From f75b286992f485f5ccdc8b56d598a70dc47884b5 Mon Sep 17 00:00:00 2001
From: Dominic Farolino <domfarolino@gmail.com>
Date: Tue, 23 Apr 2024 19:16:40 +0000
Subject: [PATCH] Fix predicate. Fix #140. (#141)

SHA: b4b9d4327bc6e623bb9be19cc85bbcf0e8382447
Reason: push, by domfarolino

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 index.html | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/index.html b/index.html
index b902110..e705186 100644
--- a/index.html
+++ b/index.html
@@ -6,7 +6,7 @@
   <link href="https://www.w3.org/StyleSheets/TR/2021/cg-draft" rel="stylesheet">
   <meta content="Bikeshed version 82ce88815, updated Thu Sep 7 16:33:55 2023 -0700" name="generator">
   <link href="https://wicg.github.io/observable/" rel="canonical">
-  <meta content="5fac9fd6cfaf594df97f4fbe2b09597e0725a7e1" name="document-revision">
+  <meta content="b4b9d4327bc6e623bb9be19cc85bbcf0e8382447" name="document-revision">
 <style>
 /* Put nice boxes around each algorithm. */
 [data-algorithm]:not(.heading) {
@@ -901,7 +901,7 @@
   <div class="head">
    <p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2021/logos/W3C" width="72"> </a> </p>
    <h1 class="p-name no-ref" id="title">Observable</h1>
-   <p id="w3c-state"><a href="https://www.w3.org/standards/types#CG-DRAFT">Draft Community Group Report</a>, <time class="dt-updated" datetime="2024-04-03">3 April 2024</time></p>
+   <p id="w3c-state"><a href="https://www.w3.org/standards/types#CG-DRAFT">Draft Community Group Report</a>, <time class="dt-updated" datetime="2024-04-23">23 April 2024</time></p>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>This version:
@@ -1137,12 +1137,12 @@ <h3 class="heading settled" data-level="2.2" id="observable-api"><span class="se
   <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#abortsignal" id="ref-for-abortsignal②"><c- n>AbortSignal</c-></a> <dfn class="dfn-paneled idl-code" data-dfn-for="SubscribeOptions" data-dfn-type="dict-member" data-export data-type="AbortSignal " id="dom-subscribeoptions-signal"><code><c- g>signal</c-></code></dfn>;
 };
 
-<c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-predicate"><code><c- g>Predicate</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean①"><c- b>boolean</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any③"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Predicate" data-dfn-type="argument" data-export id="dom-predicate-value"><code><c- g>value</c-></code><a class="self-link" href="#dom-predicate-value"></a></dfn>);
+<c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-predicate"><code><c- g>Predicate</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean" id="ref-for-idl-boolean①"><c- b>boolean</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any③"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Predicate" data-dfn-type="argument" data-export id="dom-predicate-value"><code><c- g>value</c-></code><a class="self-link" href="#dom-predicate-value"></a></dfn>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Predicate" data-dfn-type="argument" data-export id="dom-predicate-index"><code><c- g>index</c-></code><a class="self-link" href="#dom-predicate-index"></a></dfn>);
 <c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-reducer"><code><c- g>Reducer</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any④"><c- b>any</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑤"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Reducer" data-dfn-type="argument" data-export id="dom-reducer-accumulator"><code><c- g>accumulator</c-></code><a class="self-link" href="#dom-reducer-accumulator"></a></dfn>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑥"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Reducer" data-dfn-type="argument" data-export id="dom-reducer-currentvalue"><code><c- g>currentValue</c-></code><a class="self-link" href="#dom-reducer-currentvalue"></a></dfn>);
-<c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-mapper"><code><c- g>Mapper</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑦"><c- b>any</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑧"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Mapper" data-dfn-type="argument" data-export id="dom-mapper-element"><code><c- g>element</c-></code><a class="self-link" href="#dom-mapper-element"></a></dfn>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Mapper" data-dfn-type="argument" data-export id="dom-mapper-index"><code><c- g>index</c-></code><a class="self-link" href="#dom-mapper-index"></a></dfn>);
+<c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-mapper"><code><c- g>Mapper</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑦"><c- b>any</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑧"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Mapper" data-dfn-type="argument" data-export id="dom-mapper-element"><code><c- g>element</c-></code><a class="self-link" href="#dom-mapper-element"></a></dfn>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long①"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Mapper" data-dfn-type="argument" data-export id="dom-mapper-index"><code><c- g>index</c-></code><a class="self-link" href="#dom-mapper-index"></a></dfn>);
 // Differs from Mapper only in return type, since this callback is exclusively
 // used to visit each element in a sequence, not transform it.
