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[JSC] Implement Iterator.prototype.reduce from Iterator Helpers Proposal
https://bugs.webkit.org/show_bug.cgi?id=279726 Reviewed by Yusuke Suzuki. Implement `Iterator.prototype.reduce`[1] from Iterator Helpers Proposal[2]. [1]: https://tc39.es/proposal-iterator-helpers/#sec-iteratorprototype.reduce [2]: https://github.com/tc39/proposal-iterator-helpers * JSTests/stress/iterator-prototype-reduce.js: Added. (assert): (sameArray): (shouldThrow): (throw.new.Error.Iter.prototype.get next): (throw.new.Error.Iter): (throw.new.Error): (sameArray.Iter.prototype.next): (sameArray.Iter): (sameValue.Iter.prototype.next): (sameValue.Iter): (sameValue): (prototype.next): (iter.reduce.Iter.prototype.get next): (iter.reduce.Iter.prototype.get return): (iter.reduce.Iter): (iter.reduce): * JSTests/test262/expectations.yaml: * Source/JavaScriptCore/builtins/JSIteratorPrototype.js: (reduce.wrapper.return.next): (reduce.wrapper.return.get return): (reduce.wrapper.iterator): (reduce): * Source/JavaScriptCore/runtime/JSIteratorPrototype.cpp: (JSC::JSIteratorPrototype::finishCreation): Canonical link: https://commits.webkit.org/283697@main
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‎JSTests/stress/iterator-prototype-reduce.js‎

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//@ requireOptions("--useIteratorHelpers=1")
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function assert(a, text) {
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if (!a)
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throw new Error(`Failed assertion: ${text}`);
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}
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function sameValue(a, b) {
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if (a !== b)
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throw new Error(`Expected ${b} but got ${a}`);
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}
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function sameArray(a, b) {
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sameValue(JSON.stringify(a), JSON.stringify(b));
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}
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function shouldThrow(fn, error, message) {
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try {
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fn();
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throw new Error('Expected to throw, but succeeded');
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} catch (e) {
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if (!(e instanceof error))
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throw new Error(`Expected to throw ${error.name} but got ${e.name}`);
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if (e.message !== message)
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throw new Error(`Expected ${error.name} with '${message}' but got '${e.message}'`);
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}
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}
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{
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let nextGetCount = 0;
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class Iter extends Iterator {
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i = 1;
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get next() {
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nextGetCount++;
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return function() {
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if (this.i > 5)
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return { value: this.i, done: true }
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return { value: this.i++, done: false }
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};
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};
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}
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const iter = new Iter();
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const counters = [];
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const sum = iter.reduce((acc, value, i) => {
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counters.push(i);
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return acc + value
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}, 0);
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sameValue(nextGetCount, 1);
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sameValue(sum, 15);
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sameArray(counters, [0, 1, 2, 3, 4]);
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}
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{
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class Iter extends Iterator {
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i = 1;
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next() {
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if (this.i > 1)
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return { value: this.i, done: true }
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return { value: this.i++, done: false }
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}
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}
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const iter = new Iter();
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let reducerCalls = 0;
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const initialValue = {};
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iter.reduce((acc, value, i) => {
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sameValue(acc, initialValue);
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reducerCalls++;
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}, initialValue);
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sameValue(reducerCalls, 1);
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}
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{
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class Iter extends Iterator {
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i = 1;
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next() {
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if (this.i > 5)
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return { value: this.i, done: true }
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return { value: this.i++, done: false }
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}
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};
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const iter = new Iter();
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const counters = [];
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const sum = iter.reduce((acc, value, i) => {
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counters.push(i);
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return acc + value
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});
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sameValue(sum, 15);
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sameArray(counters, [1, 2, 3, 4]);
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}
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{
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class Iter extends Iterator {
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next() { return { value: 1, done: true }; }
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};
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const iter = new Iter();
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shouldThrow(() => {
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iter.reduce(() => {});
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}, TypeError, "Iterator.prototype.reduce requires an initial value or an iterator that is not done.");
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}
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{
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class Iter extends Iterator {
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next() { return 3; }
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};
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const iter = new Iter();
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shouldThrow(() => {
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iter.reduce(() => {});
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}, TypeError, "Iterator result interface is not an object.");
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}
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{
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let nextGetCount = 0;
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let returnGetCount = 0;
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class Iter extends Iterator {
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get next() {
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nextGetCount++;
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return function () {
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return { value: 2, done: false }
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}
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};
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get return() {
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returnGetCount++;
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return function() {
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return {};
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};
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};
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};
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const iter = new Iter();
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shouldThrow(() => {
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iter.reduce(() => {
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sameValue(returnGetCount, 0);
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sameValue(nextGetCount, 1);
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throw new Error("my error");
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});
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}, Error, "my error");
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sameValue(nextGetCount, 1);
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sameValue(returnGetCount, 1);
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}

