Iterator Helpers (#2818)

drop:

property descriptor
name
length
[[Prototype]]
is a function
is not constructible
result instanceof Iterator
limit is given a non-primitive that needs to be converted to a number
  through valueOf
  through toString (array)
limit coercion to number throws
limit converts to NaN
  same as limit not supplied
limit behaves properly
  limit < number of values
  limit = number of values
  limit > number of values
gets the next method from the underlying iterator only once
underlying iterator has throwing next getter
underlying iterator next throws when advancing past dropped items
underlying iterator is advanced after calling drop
underlying iterator is closed after calling drop
underlying iterator is already closed
underlying iterator next returns non-object
underlying iterator next returns object with throwing done/value getters
underlying iterator return is never called when result iterator is closed

every:

property descriptor
name
length
[[Prototype]]
is a function
is callable
is not constructible
result is a Boolean
predicate is non-callable
iterator already exhausted
called on non-object
called on object with "next" method
called on object with non-callable "next" method
predicate returns non-Boolean
predicate returns truthy for all iterated values
  returns true
predicate returns truthy for some iterated values but then falsey for at least one iterated value
  returns false
  iteration stops
  iterator is closed
predicate returns falsey immediately
  returns false
  iteration stops
  iterator is closed
predicate throws
  every throws
  iterator is closed
predicate throws then iterator close also throws
predicate this value is undefined
predicate is passed the yielded value as the first parameter and a counter as second parameter
gets the next method from the iterator only once
iterator has throwing next getter
iterator has throwing return getter
iterator next throws
iterator return throws
iterator next returns non-object
iterator next returns object with throwing done/value getters

Co-authored-by: Michael Ficarra <mficarra@shapesecurity.com>
Co-authored-by: Jordan Harband <ljharb@gmail.com>

features.txt

@@ -104,6 +104,10 @@ String.prototype.toWellFormed
 # https://github.com/tc39/proposal-json-parse-with-source
 json-parse-with-source
 
+# Iterator Helpers
+# https://github.com/tc39/proposal-iterator-helpers
+iterator-helpers
+
 ## Standard language features
 #
 # Language features that have been included in a published version of the

test/built-ins/Iterator/constructor.js

@@ -0,0 +1,11 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iterator-constructor
+description: >
+  The Iterator constructor is a built-in function
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(typeof Iterator, 'function', 'The value of `typeof Iterator` is "function"');

test/built-ins/Iterator/from/callable.js

@@ -0,0 +1,12 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from is callable
+features: [iterator-helpers]
+---*/
+function* g() {}
+
+Iterator.from(g());
+Iterator.from.call(null, g());

test/built-ins/Iterator/from/get-next-method-only-once.js

@@ -0,0 +1,46 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Gets the next method from the underlying iterator only once
+info: |
+  Iterator.from ( O )
+
+  2. Let iteratorRecord be ? GetIteratorFlattenable(O).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let nextGets = 0;
+let nextCalls = 0;
+
+class CountingIterator {
+  get next() {
+    ++nextGets;
+    let iter = (function* () {
+      for (let i = 1; i < 5; ++i) {
+        yield i;
+      }
+    })();
+    return function () {
+      ++nextCalls;
+      return iter.next();
+    };
+  }
+}
+
+let iterator = new CountingIterator();
+
+assert.sameValue(nextGets, 0, 'The value of `nextGets` is 0');
+assert.sameValue(nextCalls, 0, 'The value of `nextCalls` is 0');
+
+iterator = Iterator.from(iterator);
+
+assert.sameValue(nextGets, 1, 'The value of `nextGets` is 1');
+assert.sameValue(nextCalls, 0, 'The value of `nextCalls` is 0');
+
+iterator.toArray();
+
+assert.sameValue(nextGets, 1, 'The value of `nextGets` is 1');
+assert.sameValue(nextCalls, 5, 'The value of `nextCalls` is 5');

test/built-ins/Iterator/from/get-next-method-throws.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Underlying iterator has throwing next getter
+info: |
+  Iterator.from ( O )
+
+  4. Let iterated be ? GetIteratorDirect(O).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator {
+  get next() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new ThrowingIterator();
+
+assert.throws(Test262Error, function () {
+  Iterator.from(iterator);
+});

test/built-ins/Iterator/from/is-function.js

@@ -0,0 +1,10 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from is a built-in function
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(typeof Iterator.from, 'function', 'The value of `typeof Iterator.from` is "function"');