-<c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-visitor"><code><c- g>Visitor</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-undefined" id="ref-for-idl-undefined⑥"><c- b>undefined</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑨"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Visitor" data-dfn-type="argument" data-export id="dom-visitor-element"><code><c- g>element</c-></code><a class="self-link" href="#dom-visitor-element"></a></dfn>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long①"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Visitor" data-dfn-type="argument" data-export id="dom-visitor-index"><code><c- g>index</c-></code><a class="self-link" href="#dom-visitor-index"></a></dfn>);
+<c- b>callback</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="callback" data-export id="callbackdef-visitor"><code><c- g>Visitor</c-></code></dfn> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-undefined" id="ref-for-idl-undefined⑥"><c- b>undefined</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any⑨"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Visitor" data-dfn-type="argument" data-export id="dom-visitor-element"><code><c- g>element</c-></code><a class="self-link" href="#dom-visitor-element"></a></dfn>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long②"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Visitor" data-dfn-type="argument" data-export id="dom-visitor-index"><code><c- g>index</c-></code><a class="self-link" href="#dom-visitor-index"></a></dfn>);
 
 [Exposed=*]
 <c- b>interface</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="interface" data-export id="observable"><code><c- g>Observable</c-></code></dfn> {
@@ -1163,8 +1163,8 @@ <h3 class="heading settled" data-level="2.2" id="observable-api"><span class="se
   <a data-link-type="idl-name" href="#observable" id="ref-for-observable②"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-takeuntil" id="ref-for-dom-observable-takeuntil"><c- g>takeUntil</c-></a>(<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any" id="ref-for-idl-any①①"><c- b>any</c-></a> <dfn class="idl-code" data-dfn-for="Observable/takeUntil(notifier)" data-dfn-type="argument" data-export id="dom-observable-takeuntil-notifier-notifier"><code><c- g>notifier</c-></code><a class="self-link" href="#dom-observable-takeuntil-notifier-notifier"></a></dfn>);
   <a data-link-type="idl-name" href="#observable" id="ref-for-observable③"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-map" id="ref-for-dom-observable-map"><c- g>map</c-></a>(<a data-link-type="idl-name" href="#callbackdef-mapper" id="ref-for-callbackdef-mapper"><c- n>Mapper</c-></a> <dfn class="idl-code" data-dfn-for="Observable/map(mapper)" data-dfn-type="argument" data-export id="dom-observable-map-mapper-mapper"><code><c- g>mapper</c-></code><a class="self-link" href="#dom-observable-map-mapper-mapper"></a></dfn>);
   <a data-link-type="idl-name" href="#observable" id="ref-for-observable④"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-filter" id="ref-for-dom-observable-filter"><c- g>filter</c-></a>(<a data-link-type="idl-name" href="#callbackdef-predicate" id="ref-for-callbackdef-predicate"><c- n>Predicate</c-></a> <dfn class="idl-code" data-dfn-for="Observable/filter(predicate)" data-dfn-type="argument" data-export id="dom-observable-filter-predicate-predicate"><code><c- g>predicate</c-></code><a class="self-link" href="#dom-observable-filter-predicate-predicate"></a></dfn>);
-  <a data-link-type="idl-name" href="#observable" id="ref-for-observable⑤"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-take" id="ref-for-dom-observable-take"><c- g>take</c-></a>(<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long②"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Observable/take(amount)" data-dfn-type="argument" data-export id="dom-observable-take-amount-amount"><code><c- g>amount</c-></code><a class="self-link" href="#dom-observable-take-amount-amount"></a></dfn>);
-  <a data-link-type="idl-name" href="#observable" id="ref-for-observable⑥"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-drop" id="ref-for-dom-observable-drop"><c- g>drop</c-></a>(<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long③"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Observable/drop(amount)" data-dfn-type="argument" data-export id="dom-observable-drop-amount-amount"><code><c- g>amount</c-></code><a class="self-link" href="#dom-observable-drop-amount-amount"></a></dfn>);
