 -0500
Subject: [PATCH] [spec] Convert to static factory methods

Co-authored-by: Justin Ridgewell <justin@ridgewell.name>
Co-authored-by: Jordan Harband <ljharb@gmail.com>
---
 index.html |  82 +++++++++++++---------------
 spec.emu   | 157 +++++++++++++++++++++++++----------------------------
 2 files changed, 113 insertions(+), 126 deletions(-)

diff --git a/index.html b/index.html
index d988f5c..f17332e 100644
--- a/index.html
+++ b/index.html
@@ -1149,7 +1149,7 @@
 });
 
 let sdoMap = JSON.parse(`{}`);
-let biblio = JSON.parse(`{"refsByClause":{"sec-array.prototype.group":["_ref_0","_ref_1","_ref_2","_ref_3","_ref_4","_ref_5","_ref_6","_ref_7","_ref_8","_ref_9"],"sec-array.prototype.grouptomap":["_ref_10","_ref_11","_ref_12","_ref_13","_ref_14","_ref_15","_ref_16","_ref_17","_ref_18"],"sec-add-value-to-keyed-group":["_ref_19"],"sec-array.prototype-@@unscopables":["_ref_20","_ref_21","_ref_22","_ref_23","_ref_24","_ref_25","_ref_26","_ref_27","_ref_28","_ref_29","_ref_30","_ref_31","_ref_32"]},"entries":[{"type":"clause","id":"sec-scope","titleHTML":"Scope","number":"1"},{"type":"clause","id":"sec-array.prototype.group","title":"Array.prototype.group ( callbackfn [ , thisArg ] )","titleHTML":"Array.prototype.group ( <var>callbackfn</var> [ , <var>thisArg</var> ] )","number":"2.1"},{"type":"clause","id":"sec-array.prototype.grouptomap","title":"Array.prototype.groupToMap ( callbackfn [ , thisArg ] )","titleHTML":"Array.prototype.groupToMap ( <var>callbackfn</var> [ , <var>thisArg</var> ] )","number":"2.2"},{"type":"op","aoid":"AddValueToKeyedGroup","refId":"sec-add-value-to-keyed-group"},{"type":"clause","id":"sec-add-value-to-keyed-group","title":"AddValueToKeyedGroup ( groups, key, value )","titleHTML":"AddValueToKeyedGroup ( <var>groups</var>, <var>key</var>, <var>value</var> )","number":"2.3","referencingIds":["_ref_7","_ref_16"]},{"type":"clause","id":"sec-array.prototype-@@unscopables","titleHTML":"Array.prototype [ @@unscopables ]","number":"2.4"},{"type":"clause","id":"sec-properties-of-the-array-prototype-object","titleHTML":"Properties of the Array Prototype Object (22.1.3)","number":"2"},{"type":"clause","id":"sec-copyright-and-software-license","title":"Copyright & Software License","titleHTML":"Copyright &amp; Software License","number":"A"}]}`);
+let biblio = JSON.parse(`{"refsByClause":{"sec-object.groupby":["_ref_0","_ref_1","_ref_2"],"sec-map.groupby":["_ref_3","_ref_4","_ref_5"],"sec-group-by":["_ref_6","_ref_7","_ref_8","_ref_9","_ref_10","_ref_11","_ref_12","_ref_13","_ref_14","_ref_15","_ref_16","_ref_17","_ref_18"],"sec-add-value-to-keyed-group":["_ref_19"]},"entries":[{"type":"clause","id":"sec-scope","titleHTML":"Scope","number":"1"},{"type":"clause","id":"sec-object.groupby","title":"Object.groupBy ( items, callbackfn )","titleHTML":"Object.groupBy ( <var>items</var>, <var>callbackfn</var> )","number":"2.1"},{"type":"clause","id":"sec-properties-of-the-object-constructor","titleHTML":"Properties of the Object Constructor (20.1.2)","number":"2"},{"type":"clause","id":"sec-map.groupby","title":"Map.groupBy ( items, callbackfn )","titleHTML":"Map.groupBy ( <var>items</var>, <var>callbackfn</var> )","number":"3.1"},{"type":"clause","id":"sec-properties-of-the-map-constructor","titleHTML":"Properties of the Map Constructor (24.1.2)","number":"3"},{"type":"op","aoid":"GroupBy","refId":"sec-group-by"},{"type":"clause","id":"sec-group-by","title":"GroupBy ( items, callbackfn, coercion )","titleHTML":"GroupBy ( <var>items</var>, <var>callbackfn</var>, <var>coercion</var> )","number":"4.1","referencingIds":["_ref_0","_ref_3"]},{"type":"op","aoid":"AddValueToKeyedGroup","refId":"sec-add-value-to-keyed-group"},{"type":"clause","id":"sec-add-value-to-keyed-group","title":"AddValueToKeyedGroup ( groups, key, value )","titleHTML":"AddValueToKeyedGroup ( <var>groups</var>, <var>key</var>, <var>value</var> )","number":"4.2","referencingIds":["_ref_18"]},{"type":"clause","id":"sec-group-by-helpers","titleHTML":"Group By Helpers","number":"4"},{"type":"clause","id":"sec-copyright-and-software-license","title":"Copyright & Software License","titleHTML":"Copyright &amp; Software License","number":"A"}]}`);
 ;let usesMultipage = false</script><style>body {
   display: flex;
   font-size: 18px;
@@ -2414,7 +2414,7 @@
 </ul></div><div id="menu-toggle"><svg xmlns="http://www.w3.org/2000/svg" style="width:100%; height:100%; stroke:currentColor" viewBox="0 0 120 120">
       <title>Menu</title>
       <path stroke-width="10" stroke-linecap="round" d="M30,60 h60  M30,30 m0,5 h60  M30,90 m0,-5 h60"></path>
-    </svg></div><div id="menu-spacer"></div><div id="menu"><div id="menu-search"><input type="text" id="menu-search-box" placeholder="Search..."><div id="menu-search-results" class="inactive"></div></div><div id="menu-pins"><div class="menu-pane-header">Pins</div><ul id="menu-pins-list"></ul></div><div class="menu-pane-header">Table of Contents</div><div id="menu-toc"><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-scope" title="Scope"><span class="secnum">1</span> Scope</a></li><li><span class="item-toggle">◢</span><a href="#sec-properties-of-the-array-prototype-object" title="Properties of the Array Prototype Object (22.1.3)"><span class="secnum">2</span> Properties of the Array Prototype Object (22.1.3)</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-array.prototype.group" title="Array.prototype.group ( callbackfn [ , thisArg ] )"><span class="secnum">2.1</span> Array.prototype.group ( <var>callbackfn</var> [ , <var>thisArg</var> ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-array.prototype.grouptomap" title="Array.prototype.groupToMap ( callbackfn [ , thisArg ] )"><span class="secnum">2.2</span> Array.prototype.groupToMap ( <var>callbackfn</var> [ , <var>thisArg</var> ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-add-value-to-keyed-group" title="AddValueToKeyedGroup ( groups, key, value )"><span class="secnum">2.3</span> AddValueToKeyedGroup ( <var>groups</var>, <var>key</var>, <var>value</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-array.prototype-@@unscopables" title="Array.prototype [ @@unscopables ]"><span class="secnum">2.4</span> Array.prototype [ @@unscopables ]</a></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-copyright-and-software-license" title="Copyright &amp; Software License"><span class="secnum">A</span> Copyright &amp; Software License</a></li></ol></div></div><div id="spec-container"><h1 class="version">Stage 3 Draft / May 16, 2023</h1><h1 class="title">Array Grouping</h1>
+    </svg></div><div id="menu-spacer"></div><div id="menu"><div id="menu-search"><input type="text" id="menu-search-box" placeholder="Search..."><div id="menu-search-results" class="inactive"></div></div><div id="menu-pins"><div class="menu-pane-header">Pins</div><ul id="menu-pins-list"></ul></div><div class="menu-pane-header">Table of Contents</div><div id="menu-toc"><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-scope" title="Scope"><span class="secnum">1</span> Scope</a></li><li><span class="item-toggle">◢</span><a href="#sec-properties-of-the-object-constructor" title="Properties of the Object Constructor (20.1.2)"><span class="secnum">2</span> Properties of the Object Constructor (20.1.2)</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-object.groupby" title="Object.groupBy ( items, callbackfn )"><span class="secnum">2.1</span> Object.groupBy ( <var>items</var>, <var>callbackfn</var> )</a></li></ol></li><li><span class="item-toggle">◢</span><a href="#sec-properties-of-the-map-constructor" title="Properties of the Map Constructor (24.1.2)"><span class="secnum">3</span> Properties of the Map Constructor (24.1.2)</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-map.groupby" title="Map.groupBy ( items, callbackfn )"><span class="secnum">3.1</span> Map.groupBy ( <var>items</var>, <var>callbackfn</var> )</a></li></ol></li><li><span class="item-toggle">◢</span><a href="#sec-group-by-helpers" title="Group By Helpers"><span class="secnum">4</span> Group By Helpers</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-group-by" title="GroupBy ( items, callbackfn, coercion )"><span class="secnum">4.1</span> GroupBy ( <var>items</var>, <var>callbackfn</var>, <var>coercion</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-add-value-to-keyed-group" title="AddValueToKeyedGroup ( groups, key, value )"><span class="secnum">4.2</span> AddValueToKeyedGroup ( <var>groups</var>, <var>key</var>, <var>value</var> )</a></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-copyright-and-software-license" title="Copyright &amp; Software License"><span class="secnum">A</span> Copyright &amp; Software License</a></li></ol></div></div><div id="spec-container"><h1 class="version">Stage 3 Draft / May 16, 2023</h1><h1 class="title">Array Grouping</h1>
 
 <emu-clause id="sec-scope">
   <h1><span class="secnum">1</span> Scope</h1>
@@ -2423,62 +2423,58 @@ <h1><span class="secnum">1</span> Scope</h1>
   </p>
 </emu-clause>
 
-<emu-clause id="sec-properties-of-the-array-prototype-object">
-  <h1><span class="secnum">2</span> Properties of the Array Prototype Object (<a href="https://tc39.es/ecma262/#sec-properties-of-the-array-prototype-object">22.1.3</a>)</h1>
+<emu-clause id="sec-properties-of-the-object-constructor">
+  <h1><span class="secnum">2</span> Properties of the Object Constructor (<a href="https://tc39.es/ecma262/multipage/fundamental-objects.html#sec-properties-of-the-object-constructor">20.1.2</a>)</h1>
 
   <ins class="block">
-  <emu-clause id="sec-array.prototype.group">
-    <h1><span class="secnum">2.1</span> Array.prototype.group ( <var>callbackfn</var> [ , <var>thisArg</var> ] )</h1>
-    <emu-note><span class="note">Note 1</span><div class="note-contents">
-      <p><var>callbackfn</var> should be a function that accepts three arguments. <code>group</code> calls <var>callbackfn</var> once for each element in the array, in ascending order, and constructs a new object of arrays. Each value returned by <var>callbackfn</var> is coerced to a property key, and the associated element is included in the array in the constructed object according to this property key.</p>
-      <p>If a <var>thisArg</var> parameter is provided, it will be used as the <emu-val>this</emu-val> value for each invocation of <var>callbackfn</var>. If it is not provided, <emu-val>undefined</emu-val> is used instead.</p>
-      <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>group</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>group</code> is set before the first call to <var>callbackfn</var>. Elements which are appended to the array after the call to <code>group</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>group</code> visits them; elements that are deleted after the call to <code>group</code> begins and before being visited are still visited and are either looked up from the prototype or are <emu-val>undefined</emu-val>.</p>
-      <p>The return value of <code>group</code> is an object that does not inherit from <var>Object.prototype</var>.</p>
-    </div></emu-note>