test/built-ins/Iterator/from/iterable-primitives.js

@@ -0,0 +1,39 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from does not respect the iterability of any primitive except Strings
+info: |
+  Iterator.from ( O )
+
+  1. If O is a String, set O to ! ToObject(O).
+  2. Let iteratorRecord be ? GetIteratorFlattenable(O).
+
+includes: [compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+}
+
+Number.prototype[Symbol.iterator] = function* () {
+  let i = 0;
+  let target = this >>> 0;
+  while (i < target) {
+    yield i;
+    ++i;
+  }
+};
+
+assert.compareArray(Array.from(5), [0, 1, 2, 3, 4]);
+
+assert.throws(TypeError, function () {
+  Iterator.from(5);
+});
+
+assert.compareArray(Array.from(Iterator.from(new Number(5))), [0, 1, 2, 3, 4]);
+
+assert.compareArray(Array.from(Iterator.from('string')), ['s', 't', 'r', 'i', 'n', 'g']);

test/built-ins/Iterator/from/iterable-to-iterator-fallback.js

@@ -0,0 +1,51 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from falls back to treating its parameter as an iterator if the Symbol.iterator property is null/undefined
+info: |
+  Iterator.from ( O )
+
+includes: [compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+  yield 1;
+  yield 2;
+}
+
+let iter = (function () {
+  let n = g();
+  return {
+    [Symbol.iterator]: 0,
+    next: () => n.next(),
+  };
+})();
+
+assert.throws(TypeError, function () {
+  Iterator.from(iter);
+});
+
+iter = (function () {
+  let n = g();
+  return {
+    [Symbol.iterator]: null,
+    next: () => n.next(),
+  };
+})();
+
+assert.compareArray(Array.from(Iterator.from(iter)), [0, 1, 2]);
+
+iter = (function () {
+  let n = g();
+  return {
+    [Symbol.iterator]: undefined,
+    next: () => n.next(),
+  };
+})();
+
+assert.compareArray(Array.from(Iterator.from(iter)), [0, 1, 2]);

test/built-ins/Iterator/from/length.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from has a "length" property whose value is 1.
+info: |
+  ECMAScript Standard Built-in Objects
+
+  Unless otherwise specified, the length property of a built-in
+  Function object has the attributes { [[Writable]]: false, [[Enumerable]]:
+  false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.from, 'length', {
+  value: 1,
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/from/name.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  The "name" property of Iterator.from
+info: |
+  17 ECMAScript Standard Built-in Objects
+
+  Every built-in Function object, including constructors, that is not
+  identified as an anonymous function has a name property whose value is a
+  String. Unless otherwise specified, this value is the name that is given to
+  the function in this specification.
+
+  ...
+
+  Unless otherwise specified, the name property of a built-in Function
+  object, if it exists, has the attributes { [[Writable]]: false,
+  [[Enumerable]]: false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.from, 'name', {
+  value: 'from',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/from/non-constructible.js

@@ -0,0 +1,23 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from is not constructible.
+
+  Built-in function objects that are not identified as constructors do not implement the [[Construct]] internal method unless otherwise specified in the description of a particular function.
+features: [iterator-helpers]
+---*/
+function* g() {}
+
+assert.throws(TypeError, () => {
+  new Iterator.from();
+});
+
+assert.throws(TypeError, () => {
+  new Iterator.from(g());
+});
+
+assert.throws(TypeError, () => {
+  new class extends Iterator {}.from(g());
+});

test/built-ins/Iterator/from/primitives.js

@@ -0,0 +1,38 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from throws on primitives (except Strings)
+info: |
+  Iterator.from ( O )
+
+features: [iterator-helpers]
+flags: []
+---*/
+
+assert.throws(TypeError, function () {
+  Iterator.from(null);
+});
+
+assert.throws(TypeError, function () {
+  Iterator.from(undefined);
+});
+
+assert.throws(TypeError, function () {
+  Iterator.from(0);
+});
+
+assert.throws(TypeError, function () {
+  Iterator.from(0n);
+});
+
+assert.throws(TypeError, function () {
+  Iterator.from(true);
+});
+
+assert.throws(TypeError, function () {
+  Iterator.from(Symbol());
+});
+
+Iterator.from('string');

test/built-ins/Iterator/from/prop-desc.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Property descriptor of Iterator.from
+info: |
+  Iterator.from
+
+  * is the initial value of the Iterator.from property of the global object.
+
+  17 ECMAScript Standard Built-in Objects
+
+  Every other data property described in clauses 18 through 26 and in Annex B.2
+  has the attributes { [[Writable]]: true, [[Enumerable]]: false,
+  [[Configurable]]: true } unless otherwise specified.
+features: [globalThis, iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator, 'from', {
+  value: Iterator.from,
+  writable: true,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/from/proto.js