‎JSTests/test262/expectations.yaml‎

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@@ -457,81 +457,6 @@ test/built-ins/Iterator/prototype/map/underlying-iterator-closed-in-parallel.js:
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test/built-ins/Iterator/prototype/map/underlying-iterator-closed.js:
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default: "TypeError: iterator.map is not a function. (In 'iterator.map(() => 0)', 'iterator.map' is undefined)"
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strict mode: "TypeError: iterator.map is not a function. (In 'iterator.map(() => 0)', 'iterator.map' is undefined)"
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test/built-ins/Iterator/prototype/reduce/argument-effect-order.js:
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default: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.reduce.call')"
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strict mode: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.reduce.call')"
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test/built-ins/Iterator/prototype/reduce/callable.js:
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default: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.reduce.call')"
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strict mode: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.reduce.call')"
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test/built-ins/Iterator/prototype/reduce/get-next-method-only-once.js:
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default: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(x => x)', 'iterator.reduce' is undefined)"
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strict mode: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(x => x)', 'iterator.reduce' is undefined)"
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test/built-ins/Iterator/prototype/reduce/get-next-method-throws.js:
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default: 'Test262Error: Expected a Test262Error but got a TypeError'
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strict mode: 'Test262Error: Expected a Test262Error but got a TypeError'
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test/built-ins/Iterator/prototype/reduce/is-function.js:
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default: 'Test262Error: Expected SameValue(«undefined», «function») to be true'
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strict mode: 'Test262Error: Expected SameValue(«undefined», «function») to be true'
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test/built-ins/Iterator/prototype/reduce/iterator-already-exhausted-initial-value.js:
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default: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {}, initialValue)', 'iterator.reduce' is undefined)"
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strict mode: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {}, initialValue)', 'iterator.reduce' is undefined)"
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test/built-ins/Iterator/prototype/reduce/iterator-already-exhausted-no-initial-value.js:
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default: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {}, 0)', 'iterator.reduce' is undefined)"
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strict mode: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {}, 0)', 'iterator.reduce' is undefined)"
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test/built-ins/Iterator/prototype/reduce/iterator-yields-once-initial-value.js:
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default: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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strict mode: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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test/built-ins/Iterator/prototype/reduce/iterator-yields-once-no-initial-value.js:
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default: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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strict mode: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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test/built-ins/Iterator/prototype/reduce/length.js:
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default: "TypeError: undefined is not an object (evaluating 'Object.getOwnPropertyDescriptor(obj, name)')"
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strict mode: "TypeError: undefined is not an object (evaluating 'Object.getOwnPropertyDescriptor(obj, name)')"
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test/built-ins/Iterator/prototype/reduce/name.js:
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default: "TypeError: undefined is not an object (evaluating 'Object.getOwnPropertyDescriptor(obj, name)')"
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strict mode: "TypeError: undefined is not an object (evaluating 'Object.getOwnPropertyDescriptor(obj, name)')"
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test/built-ins/Iterator/prototype/reduce/next-method-returns-throwing-done.js:
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default: 'Test262Error: Expected a Test262Error but got a TypeError'
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strict mode: 'Test262Error: Expected a Test262Error but got a TypeError'
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test/built-ins/Iterator/prototype/reduce/next-method-returns-throwing-value-done.js:
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default: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {}, 0)', 'iterator.reduce' is undefined)"
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strict mode: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {}, 0)', 'iterator.reduce' is undefined)"
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test/built-ins/Iterator/prototype/reduce/next-method-returns-throwing-value.js:
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default: 'Test262Error: Expected a Test262Error but got a TypeError'
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strict mode: 'Test262Error: Expected a Test262Error but got a TypeError'
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test/built-ins/Iterator/prototype/reduce/next-method-throws.js:
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default: 'Test262Error: Expected a Test262Error but got a TypeError'
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strict mode: 'Test262Error: Expected a Test262Error but got a TypeError'
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test/built-ins/Iterator/prototype/reduce/non-callable-reducer.js:
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default: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {})', 'iterator.reduce' is undefined)"
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strict mode: "TypeError: iterator.reduce is not a function. (In 'iterator.reduce(() => {})', 'iterator.reduce' is undefined)"
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test/built-ins/Iterator/prototype/reduce/prop-desc.js:
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default: 'Test262Error: obj should have an own property reduce'
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strict mode: 'Test262Error: obj should have an own property reduce'
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test/built-ins/Iterator/prototype/reduce/proto.js:
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default: "TypeError: undefined is not an object (evaluating 'Object.getPrototypeOf(Iterator.prototype.reduce)')"
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strict mode: "TypeError: undefined is not an object (evaluating 'Object.getPrototypeOf(Iterator.prototype.reduce)')"
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test/built-ins/Iterator/prototype/reduce/reducer-args-initial-value.js:
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default: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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strict mode: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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test/built-ins/Iterator/prototype/reduce/reducer-args-no-initial-value.js:
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default: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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strict mode: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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test/built-ins/Iterator/prototype/reduce/reducer-memo-can-be-any-type.js:
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default: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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strict mode: "TypeError: iter.reduce is not a function. (In 'iter.reduce((memo, v, count) => {"
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test/built-ins/Iterator/prototype/reduce/reducer-this.js:
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default: "TypeError: iter.reduce is not a function. (In 'iter.reduce(function (memo, v, count) {"
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strict mode: "TypeError: iter.reduce is not a function. (In 'iter.reduce(function (memo, v, count) {"
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test/built-ins/Iterator/prototype/reduce/reducer-throws-then-closing-iterator-also-throws.js:
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default: 'Test262Error: Expected a Test262Error but got a TypeError'
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strict mode: 'Test262Error: Expected a Test262Error but got a TypeError'
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test/built-ins/Iterator/prototype/reduce/reducer-throws.js:
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default: 'Test262Error: Expected a Test262Error but got a TypeError'
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strict mode: 'Test262Error: Expected a Test262Error but got a TypeError'
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test/built-ins/Iterator/prototype/reduce/this-plain-iterator.js:
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default: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.reduce.call')"
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strict mode: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.reduce.call')"
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test/built-ins/Iterator/prototype/take/argument-effect-order.js:
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default: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.take.call')"
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strict mode: "TypeError: undefined is not an object (evaluating 'Iterator.prototype.take.call')"