-    <p>When the <code>group</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>groups</var> be a new empty <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">List</a></emu-xref>.</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>(<emu-xref href="#𝔽"><a href="https://tc39.es/ecma262/#𝔽">𝔽</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>, <emu-xref href="#𝔽"><a href="https://tc39.es/ecma262/#𝔽">𝔽</a></emu-xref>(<var>k</var>), <var>O</var> »)).</li><li>Perform <emu-xref aoid="AddValueToKeyedGroup" id="_ref_7"><a href="#sec-add-value-to-keyed-group">AddValueToKeyedGroup</a></emu-xref>(<var>groups</var>, <var>propertyKey</var>, <var>kValue</var>).</li><li>Set <var>k</var> to <var>k</var> + 1.</li></ol></li><li>Let <var>obj</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>).</li><li>For each <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]], [[Elements]] } <var>g</var> of <var>groups</var>, do<ol><li>Let <var>elements</var> be <emu-xref aoid="CreateArrayFromList" id="_ref_8"><a href="https://tc39.es/ecma262/#sec-createarrayfromlist">CreateArrayFromList</a></emu-xref>(<var>g</var>.[[Elements]]).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_9"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>obj</var>, <var>g</var>.[[Key]], <var>elements</var>).</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>group</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>
+  <emu-clause id="sec-object.groupby">
+    <h1><span class="secnum">2.1</span> Object.groupBy ( <var>items</var>, <var>callbackfn</var> )</h1>
+    <emu-note><span class="note">Note</span><div class="note-contents">
+      <p><var>callbackfn</var> should be a function that accepts two arguments. <code>groupBy</code> calls <var>callbackfn</var> once for each element in <var>items</var>, in ascending order, and constructs a new Object of arrays. Each value returned by <var>callbackfn</var> is coerced to a property key, and the associated element is included in the array in the constructed object according to this property key.</p>
+      <p><var>callbackfn</var> is called with two arguments: the value of the element and the index of the element.</p>
+      <p>The return value of <code>groupBy</code> is an object that does not inherit from %Object.prototype%.</p>
     </div></emu-note>
+    <p>When the <code>groupBy</code> method is called with two arguments, the following steps are taken:</p>
+    <emu-alg><ol><li>Let <var>groups</var> be ?&nbsp;<emu-xref aoid="GroupBy" id="_ref_0"><a href="#sec-group-by">GroupBy</a></emu-xref>(<var>items</var>, <var>callbackfn</var>, <emu-const>property</emu-const>).</li><li>Let <var>obj</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>).</li><li>For each <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]], [[Elements]] } <var>g</var> of <var>groups</var>, do<ol><li>Let <var>elements</var> be <emu-xref aoid="CreateArrayFromList" id="_ref_1"><a href="https://tc39.es/ecma262/#sec-createarrayfromlist">CreateArrayFromList</a></emu-xref>(<var>g</var>.[[Elements]]).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_2"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>obj</var>, <var>g</var>.[[Key]], <var>elements</var>).</li></ol></li><li>Return <var>obj</var>.</li></ol></emu-alg>
   </emu-clause>
   </ins>
+</emu-clause>
+
+<emu-clause id="sec-properties-of-the-map-constructor">
+  <h1><span class="secnum">3</span> Properties of the Map Constructor (<a href="https://tc39.es/ecma262/multipage/keyed-collections.html#sec-properties-of-the-map-constructor">24.1.2</a>)</h1>
 
   <ins class="block">
-  <emu-clause id="sec-array.prototype.grouptomap">
-    <h1><span class="secnum">2.2</span> Array.prototype.groupToMap ( <var>callbackfn</var> [ , <var>thisArg</var> ] )</h1>
-    <emu-note><span class="note">Note 1</span><div class="note-contents">
-      <p><var>callbackfn</var> should be a function that accepts three arguments. <code>groupToMap</code> calls <var>callbackfn</var> once for each element in the array, in ascending order, and constructs a new Map of arrays. Each value returned by <var>callbackfn</var> is used as a key in the Map, and the associated element is included in the array in the constructed Map according to this key.</p>
-      <p>If a <var>thisArg</var> parameter is provided, it will be used as the <emu-val>this</emu-val> value for each invocation of <var>callbackfn</var>. If it is not provided, <emu-val>undefined</emu-val> is used instead.</p>
-      <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>groupToMap</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>groupToMap</code> is set before the first call to <var>callbackfn</var>. Elements which are appended to the array after the call to <code>groupToMap</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>groupToMap</code> visits them; elements that are deleted after the call to <code>groupToMap</code> begins and before being visited are still visited and are either looked up from the prototype or are <emu-val>undefined</emu-val>.</p>
-      <p>The return value of <code>groupToMap</code> is a Map.</p>
-    </div></emu-note>