+  <a data-link-type="idl-name" href="#observable" id="ref-for-observable⑤"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-take" id="ref-for-dom-observable-take"><c- g>take</c-></a>(<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long③"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Observable/take(amount)" data-dfn-type="argument" data-export id="dom-observable-take-amount-amount"><code><c- g>amount</c-></code><a class="self-link" href="#dom-observable-take-amount-amount"></a></dfn>);
+  <a data-link-type="idl-name" href="#observable" id="ref-for-observable⑥"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-drop" id="ref-for-dom-observable-drop"><c- g>drop</c-></a>(<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long④"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <dfn class="idl-code" data-dfn-for="Observable/drop(amount)" data-dfn-type="argument" data-export id="dom-observable-drop-amount-amount"><code><c- g>amount</c-></code><a class="self-link" href="#dom-observable-drop-amount-amount"></a></dfn>);
   <a data-link-type="idl-name" href="#observable" id="ref-for-observable⑦"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-flatmap" id="ref-for-dom-observable-flatmap"><c- g>flatMap</c-></a>(<a data-link-type="idl-name" href="#callbackdef-mapper" id="ref-for-callbackdef-mapper①"><c- n>Mapper</c-></a> <dfn class="idl-code" data-dfn-for="Observable/flatMap(mapper)" data-dfn-type="argument" data-export id="dom-observable-flatmap-mapper-mapper"><code><c- g>mapper</c-></code><a class="self-link" href="#dom-observable-flatmap-mapper-mapper"></a></dfn>);
   <a data-link-type="idl-name" href="#observable" id="ref-for-observable⑧"><c- n>Observable</c-></a> <a class="idl-code" data-link-type="method" href="#dom-observable-finally" id="ref-for-dom-observable-finally"><c- g>finally</c-></a>(<a data-link-type="idl-name" href="https://webidl.spec.whatwg.org/#VoidFunction" id="ref-for-VoidFunction③"><c- n>VoidFunction</c-></a> <dfn class="idl-code" data-dfn-for="Observable/finally(callback)" data-dfn-type="argument" data-export id="dom-observable-finally-callback-callback"><code><c- g>callback</c-></code><a class="self-link" href="#dom-observable-finally-callback-callback"></a></dfn>);
 
@@ -1440,7 +1440,7 @@ <h4 class="heading settled" data-level="2.3.2" id="observable-returning-operator
  algorithm that takes a <code class="idl"><a data-link-type="idl" href="#subscriber" id="ref-for-subscriber①⑤">Subscriber</a></code> <var>subscriber</var> and does the following:</p>
       <ol>
        <li data-md>
-        <p>Let <var>idx</var> be an <code class="idl"><a data-link-type="idl" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long④">unsigned long long</a></code>, initially 0.</p>
+        <p>Let <var>idx</var> be an <code class="idl"><a data-link-type="idl" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long⑤">unsigned long long</a></code>, initially 0.</p>
        <li data-md>
         <p>Let <var>sourceObserver</var> be a new <a data-link-type="dfn" href="#internal-observer" id="ref-for-internal-observer⑥">internal observer</a>, initialized as follows:</p>
         <dl>
@@ -1489,6 +1489,8 @@ <h4 class="heading settled" data-level="2.3.2" id="observable-returning-operator
       <p>Let <var>observable</var> be a <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#new" id="ref-for-new③">new</a> <code class="idl"><a data-link-type="idl" href="#observable" id="ref-for-observable②③">Observable</a></code> whose <a data-link-type="dfn" href="#observable-subscribe-callback" id="ref-for-observable-subscribe-callback⑦">subscribe callback</a> is an
  algorithm that takes a <code class="idl"><a data-link-type="idl" href="#subscriber" id="ref-for-subscriber①⑥">Subscriber</a></code> <var>subscriber</var> and does the following:</p>
       <ol>
+       <li data-md>
+        <p>Let <var>idx</var> be an <code class="idl"><a data-link-type="idl" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long⑥">unsigned long long</a></code>, initially 0.</p>
        <li data-md>
         <p>Let <var>sourceObserver</var> be a new <a data-link-type="dfn" href="#internal-observer" id="ref-for-internal-observer⑦">internal observer</a>, initialized as follows:</p>