@@ -0,0 +1,15 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  The value of the [[Prototype]] internal slot of Iterator.from is the
+  intrinsic object %FunctionPrototype%.
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(
+  Object.getPrototypeOf(Iterator.from),
+  Function.prototype,
+  'Object.getPrototypeOf(Iterator.from) must return the value of Function.prototype'
+);

test/built-ins/Iterator/from/result-proto.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  The value of the [[Prototype]] internal slot of the return value of Iterator.from is the
+  intrinsic object %WrapForValidIteratorPrototype%, whose [[Prototype]] is %IteratorHelperPrototype%.
+features: [iterator-helpers]
+---*/
+let iter = {
+  next() {
+    return {
+      done: true,
+      value: undefined,
+    };
+  },
+};
+
+const WrapForValidIteratorPrototype = Object.getPrototypeOf(Iterator.from(iter));
+
+assert.sameValue(Object.getPrototypeOf(WrapForValidIteratorPrototype), Iterator.prototype);
+
+class SubIterator extends Iterator {}
+assert.sameValue(Object.getPrototypeOf(SubIterator.from(iter)), WrapForValidIteratorPrototype);
+
+function* g() {}
+const GeneratorPrototype = Object.getPrototypeOf(g());
+
+assert.sameValue(Object.getPrototypeOf(Iterator.from(g())), GeneratorPrototype);

test/built-ins/Iterator/from/supports-iterable.js

@@ -0,0 +1,14 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from supports iterables
+info: |
+  Iterator.from ( O )
+
+includes: [compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+assert.compareArray(Array.from(Iterator.from([0, 1, 2, 3])), [0, 1, 2, 3]);

test/built-ins/Iterator/from/supports-iterator.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iterator.from
+description: >
+  Iterator.from supports non-iterable iterators
+info: |
+  Iterator.from ( O )
+
+includes: [compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+
+function* g() {
+  yield 0;
+  yield 1;
+  yield 2;
+  yield 3;
+}
+
+let n = g();
+let iter = {
+  next() {
+    return n.next();
+  },
+};
+
+assert.compareArray(Array.from(Iterator.from(iter)), [0, 1, 2, 3]);

test/built-ins/Iterator/length.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iterator-constructor
+description: >
+  Iterator has a "length" property whose value is 0.
+info: |
+  The Iterator Constructor
+
+  The length property of the Iterator constructor function is 0.
+  ...
+
+  ES7 section 17: Unless otherwise specified, the length property of a built-in
+  Function object has the attributes { [[Writable]]: false, [[Enumerable]]:
+  false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator, 'length', {
+  value: 0,
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/name.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iterator-constructor
+description: >
+  The "name" property of Iterator
+info: |
+  17 ECMAScript Standard Built-in Objects
+
+  Every built-in Function object, including constructors, that is not
+  identified as an anonymous function has a name property whose value is a
+  String. Unless otherwise specified, this value is the name that is given to
+  the function in this specification.
+
+  ...
+
+  Unless otherwise specified, the name property of a built-in Function
+  object, if it exists, has the attributes { [[Writable]]: false,
+  [[Enumerable]]: false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator, 'name', {
+  value: 'Iterator',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/newtarget-or-active-function-object.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iterator
+description: >
+  Iterator is not callable or constructable
+info: |
+  When the Iterator function is called, the following steps are taken:
+
+  If NewTarget is undefined or the active function object, throw a TypeError exception.
+
+features: [iterator-helpers]
+---*/
+
+assert.throws(TypeError, () => {
+  Iterator();
+});
+
+assert.throws(TypeError, () => {
+  new Iterator();
+});

test/built-ins/Iterator/prop-desc.js

@@ -0,0 +1,27 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iterator-constructor
+description: >
+  Property descriptor of Iterator
+info: |
+  The Iterator Constructor
+
+  * is the initial value of the Iterator property of the global object.
+
+  17 ECMAScript Standard Built-in Objects
+
+  Every other data property described in clauses 18 through 26 and in Annex B.2
+  has the attributes { [[Writable]]: true, [[Enumerable]]: false,
+  [[Configurable]]: true } unless otherwise specified.
+features: [globalThis, iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(globalThis, 'Iterator', {
+  value: Iterator,
+  writable: true,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/proto-from-ctor-realm.js