-    <p>When the <code>groupToMap</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_10"><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_11"><a href="https://tc39.es/ecma262/#sec-lengthofarraylike">LengthOfArrayLike</a></emu-xref>(<var>O</var>).</li><li>If <emu-xref aoid="IsCallable" id="_ref_12"><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>groups</var> be a new empty <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">List</a></emu-xref>.</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_13"><a href="https://tc39.es/ecma262/#sec-tostring">ToString</a></emu-xref>(<emu-xref href="#𝔽"><a href="https://tc39.es/ecma262/#𝔽">𝔽</a></emu-xref>(<var>k</var>)).</li><li>Let <var>kValue</var> be ?&nbsp;<emu-xref aoid="Get" id="_ref_14"><a href="https://tc39.es/ecma262/#sec-get-o-p">Get</a></emu-xref>(<var>O</var>, <var>Pk</var>).</li><li>Let <var>key</var> be ?&nbsp;<emu-xref aoid="Call" id="_ref_15"><a href="https://tc39.es/ecma262/#sec-call">Call</a></emu-xref>(<var>callbackfn</var>, <var>thisArg</var>, « <var>kValue</var>, <emu-xref href="#𝔽"><a href="https://tc39.es/ecma262/#𝔽">𝔽</a></emu-xref>(<var>k</var>), <var>O</var> »).</li><li>If <var>key</var> is <emu-val>-0</emu-val><sub>𝔽</sub>, set <var>key</var> to <emu-val>+0</emu-val><sub>𝔽</sub>.</li><li>Perform <emu-xref aoid="AddValueToKeyedGroup" id="_ref_16"><a href="#sec-add-value-to-keyed-group">AddValueToKeyedGroup</a></emu-xref>(<var>groups</var>, <var>key</var>, <var>kValue</var>).</li><li>Set <var>k</var> to <var>k</var> + 1.</li></ol></li><li>Let <var>map</var> be !&nbsp;<emu-xref aoid="Construct" id="_ref_17"><a href="https://tc39.es/ecma262/#sec-construct">Construct</a></emu-xref>(<emu-xref href="#sec-map-constructor"><a href="https://tc39.es/ecma262/#sec-map-constructor">%Map%</a></emu-xref>).</li><li>For each <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]], [[Elements]] } <var>g</var> of <var>groups</var>, do<ol><li>Let <var>elements</var> be <emu-xref aoid="CreateArrayFromList" id="_ref_18"><a href="https://tc39.es/ecma262/#sec-createarrayfromlist">CreateArrayFromList</a></emu-xref>(<var>g</var>.[[Elements]]).</li><li>Let <var>entry</var> be the <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]]: <var>g</var>.[[Key]], [[Value]]: <var>elements</var> }.</li><li>Append <var>entry</var> as the last element of <var>map</var>.[[MapData]].</li></ol></li><li>Return <var>map</var>.</li></ol></emu-alg>
-    <emu-note><span class="note">Note 2</span><div class="note-contents">
-      <p>The <code>groupToMap</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>
+  <emu-clause id="sec-map.groupby">
+    <h1><span class="secnum">3.1</span> Map.groupBy ( <var>items</var>, <var>callbackfn</var> )</h1>
+    <emu-note><span class="note">Note</span><div class="note-contents">
+      <p><var>callbackfn</var> should be a function that accepts two arguments. <code>groupBy</code> calls <var>callbackfn</var> once for each element in <var>items</var>, in ascending order, and constructs a new Map of arrays. Each value returned by <var>callbackfn</var> is used as a key in the Map, and the associated element is included in the array in the constructed Map according to this key.</p>
+      <p><var>callbackfn</var> is called with two arguments: the value of the element and the index of the element.</p>
+      <p>The return value of <code>groupBy</code> is a Map.</p>
     </div></emu-note>
+    <p>When the <code>groupBy</code> method is called with two arguments, the following steps are taken:</p>
+    <emu-alg><ol><li>Let <var>groups</var> be ?&nbsp;<emu-xref aoid="GroupBy" id="_ref_3"><a href="#sec-group-by">GroupBy</a></emu-xref>(<var>items</var>, <var>callbackfn</var>, <emu-const>zero</emu-const>).</li><li>Let <var>map</var> be !&nbsp;<emu-xref aoid="Construct" id="_ref_4"><a href="https://tc39.es/ecma262/#sec-construct">Construct</a></emu-xref>(<emu-xref href="#sec-map-constructor"><a href="https://tc39.es/ecma262/#sec-map-constructor">%Map%</a></emu-xref>).</li><li>For each <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]], [[Elements]] } <var>g</var> of <var>groups</var>, do<ol><li>Let <var>elements</var> be <emu-xref aoid="CreateArrayFromList" id="_ref_5"><a href="https://tc39.es/ecma262/#sec-createarrayfromlist">CreateArrayFromList</a></emu-xref>(<var>g</var>.[[Elements]]).</li><li>Let <var>entry</var> be the <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]]: <var>g</var>.[[Key]], [[Value]]: <var>elements</var> }.</li><li>Append <var>entry</var> as the last element of <var>map</var>.[[MapData]].</li></ol></li><li>Return <var>map</var>.</li></ol></emu-alg>
+  </emu-clause>
+  </ins>
+</emu-clause>
+
+<emu-clause id="sec-group-by-helpers">
+  <h1><span class="secnum">4</span> Group By Helpers</h1>
+
+  <ins class="block">
+  <emu-clause id="sec-group-by" type="abstract operation" aoid="GroupBy">
+    <h1><span class="secnum">4.1</span> GroupBy ( <var>items</var>, <var>callbackfn</var>, <var>coercion</var> )</h1>
+    <p>The abstract operation GroupBy takes arguments <var>items</var> (an <emu-xref href="#sec-ecmascript-language-types"><a href="https://tc39.es/ecma262/#sec-ecmascript-language-types">ECMAScript language value</a></emu-xref>), <var>callbackfn</var> (an <emu-xref href="#sec-ecmascript-language-types"><a href="https://tc39.es/ecma262/#sec-ecmascript-language-types">ECMAScript language value</a></emu-xref>), and <var>coercion</var> (<emu-const>property</emu-const> or <emu-const>zero</emu-const>) and returns either a normal completion containing a <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">List</a></emu-xref> of Records with fields [[Key]] (an <emu-xref href="#sec-ecmascript-language-types"><a href="https://tc39.es/ecma262/#sec-ecmascript-language-types">ECMAScript language value</a></emu-xref>) and [[Elements]] (a <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">List</a></emu-xref> of ECMAScript language values), or a throw completion. It performs the following steps when called:</p>