         <dl>
@@ -1496,10 +1498,13 @@ <h4 class="heading settled" data-level="2.3.2" id="observable-returning-operator
          <dd data-md>
           <ol>
            <li data-md>
-            <p><a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#invoke-a-callback-function" id="ref-for-invoke-a-callback-function①⓪">Invoke</a> <var>predicate</var> with the passed in <var>value</var>, and let <var>matches</var> be the returned value.</p>
+            <p><a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#invoke-a-callback-function" id="ref-for-invoke-a-callback-function①⓪">Invoke</a> <var>predicate</var> with the passed in <var>value</var> and <var>idx</var>, and let <var>matches</var> be
+  the returned value.</p>
             <p>If <a data-link-type="dfn" href="https://webidl.spec.whatwg.org/#an-exception-was-thrown" id="ref-for-an-exception-was-thrown①①">an exception <var>E</var> was thrown</a>,
   then run <var>subscriber</var>’s <code class="idl"><a data-link-type="idl" href="#dom-subscriber-error" id="ref-for-dom-subscriber-error⑦">error()</a></code> method, given <var>E</var>, and abort these
   steps.</p>
+           <li data-md>
+            <p>Set <var>idx</var> to <var>idx</var> + 1.</p>
            <li data-md>
             <p>If <var>matches</var> is true, then run <var>subscriber</var>’s <code class="idl"><a data-link-type="idl" href="#dom-subscriber-next" id="ref-for-dom-subscriber-next⑤">next()</a></code> method, given <var>value</var>.</p>
           </ol>
@@ -1843,7 +1848,7 @@ <h4 class="heading settled" data-level="2.3.3" id="promise-returning-operators">
   rejection handler runs.</p>
       </ol>
      <li data-md>
-      <p>Let <var>idx</var> be an <code class="idl"><a data-link-type="idl" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long⑤">unsigned long long</a></code>, initially 0.</p>
+      <p>Let <var>idx</var> be an <code class="idl"><a data-link-type="idl" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long" id="ref-for-idl-unsigned-long-long⑦">unsigned long long</a></code>, initially 0.</p>
      <li data-md>
       <p>Let <var>observer</var> be a new <a data-link-type="dfn" href="#internal-observer" id="ref-for-internal-observer①④">internal observer</a>, initialized as follows:</p>
       <dl>
@@ -2204,7 +2209,7 @@ <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">I
   <a data-link-type="idl-name" href="https://dom.spec.whatwg.org/#abortsignal"><c- n>AbortSignal</c-></a> <a data-type="AbortSignal " href="#dom-subscribeoptions-signal"><code><c- g>signal</c-></code></a>;
 };
 
-<c- b>callback</c-> <a href="#callbackdef-predicate"><code><c- g>Predicate</c-></code></a> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any"><c- b>any</c-></a> <a href="#dom-predicate-value"><code><c- g>value</c-></code></a>);
+<c- b>callback</c-> <a href="#callbackdef-predicate"><code><c- g>Predicate</c-></code></a> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-boolean"><c- b>boolean</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any"><c- b>any</c-></a> <a href="#dom-predicate-value"><code><c- g>value</c-></code></a>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <a href="#dom-predicate-index"><code><c- g>index</c-></code></a>);
 <c- b>callback</c-> <a href="#callbackdef-reducer"><code><c- g>Reducer</c-></code></a> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any"><c- b>any</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any"><c- b>any</c-></a> <a href="#dom-reducer-accumulator"><code><c- g>accumulator</c-></code></a>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any"><c- b>any</c-></a> <a href="#dom-reducer-currentvalue"><code><c- g>currentValue</c-></code></a>);
 <c- b>callback</c-> <a href="#callbackdef-mapper"><code><c- g>Mapper</c-></code></a> = <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any"><c- b>any</c-></a> (<a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-any"><c- b>any</c-></a> <a href="#dom-mapper-element"><code><c- g>element</c-></code></a>, <a class="idl-code" data-link-type="interface" href="https://webidl.spec.whatwg.org/#idl-unsigned-long-long"><c- b>unsigned</c-> <c- b>long</c-> <c- b>long</c-></a> <a href="#dom-mapper-index"><code><c- g>index</c-></code></a>);
 // Differs from Mapper only in return type, since this callback is exclusively
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