Issue #2246 - Implement Array find from last.

Based on the implementation from Mozilla bug 1704385.

js/src/builtin/Array.js

@@ -1210,6 +1210,72 @@ function ArrayAt(index) {
     return O[k];
 }
 
+// https://github.com/tc39/proposal-array-find-from-last
+// Array.prototype.findLast ( predicate, thisArg )
+function ArrayFindLast(predicate/*, thisArg*/) {
+    /* Steps 1. */
+    var O = ToObject(this);
+
+    /* Steps 2. */
+    var len = ToLength(O.length);
+
+    /* Step 3. */
+    if (arguments.length === 0) {
+        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, "Array.prototype.findLast");
+    }
+    if (!IsCallable(predicate)) {
+        ThrowTypeError(JSMSG_NOT_FUNCTION, DecompileArg(0, predicate));
+    }
+
+    var T = arguments.length > 1 ? arguments[1] : undefined;
+
+    /* Step 4-5. */
+    for (var k = len - 1; k >= 0; k--) {
+        /* Steps 5.a-b. */
+        var kValue = O[k];
+        /* Steps 5.c-d. */
+        if (callContentFunction(predicate, T, kValue, k, O)) {
+            return kValue;
+        }
+    }
+
+    /* Step 6. */
+    return undefined;
+}
+
+// https://github.com/tc39/proposal-array-find-from-last
+// Array.prototype.findLastIndex ( predicate, thisArg )
+function ArrayFindLastIndex(predicate/*, thisArg*/) {
+    /* Steps 1. */
+    var O = ToObject(this);
+
+    /* Steps 2. */
+    var len = ToLength(O.length);
+
+    /* Step 3. */
+    if (arguments.length === 0) {
+        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, "Array.prototype.findLastIndex");
+    }
+    if (!IsCallable(predicate)) {
+        ThrowTypeError(JSMSG_NOT_FUNCTION, DecompileArg(0, predicate));
+    }
+
+    var T = arguments.length > 1 ? arguments[1] : undefined;
+
+    /* Step 4-5. */
+    for (var k = len - 1; k >= 0; k--) {
+        /* Steps 5.a-b. */
+        var kValue = O[k];
+        /* Steps 5.c-d. */
+        if (callContentFunction(predicate, T, kValue, k, O)) {
+            return k;
+        }
+    }
+
+    /* Step 6. */
+    return -1;
+}
+
 function ArrayStaticConcat(arr, arg1) {
     if (arguments.length < 1)
         ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, 'Array.concat');

js/src/builtin/TypedArray.js

@@ -1347,6 +1347,91 @@ function TypedArrayAt(index) {
     return obj[k];
 }
 
+// https://github.com/tc39/proposal-array-find-from-last
+// %TypedArray%.prototype.findLast ( predicate, thisArg )
+function TypedArrayFindLast(predicate/*, thisArg*/) {
+    // Step 1.
+    var O = this;
+
+    // Step 2.
+    var isTypedArray = IsTypedArrayEnsuringArrayBuffer(O);
+
+    // If we got here, `this` is either a typed array or a wrapper for one.
+
+    // Step 3.
+    var len;
+    if (isTypedArray) {
+        len = TypedArrayLength(O);
+    } else {
+        len = callFunction(CallTypedArrayMethodIfWrapped, O, "TypedArrayLengthMethod");
+    }
+
+    // Step 4.
+    if (arguments.length === 0) {
+        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, "%TypedArray%.prototype.findLast");
+    }
+    if (!IsCallable(predicate)) {
+        ThrowTypeError(JSMSG_NOT_FUNCTION, DecompileArg(0, predicate));
+    }
+
+    var thisArg = arguments.length > 1 ? arguments[1] : void 0;
+
+    // Steps 5-6.
+    for (var k = len - 1; k >= 0; k--) {
+        // Steps 6.a-b.
+        var kValue = O[k];
+
+        // Steps 6.c-d.
+        if (callContentFunction(predicate, thisArg, kValue, k, O)) {
+            return kValue;
+        }
+    }
+
+    // Step 7.
+    return undefined;
+}
+
+// https://github.com/tc39/proposal-array-find-from-last
+// %TypedArray%.prototype.findLastIndex ( predicate, thisArg )
+function TypedArrayFindLastIndex(predicate/*, thisArg*/) {
+    // Step 1.
+    var O = this;
+
+    // Step 2.
+    var isTypedArray = IsTypedArrayEnsuringArrayBuffer(O);
+
+    // If we got here, `this` is either a typed array or a wrapper for one.
+
+    // Step 3.
+    var len;
+    if (isTypedArray) {
+        len = TypedArrayLength(O);
+    } else {
+        len = callFunction(CallTypedArrayMethodIfWrapped, O, "TypedArrayLengthMethod");
+    }
+
+    // Step 4.
+    if (arguments.length === 0) {
+        ThrowTypeError(JSMSG_MISSING_FUN_ARG, 0, "%TypedArray%.prototype.findLastIndex");
+    }
+    if (!IsCallable(predicate)) {
+        ThrowTypeError(JSMSG_NOT_FUNCTION, DecompileArg(0, predicate));
+    }
+
+    var thisArg = arguments.length > 1 ? arguments[1] : void 0;
+
+    // Steps 5-6.
+    for (var k = len - 1; k >= 0; k--) {
+        // Steps 6.a-f.
+        if (callContentFunction(predicate, thisArg, O[k], k, O)) {
+            return k;
+        }
+    }
+
+    // Step 7.
+    return -1;
+}
+
 // ES6 draft rev30 (2014/12/24) 22.2.3.30 %TypedArray%.prototype.values()
 function TypedArrayValues() {
     // Step 1.