+    <emu-alg><ol><li>Perform ?&nbsp;<emu-xref aoid="RequireObjectCoercible" id="_ref_6"><a href="https://tc39.es/ecma262/#sec-requireobjectcoercible">RequireObjectCoercible</a></emu-xref>(<var>items</var>).</li><li>If <emu-xref aoid="IsCallable" id="_ref_7"><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>groups</var> be a new empty <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">List</a></emu-xref>.</li><li>Let <var>iteratorRecord</var> be ?&nbsp;<emu-xref aoid="GetIterator" id="_ref_8"><a href="https://tc39.es/ecma262/#sec-getiterator">GetIterator</a></emu-xref>(<var>items</var>).</li><li>Let <var>k</var> be 0.</li><li>Repeat,<ol><li>If <var>k</var> ≥ 2<sup>53</sup> - 1, then<ol><li>Let <var>error</var> be <emu-xref aoid="ThrowCompletion" id="_ref_9"><a href="https://tc39.es/ecma262/#sec-throwcompletion">ThrowCompletion</a></emu-xref>(a newly created <emu-val>TypeError</emu-val> object).</li><li>Return ?&nbsp;<emu-xref aoid="IteratorClose" id="_ref_10"><a href="https://tc39.es/ecma262/#sec-iteratorclose">IteratorClose</a></emu-xref>(<var>iteratorRecord</var>, <var>error</var>).</li></ol></li><li>Let <var>Pk</var> be !&nbsp;<emu-xref aoid="ToString" id="_ref_11"><a href="https://tc39.es/ecma262/#sec-tostring">ToString</a></emu-xref>(<emu-xref href="#𝔽"><a href="https://tc39.es/ecma262/#𝔽">𝔽</a></emu-xref>(<var>k</var>)).</li><li>Let <var>next</var> be ?&nbsp;<emu-xref aoid="IteratorStep" id="_ref_12"><a href="https://tc39.es/ecma262/#sec-iteratorstep">IteratorStep</a></emu-xref>(<var>iteratorRecord</var>).</li><li>If <var>next</var> is <emu-val>false</emu-val>, then<ol><li>Return <var>groups</var>.</li></ol></li><li>Let <var>value</var> be ?&nbsp;<emu-xref aoid="IteratorValue" id="_ref_13"><a href="https://tc39.es/ecma262/#sec-iteratorvalue">IteratorValue</a></emu-xref>(<var>next</var>).</li><li>Let <var>key</var> be <emu-xref aoid="Completion" id="_ref_14"><a href="https://tc39.es/ecma262/#sec-completion-record-specification-type">Completion</a></emu-xref>(<emu-xref aoid="Call" id="_ref_15"><a href="https://tc39.es/ecma262/#sec-call">Call</a></emu-xref>(<var>callbackfn</var>, <emu-val>undefined</emu-val>, « <var>value</var>, <emu-xref href="#𝔽"><a href="https://tc39.es/ecma262/#𝔽">𝔽</a></emu-xref>(<var>k</var>) »)).</li><li>IfAbruptCloseIterator(<var>key</var>, <var>iteratorRecord</var>).</li><li>If <var>coercion</var> is <emu-const>property</emu-const>, then<ol><li>Set <var>key</var> to <emu-xref aoid="Completion" id="_ref_16"><a href="https://tc39.es/ecma262/#sec-completion-record-specification-type">Completion</a></emu-xref>(<emu-xref aoid="ToPropertyKey" id="_ref_17"><a href="https://tc39.es/ecma262/#sec-topropertykey">ToPropertyKey</a></emu-xref>(<var>key</var>)).</li><li>IfAbruptCloseIterator(<var>key</var>, <var>iteratorRecord</var>).</li></ol></li><li>Else,<ol><li><emu-xref href="#assert"><a href="https://tc39.es/ecma262/#assert">Assert</a></emu-xref>: <var>coercion</var> is <emu-const>zero</emu-const>.</li><li>If <var>key</var> is <emu-val>-0</emu-val><sub>𝔽</sub>, set <var>key</var> to <emu-val>+0</emu-val><sub>𝔽</sub>.</li></ol></li><li>Perform <emu-xref aoid="AddValueToKeyedGroup" id="_ref_18"><a href="#sec-add-value-to-keyed-group">AddValueToKeyedGroup</a></emu-xref>(<var>groups</var>, <var>key</var>, <var>value</var>).</li><li>Set <var>k</var> to <var>k</var> + 1.</li></ol></li></ol></emu-alg>
   </emu-clause>
+  </ins>
 
+  <ins class="block">
   <emu-clause id="sec-add-value-to-keyed-group" type="abstract operation" aoid="AddValueToKeyedGroup">
-    <h1><span class="secnum">2.3</span> AddValueToKeyedGroup ( <var>groups</var>, <var>key</var>, <var>value</var> )</h1>
+    <h1><span class="secnum">4.2</span> AddValueToKeyedGroup ( <var>groups</var>, <var>key</var>, <var>value</var> )</h1>
     <p>The abstract operation AddValueToKeyedGroup takes arguments <var>groups</var> (a <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">List</a></emu-xref> of Records that have [[Key]] and [[Elements]] fields), <var>key</var> (an <emu-xref href="#sec-ecmascript-language-types"><a href="https://tc39.es/ecma262/#sec-ecmascript-language-types">ECMAScript language value</a></emu-xref>), and <var>value</var> (an <emu-xref href="#sec-ecmascript-language-types"><a href="https://tc39.es/ecma262/#sec-ecmascript-language-types">ECMAScript language value</a></emu-xref>) and returns <emu-const>unused</emu-const>. It performs the following steps when called:</p>
     <emu-alg><ol><li>For each <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]], [[Elements]] } <var>g</var> of <var>groups</var>, do<ol><li>If <emu-xref aoid="SameValue" id="_ref_19"><a href="https://tc39.es/ecma262/#sec-samevalue">SameValue</a></emu-xref>(<var>g</var>.[[Key]], <var>key</var>) is <emu-val>true</emu-val>, then<ol><li><emu-xref href="#assert"><a href="https://tc39.es/ecma262/#assert">Assert</a></emu-xref>: exactly one element of <var>groups</var> meets this criteria.</li><li>Append <var>value</var> as the last element of <var>g</var>.[[Elements]].</li><li>Return <emu-const>unused</emu-const>.</li></ol></li></ol></li><li>Let <var>group</var> be the <emu-xref href="#sec-list-and-record-specification-type"><a href="https://tc39.es/ecma262/#sec-list-and-record-specification-type">Record</a></emu-xref> { [[Key]]: <var>key</var>, [[Elements]]: « <var>value</var> » }.</li><li>Append <var>group</var> as the last element of <var>groups</var>.</li><li>Return <emu-const>unused</emu-const>.</li></ol></emu-alg>
   </emu-clause>
   </ins>
-
-  <emu-clause id="sec-array.prototype-@@unscopables">
-    <h1><span class="secnum">2.4</span> Array.prototype [ @@unscopables ]</h1>
-    <p>The initial value of the @@unscopables <emu-xref href="#sec-object-type"><a href="https://tc39.es/ecma262/#sec-object-type">data property</a></emu-xref> is an object created by the following steps:</p>