‎Source/JavaScriptCore/builtins/JSIteratorPrototype.js‎

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@@ -88,3 +88,48 @@ function find(predicate)
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return @undefined;
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}
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// https://tc39.es/proposal-iterator-helpers/#sec-iteratorprototype.reduce
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function reduce(reducer /*, initialValue */)
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{
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"use strict";
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if (!@isObject(this))
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@throwTypeError("Iterator.prototype.reduce requires that |this| be an Object.");
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if (!@isCallable(reducer))
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@throwTypeError("Iterator.prototype.reduce reducer argument must be a function.");
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var initialValue = @argument(1);
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var iteratedIterator = this;
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var iteratedNextMethod = this.next;
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var accumulator;
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var counter = 0;
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if (initialValue === @undefined) {
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var result = iteratedNextMethod.@call(iteratedIterator);
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if (!@isObject(result))
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@throwTypeError("Iterator result interface is not an object.");
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if (result.done)
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@throwTypeError("Iterator.prototype.reduce requires an initial value or an iterator that is not done.");
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accumulator = result.value;
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counter = 1;
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} else
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accumulator = initialValue;
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var wrapper = {
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@@iterator: function()
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{
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return {
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next: function() { return iteratedNextMethod.@call(iteratedIterator); },
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get return() { return iteratedIterator.return; },
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};
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},
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};
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for (var item of wrapper) {
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accumulator = reducer(accumulator, item, counter++);
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}
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return accumulator;
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}

‎Source/JavaScriptCore/runtime/JSIteratorPrototype.cpp‎

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@@ -75,6 +75,8 @@ void JSIteratorPrototype::finishCreation(VM& vm, JSGlobalObject* globalObject)
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JSC_BUILTIN_FUNCTION_WITHOUT_TRANSITION(vm.propertyNames->builtinNames().everyPublicName(), jsIteratorPrototypeEveryCodeGenerator, static_cast<unsigned>(PropertyAttribute::DontEnum));
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// https://tc39.es/proposal-iterator-helpers/#sec-iteratorprototype.find
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JSC_BUILTIN_FUNCTION_WITHOUT_TRANSITION(vm.propertyNames->builtinNames().findPublicName(), jsIteratorPrototypeFindCodeGenerator, static_cast<unsigned>(PropertyAttribute::DontEnum));
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// https://tc39.es/proposal-iterator-helpers/#sec-iteratorprototype.reduce
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JSC_BUILTIN_FUNCTION_WITHOUT_TRANSITION(vm.propertyNames->builtinNames().reducePublicName(), jsIteratorPrototypeReduceCodeGenerator, static_cast<unsigned>(PropertyAttribute::DontEnum));
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}
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}
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