From 76f7ae64cfb657de66f6f12f04d2f6a03b99c3e2 Mon Sep 17 00:00:00 2001
From: Rolf Martin Glomsrud <rolf.martin@glomsrud.no>
Date: Mon, 10 Jan 2022 15:24:49 +0000
Subject: [PATCH] Bug 1739648 - implement groupBy r=arai

Depends on D133870

Differential Revision: https://phabricator.services.mozilla.com/D133881
---
 js/src/builtin/Array.cpp                      |  1 +
 js/src/builtin/Array.js                       | 82 +++++++++++++++++--
 js/xpconnect/tests/chrome/test_xrayToJS.xhtml |  2 +-
 3 files changed, 75 insertions(+), 10 deletions(-)

diff --git a/js/src/builtin/Array.cpp b/js/src/builtin/Array.cpp
index 7a9ecb6797cd..710f7da03c7b 100644
--- a/js/src/builtin/Array.cpp
+++ b/js/src/builtin/Array.cpp
@@ -3839,6 +3839,7 @@ static const JSFunctionSpec array_methods[] = {
     JS_SELF_HOSTED_FN("forEach", "ArrayForEach", 1, 0),
     JS_SELF_HOSTED_FN("map", "ArrayMap", 1, 0),
     JS_SELF_HOSTED_FN("filter", "ArrayFilter", 1, 0),
+    JS_SELF_HOSTED_FN("groupBy", "ArrayGroupBy", 1, 0),
     JS_SELF_HOSTED_FN("groupByToMap", "ArrayGroupByToMap", 1, 0),
     JS_SELF_HOSTED_FN("reduce", "ArrayReduce", 1, 0),
     JS_SELF_HOSTED_FN("reduceRight", "ArrayReduceRight", 1, 0),
diff --git a/js/src/builtin/Array.js b/js/src/builtin/Array.js
index 7d2b7f4f61d8..f34ca7b89795 100644
--- a/js/src/builtin/Array.js
+++ b/js/src/builtin/Array.js
@@ -307,6 +307,70 @@ function ArrayFilter(callbackfn/*, thisArg*/) {
     return A;
 }
 
+// Array Grouping proposal
+//
+// Array.prototype.groupBy
+// https://tc39.es/proposal-array-grouping/#sec-array.prototype.groupby
+function ArrayGroupBy(callbackfn/*, thisArg*/) {
+    /* Step 1. Let O be ? ToObject(this value). */
+    var O = ToObject(this);
+
+    /* Step 2. Let len be ? LengthOfArrayLike(O). */
+    var len = ToLength(O.length);
+
+    /* Step 3. If IsCallable(callbackfn) is false, throw a TypeError exception. */
+    if (!IsCallable(callbackfn)) {
+        ThrowTypeError(JSMSG_NOT_FUNCTION, DecompileArg(0, callbackfn));
+    }
+
+    /* Step 5. Let groups be a new empty List. */
+    var groups = new_List();
+
+    var T = arguments.length > 1 ? arguments[1] : void 0;
+
+    /* Steps 4, 6. */
+    for (var k = 0; k < len; k++) {
+
+        /* Skip Step 6.a. Let Pk be ! ToString(𝔽(k)).
+         *
+         * k is coerced into a string through the property access. */
+
+        /* Step 6.b. Let kValue be ? Get(O, Pk). */
+        var kValue = O[k];
+
+        /* Step 6.c.
+         * Let propertyKey be ? ToPropertyKey(
+         *   ? Call(callbackfn, thisArg, « kValue, 𝔽(k), O »)).
+         */
+        var propertyKey = TO_PROPERTY_KEY(
+          callContentFunction(callbackfn, T, kValue, k, O)
+        );
+
+        /* Step 6.d. Perform ! AddValueToKeyedGroup(groups, propertyKey, kValue). */
+        if (!groups[propertyKey]) {
+            var elements = [ kValue ];
+            DefineDataProperty(groups, propertyKey, elements);
+        } else {
+            var lenElements = groups[propertyKey].length;
+            DefineDataProperty(groups[propertyKey], lenElements, kValue);
+        }
+    }
+
+    /* Step 7. Let obj be ! OrdinaryObjectCreate(null). */
+    var object = {};
+
+    /* Step 8. For each Record { [[Key]], [[Elements]] } g of groups, do
+     *  a. Let elements be ! CreateArrayFromList(g.[[Elements]]).
+     *  b. Perform ! CreateDataPropertyOrThrow(obj, g.[[Key]], elements).
+     */
+    for (var propertyKey in groups) {
+        DefineDataProperty(object, propertyKey, groups[propertyKey])
+    }
+
+    /* Step 9. Return obj. */
+    return object;
+}
+
 // Array Grouping proposal
 //
 // Array.prototype.groupByToMap
@@ -338,39 +402,39 @@ function ArrayGroupByToMap(callbackfn/*, thisArg*/) {
 