-    <emu-alg><ol><li>Let <var>unscopableList</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_20"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"at"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_21"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"copyWithin"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_22"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"entries"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_23"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"fill"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_24"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"find"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_25"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"findIndex"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_26"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"flat"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_27"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"flatMap"</emu-val>, <emu-val>true</emu-val>).</li><li><ins>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_28"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"group"</emu-val>, <emu-val>true</emu-val>).</ins></li><li><ins>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_29"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"groupToMap"</emu-val>, <emu-val>true</emu-val>).</ins></li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_30"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"includes"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_31"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"keys"</emu-val>, <emu-val>true</emu-val>).</li><li>Perform !&nbsp;<emu-xref aoid="CreateDataPropertyOrThrow" id="_ref_32"><a href="https://tc39.es/ecma262/#sec-createdatapropertyorthrow">CreateDataPropertyOrThrow</a></emu-xref>(<var>unscopableList</var>, <emu-val>"values"</emu-val>, <emu-val>true</emu-val>).</li><li>Return <var>unscopableList</var>.</li></ol></emu-alg>
-    <p>This property has the attributes { [[Writable]]: <emu-val>false</emu-val>, [[Enumerable]]: <emu-val>false</emu-val>, [[Configurable]]: <emu-val>true</emu-val> }.</p>
-    <emu-note><span class="note">Note</span><div class="note-contents">
-      <p>The own property names of this object are property names that were not included as standard properties of <code>Array.prototype</code> prior to the ECMAScript 2015 specification. These names are ignored for <code>with</code> statement binding purposes in order to preserve the behaviour of existing code that might use one of these names as a binding in an outer scope that is shadowed by a <code>with</code> statement whose binding object is an Array.</p>
-    </div></emu-note>
-  </emu-clause>
 </emu-clause><emu-annex id="sec-copyright-and-software-license">
       <h1><span class="secnum">A</span> Copyright &amp; Software License</h1>
       
diff --git a/spec.emu b/spec.emu
index 5277c21..cf4ee35 100644
--- a/spec.emu
+++ b/spec.emu
@@ -18,70 +18,44 @@ location: https://tc39.es/proposal-array-grouping/
   </p>
 </emu-clause>
 
-<emu-clause id="sec-properties-of-the-array-prototype-object">
-  <h1>Properties of the Array Prototype Object (<a href="https://tc39.es/ecma262/#sec-properties-of-the-array-prototype-object">22.1.3</a>)</h1>
+<emu-clause id="sec-properties-of-the-object-constructor">
+  <h1>Properties of the Object Constructor (<a href="https://tc39.es/ecma262/multipage/fundamental-objects.html#sec-properties-of-the-object-constructor">20.1.2</a>)</h1>
 
   <ins class="block">
-  <emu-clause id="sec-array.prototype.group">
-    <h1>Array.prototype.group ( _callbackfn_ [ , _thisArg_ ] )</h1>
+  <emu-clause id="sec-object.groupby">
+    <h1>Object.groupBy ( _items_, _callbackfn_ )</h1>
     <emu-note>
-      <p>_callbackfn_ should be a function that accepts three arguments. `group` calls _callbackfn_ once for each element in the array, in ascending order, and constructs a new object of arrays. Each value returned by _callbackfn_ is coerced to a property key, and the associated element is included in the array in the constructed object according to this property key.</p>
-      <p>If a _thisArg_ parameter is provided, it will be used as the *this* value for each invocation of _callbackfn_. If it is not provided, *undefined* is used instead.</p>
-      <p>_callbackfn_ is called with three arguments: the value of the element, the index of the element, and the object being traversed.</p>
-      <p>`group` 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 `group` is set before the first call to _callbackfn_. Elements which are appended to the array after the call to `group` 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 `group` visits them; elements that are deleted after the call to `group` begins and before being visited are still visited and are either looked up from the prototype or are *undefined*.</p>
-      <p>The return value of `group` is an object that does not inherit from _Object.prototype_.</p>
+      <p>_callbackfn_ should be a function that accepts two arguments. `groupBy` calls _callbackfn_ once for each element in _items_, in ascending order, and constructs a new Object of arrays. Each value returned by _callbackfn_ is coerced to a property key, and the associated element is included in the array in the constructed object according to this property key.</p>
+      <p>_callbackfn_ is called with two arguments: the value of the element and the index of the element.</p>
+      <p>The return value of `groupBy` is an object that does not inherit from %Object.prototype%.</p>
     </emu-note>
-    <p>When the `group` method is called with one or two arguments, the following steps are taken:</p>
+    <p>When the `groupBy` method is called with 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 _groups_ be a new empty List.