js/src/jsarray.cpp

@@ -3191,6 +3191,10 @@ static const JSFunctionSpec array_methods[] = {
     
     /* ES2022 additions */
     JS_SELF_HOSTED_FN("at",          "ArrayAt",          1,0),
+
+    /* ES2023 proposals */
+    JS_SELF_HOSTED_FN("findLast",    "ArrayFindLast",    1,0),
+    JS_SELF_HOSTED_FN("findLastIndex", "ArrayFindLastIndex", 1,0),
     
     JS_FS_END
 };
@@ -3356,6 +3360,8 @@ array_proto_finish(JSContext* cx, JS::HandleObject ctor, JS::HandleObject proto)
         !DefineProperty(cx, unscopables, cx->names().fill, value) ||
         !DefineProperty(cx, unscopables, cx->names().find, value) ||
         !DefineProperty(cx, unscopables, cx->names().findIndex, value) ||
+        !DefineProperty(cx, unscopables, cx->names().findLast, value) ||
+        !DefineProperty(cx, unscopables, cx->names().findLastIndex, value) ||
         !DefineProperty(cx, unscopables, cx->names().flat, value) ||
         !DefineProperty(cx, unscopables, cx->names().flatMap, value) ||
         !DefineProperty(cx, unscopables, cx->names().includes, value) ||

js/src/vm/CommonPropertyNames.h

@@ -135,6 +135,8 @@
     macro(finally, finally_, "finally") \
     macro(find, find, "find") \
     macro(findIndex, findIndex, "findIndex") \
+    macro(findLast, findLast, "findLast") \
+    macro(findLastIndex, findLastIndex, "findLastIndex") \
     macro(firstDayOfWeek, firstDayOfWeek, "firstDayOfWeek") \
     macro(fix, fix, "fix") \
     macro(flags, flags, "flags") \

js/src/vm/TypedArrayObject.cpp

@@ -1486,6 +1486,8 @@ TypedArrayObject::protoFunctions[] = {
     JS_SELF_HOSTED_FN("filter", "TypedArrayFilter", 1, 0),
     JS_SELF_HOSTED_FN("find", "TypedArrayFind", 1, 0),
     JS_SELF_HOSTED_FN("findIndex", "TypedArrayFindIndex", 1, 0),
+    JS_SELF_HOSTED_FN("findLast", "TypedArrayFindLast", 1, 0),
+    JS_SELF_HOSTED_FN("findLastIndex", "TypedArrayFindLastIndex", 1, 0),
     JS_SELF_HOSTED_FN("forEach", "TypedArrayForEach", 1, 0),
     JS_SELF_HOSTED_FN("indexOf", "TypedArrayIndexOf", 2, 0),
     JS_SELF_HOSTED_FN("join", "TypedArrayJoin", 1, 0),