     var T = arguments.length > 1 ? arguments[1] : void 0;
 
-    /* Combined Step 6. and Step 8.
+    /* Combine Step 6. and Step 8.
      *
      * We have direct access to the map constructor and set/get methods.
      * We can treat these two loops as one, as there isn't a risk that user
      * polyfilling will impact the implementation.
      */
-    for(var k = 0; k<len; k++){
-        /* Skipping Step 6.a Let Pk be ! ToString(𝔽(k)).
+    for (var k = 0; k < len; k++) {
+        /* Skipping Step 6.a. Let Pk be ! ToString(𝔽(k)).
          *
          * Value is coerced to String by property access in step 6.b.
          */
 
-        /* Step 6.b Let kValue be ? Get(O, Pk). */
+        /* Step 6.b. Let kValue be ? Get(O, Pk). */
         var kValue = O[k];
 
-        /* Step 6.c
+        /* Step 6.c.
          * Let key be ? Call(callbackfn, thisArg, « kValue, 𝔽(k), O »).
          */
         var propertyKey = callContentFunction(callbackfn,T, kValue, k, O);
 
-        /* Skipping Step 6.d If key is -0𝔽, set key to +0𝔽.
+        /* Skipping Step 6.d. If key is -0𝔽, set key to +0𝔽.
          *
          * This step is performed by std_Map_set.
          */
 
-        /* Step 8.c Append entry as the last element of map.[[MapData]].
+        /* Step 8.c. Append entry as the last element of map.[[MapData]].
          *
          * We are not using an intermediate object to store the values.
          * So, this step applies it directly to the map object. Skips steps
          * 6.e (Perform ! AddValueToKeyedGroup(groups, key, kValue))
          * and 8.a-b as a result.
          */
-        if(!callFunction(std_Map_get, map, propertyKey)){
+        if (!callFunction(std_Map_get, map, propertyKey)) {
             var elements = [ kValue ];
             callFunction(std_Map_set, map, propertyKey, elements);
         } else {
@@ -1313,7 +1377,7 @@ function ArrayWithSorted(comparefn) {
     var items = std_Array(len);
 
     /* Steps 5-6. */
-    for(var k = 0; k < len; k++) {
+    for (var k = 0; k < len; k++) {
         DefineDataProperty(items, k, O[k]);
     }
 
diff --git a/js/xpconnect/tests/chrome/test_xrayToJS.xhtml b/js/xpconnect/tests/chrome/test_xrayToJS.xhtml
index 71755550fe8e..225c8d17d00c 100644
--- a/js/xpconnect/tests/chrome/test_xrayToJS.xhtml
+++ b/js/xpconnect/tests/chrome/test_xrayToJS.xhtml
@@ -231,7 +231,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=933681
       "pop", "shift", "unshift", "splice", "concat", "slice", "lastIndexOf", "indexOf",
       "includes", "forEach", "map", "reduce", "reduceRight", "filter", "some", "every", "find",
       "findIndex", "copyWithin", "fill", Symbol.iterator, Symbol.unscopables, "entries", "keys",
-      "values", "constructor", "flat", "flatMap", "at", "groupByToMap"];
+      "values", "constructor", "flat", "flatMap", "at", "groupBy", "groupByToMap"];
   gConstructorProperties['Array'] =
     constructorProps(["isArray", "from", "of", Symbol.species]);
   for (var c of typedArrayClasses) {