-      1. Repeat, while _k_ &lt; _len_
-        1. Let _Pk_ be ! ToString(𝔽(_k_)).
-        1. Let _kValue_ be ? Get(_O_, _Pk_).
-        1. Let _propertyKey_ be ? ToPropertyKey(? Call(_callbackfn_, _thisArg_, &laquo; _kValue_, 𝔽(_k_), _O_ &raquo;)).
-        1. Perform AddValueToKeyedGroup(_groups_, _propertyKey_, _kValue_).
-        1. Set _k_ to _k_ + 1.
+      1. Let _groups_ be ? GroupBy(_items_, _callbackfn_, ~property~).
       1. Let _obj_ be OrdinaryObjectCreate(*null*).
       1. For each Record { [[Key]], [[Elements]] } _g_ of _groups_, do
         1. Let _elements_ be CreateArrayFromList(_g_.[[Elements]]).
         1. Perform ! CreateDataPropertyOrThrow(_obj_, _g_.[[Key]], _elements_).
       1. Return _obj_.
     </emu-alg>
-    <emu-note>
-      <p>The `group` function is intentionally generic; it does not require that its *this* value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.</p>
-    </emu-note>
   </emu-clause>
   </ins>
+</emu-clause>
+
+<emu-clause id="sec-properties-of-the-map-constructor">
+  <h1>Properties of the Map Constructor (<a href="https://tc39.es/ecma262/multipage/keyed-collections.html#sec-properties-of-the-map-constructor">24.1.2</a>)</h1>
 
   <ins class="block">
-  <emu-clause id="sec-array.prototype.grouptomap">
-    <h1>Array.prototype.groupToMap ( _callbackfn_ [ , _thisArg_ ] )</h1>
+  <emu-clause id="sec-map.groupby">
+    <h1>Map.groupBy ( _items_, _callbackfn_ )</h1>
     <emu-note>
-      <p>_callbackfn_ should be a function that accepts three arguments. `groupToMap` calls _callbackfn_ once for each element in the array, in ascending order, and constructs a new Map of arrays. Each value returned by _callbackfn_ is used as a key in the Map, and the associated element is included in the array in the constructed Map according to this key.</p>
-      <p>If a _thisArg_ parameter is provided, it will be used as the *this* value for each invocation of _callbackfn_. If it is not provided, *undefined* is used instead.</p>
-      <p>_callbackfn_ is called with three arguments: the value of the element, the index of the element, and the object being traversed.</p>
-      <p>`groupToMap` 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 `groupToMap` is set before the first call to _callbackfn_. Elements which are appended to the array after the call to `groupToMap` 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 `groupToMap` visits them; elements that are deleted after the call to `groupToMap` begins and before being visited are still visited and are either looked up from the prototype or are *undefined*.</p>
-      <p>The return value of `groupToMap` is a Map.</p>
+      <p>_callbackfn_ should be a function that accepts two arguments. `groupBy` calls _callbackfn_ once for each element in _items_, in ascending order, and constructs a new Map of arrays. Each value returned by _callbackfn_ is used as a key in the Map, and the associated element is included in the array in the constructed Map according to this key.</p>
+      <p>_callbackfn_ is called with two arguments: the value of the element and the index of the element.</p>
+      <p>The return value of `groupBy` is a Map.</p>
     </emu-note>
-    <p>When the `groupToMap` method is called with one or two arguments, the following steps are taken:</p>
+    <p>When the `groupBy` method is called with 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 _groups_ be a new empty List.
-      1. Repeat, while _k_ &lt; _len_
-        1. Let _Pk_ be ! ToString(𝔽(_k_)).
-        1. Let _kValue_ be ? Get(_O_, _Pk_).
-        1. Let _key_ be ? Call(_callbackfn_, _thisArg_, &laquo; _kValue_, 𝔽(_k_), _O_ &raquo;).
-        1. If _key_ is *-0*<sub>𝔽</sub>, set _key_ to *+0*<sub>𝔽</sub>.
-        1. Perform AddValueToKeyedGroup(_groups_, _key_, _kValue_).
-        1. Set _k_ to _k_ + 1.
+      1. Let _groups_ be ? GroupBy(_items_, _callbackfn_, ~zero~).
       1. Let _map_ be ! Construct(%Map%).
       1. For each Record { [[Key]], [[Elements]] } _g_ of _groups_, do
         1. Let _elements_ be CreateArrayFromList(_g_.[[Elements]]).
@@ -89,11 +63,54 @@ location: https://tc39.es/proposal-array-grouping/
         1. Append _entry_ as the last element of _map_.[[MapData]].
       1. Return _map_.
     </emu-alg>
-    <emu-note>
-      <p>The `groupToMap` function is intentionally generic; it does not require that its *this* value be an Array object. Therefore it can be transferred to other kinds of objects for use as a method.</p>
-    </emu-note>
   </emu-clause>
+  </ins>
+</emu-clause>
+
+<emu-clause id="sec-group-by-helpers">
+  <h1>Group By Helpers</h1>
+
+  <ins class="block">
+  <emu-clause id="sec-group-by" type="abstract operation">
+    <h1>
+      GroupBy (
+        _items_: an ECMAScript language value,
+        _callbackfn_: an ECMAScript language value,
+        _coercion_: ~property~ or ~zero~,
+      ): either a normal completion containing a List of Records with fields [[Key]] (an ECMAScript language value) and [[Elements]] (a List of ECMAScript language values), or a throw completion
+    </h1>
+    <dl class="header">
+    </dl>
+    <emu-alg>
+      1. Perform ? RequireObjectCoercible(_items_).
+      1. If IsCallable(_callbackfn_) is *false*, throw a *TypeError* exception.
+      1. Let _groups_ be a new empty List.
+      1. Let _iteratorRecord_ be ? GetIterator(_items_).
+      1. Let _k_ be 0.
+      1. Repeat,
+        1. If _k_ ≥ 2<sup>53</sup> - 1, then
+          1. Let _error_ be ThrowCompletion(a newly created *TypeError* object).
+          1. Return ? IteratorClose(_iteratorRecord_, _error_).
+        1. Let _Pk_ be ! ToString(𝔽(_k_)).
+        1. Let _next_ be ? IteratorStep(_iteratorRecord_).
+        1. If _next_ is *false*, then
+          1. Return _groups_.
+        1. Let _value_ be ? IteratorValue(_next_).
+        1. Let _key_ be Completion(Call(_callbackfn_, *undefined*, &laquo; _value_, 𝔽(_k_) &raquo;)).
+        1. IfAbruptCloseIterator(_key_, _iteratorRecord_).
+        1. If _coercion_ is ~property~, then
+          1. Set _key_ to Completion(ToPropertyKey(_key_)).
+          1. IfAbruptCloseIterator(_key_, _iteratorRecord_).
+        1. Else,
+          1. Assert: _coercion_ is ~zero~.
+          1. If _key_ is *-0*<sub>𝔽</sub>, set _key_ to *+0*<sub>𝔽</sub>.
+        1. Perform AddValueToKeyedGroup(_groups_, _key_, _value_).
+        1. Set _k_ to _k_ + 1.
+    </emu-alg>
+  </emu-clause>
+  </ins>
 
+  <ins class="block">
   <emu-clause id="sec-add-value-to-keyed-group" type="abstract operation">
     <h1>
       AddValueToKeyedGroup (
@@ -105,41 +122,15 @@ location: https://tc39.es/proposal-array-grouping/
     <dl class="header">
     </dl>
     <emu-alg>
-        1. For each Record { [[Key]], [[Elements]] } _g_ of _groups_, do
-          1. If SameValue(_g_.[[Key]], _key_) is *true*, then
-            1. Assert: exactly one element of _groups_ meets this criteria.
-            1. Append _value_ as the last element of _g_.[[Elements]].
-            1. Return ~unused~.
-        1. Let _group_ be the Record { [[Key]]: _key_, [[Elements]]: &laquo; _value_ &raquo; }.
-        1. Append _group_ as the last element of _groups_.
-        1. Return ~unused~.
+      1. For each Record { [[Key]], [[Elements]] } _g_ of _groups_, do
+        1. If SameValue(_g_.[[Key]], _key_) is *true*, then
+          1. Assert: exactly one element of _groups_ meets this criteria.
+          1. Append _value_ as the last element of _g_.[[Elements]].
+          1. Return ~unused~.
+      1. Let _group_ be the Record { [[Key]]: _key_, [[Elements]]: &laquo; _value_ &raquo; }.
+      1. Append _group_ as the last element of _groups_.
+      1. Return ~unused~.
     </emu-alg>
   </emu-clause>
   </ins>
-
-  <emu-clause id="sec-array.prototype-@@unscopables">
-    <h1>Array.prototype [ @@unscopables ]</h1>
-    <p>The initial value of the @@unscopables data property is an object created by the following steps:</p>
-    <emu-alg>
-      1. Let _unscopableList_ be OrdinaryObjectCreate(*null*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"at"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"copyWithin"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"entries"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"fill"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"find"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"findIndex"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"flat"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"flatMap"*, *true*).
-      1. <ins>Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"group"*, *true*).</ins>
-      1. <ins>Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"groupToMap"*, *true*).</ins>
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"includes"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"keys"*, *true*).
-      1. Perform ! CreateDataPropertyOrThrow(_unscopableList_, *"values"*, *true*).
-      1. Return _unscopableList_.
-    </emu-alg>
-    <p>This property has the attributes { [[Writable]]: *false*, [[Enumerable]]: *false*, [[Configurable]]: *true* }.</p>
-    <emu-note>
-      <p>The own property names of this object are property names that were not included as standard properties of `Array.prototype` prior to the ECMAScript 2015 specification. These names are ignored for `with` statement binding purposes in order to preserve the behaviour of existing code that might use one of these names as a binding in an outer scope that is shadowed by a `with` statement whose binding object is an Array.</p>
-    </emu-note>
-  </emu-clause>
 </emu-clause>