@@ -0,0 +1,36 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-iterator
+description: Default [[Prototype]] value derived from realm of the NewTarget.
+features: [cross-realm, iterator-helpers, Reflect, Symbol]
+---*/
+
+let other = $262.createRealm().global;
+let newTarget = new other.Function();
+let ai;
+
+newTarget.prototype = undefined;
+ai = Reflect.construct(Iterator, [1], newTarget);
+assert.sameValue(Object.getPrototypeOf(ai), other.Iterator.prototype);
+
+newTarget.prototype = null;
+ai = Reflect.construct(Iterator, [1], newTarget);
+assert.sameValue(Object.getPrototypeOf(ai), other.Iterator.prototype);
+
+newTarget.prototype = true;
+ai = Reflect.construct(Iterator, [1], newTarget);
+assert.sameValue(Object.getPrototypeOf(ai), other.Iterator.prototype);
+
+newTarget.prototype = '';
+ai = Reflect.construct(Iterator, [1], newTarget);
+assert.sameValue(Object.getPrototypeOf(ai), other.Iterator.prototype);
+
+newTarget.prototype = Symbol();
+ai = Reflect.construct(Iterator, [1], newTarget);
+assert.sameValue(Object.getPrototypeOf(ai), other.Iterator.prototype);
+
+newTarget.prototype = 0;
+ai = Reflect.construct(Iterator, [1], newTarget);
+assert.sameValue(Object.getPrototypeOf(ai), other.Iterator.prototype);

test/built-ins/Iterator/proto.js

@@ -0,0 +1,16 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-properties-of-the-iterator-constructor
+description: >
+  The value of the [[Prototype]] internal slot of the Iterator constructor is the
+  intrinsic object %FunctionPrototype%.
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(
+  Object.getPrototypeOf(Iterator),
+  Function.prototype,
+  'Object.getPrototypeOf(Iterator) must return the value of Function.prototype'
+);

test/built-ins/Iterator/prototype/Symbol.iterator/is-function.js

@@ -0,0 +1,13 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.some
+description: >
+  Iterator.prototype.some is a built-in function
+features: [Symbol.iterator]
+---*/
+const IteratorPrototype = Object.getPrototypeOf(
+  Object.getPrototypeOf([][Symbol.iterator]())
+);
+
+assert.sameValue(typeof IteratorPrototype[Symbol.iterator], 'function');

test/built-ins/Iterator/prototype/Symbol.iterator/length.js

@@ -2,7 +2,7 @@
 // This code is governed by the BSD license found in the LICENSE file.
 /*---
 es6id: 25.1.2.1
-description: Length of IteratorPrototype[ @@iterator ]
+description: Length of %IteratorPrototype%[ @@iterator ]
 info: |
     ES6 Section 17:
     Every built-in Function object, including constructors, has a length
@@ -18,13 +18,13 @@ info: |
 features: [Symbol.iterator]
 includes: [propertyHelper.js]
 ---*/
-
-var IteratorPrototype = Object.getPrototypeOf(
+const IteratorPrototype = Object.getPrototypeOf(
   Object.getPrototypeOf([][Symbol.iterator]())
 );
 
-assert.sameValue(IteratorPrototype[Symbol.iterator].length, 0);
-
-verifyNotEnumerable(IteratorPrototype[Symbol.iterator], 'length');
-verifyNotWritable(IteratorPrototype[Symbol.iterator], 'length');
-verifyConfigurable(IteratorPrototype[Symbol.iterator], 'length');
+verifyProperty(IteratorPrototype[Symbol.iterator], 'length', {
+  value: 0,
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/Symbol.iterator/name.js

@@ -21,13 +21,13 @@ info: |
 features: [Symbol.iterator]
 includes: [propertyHelper.js]
 ---*/
-
-var IteratorPrototype = Object.getPrototypeOf(
+const IteratorPrototype = Object.getPrototypeOf(
   Object.getPrototypeOf([][Symbol.iterator]())
 );
 
-assert.sameValue(IteratorPrototype[Symbol.iterator].name, '[Symbol.iterator]');
-
-verifyNotEnumerable(IteratorPrototype[Symbol.iterator], 'name');
-verifyNotWritable(IteratorPrototype[Symbol.iterator], 'name');
-verifyConfigurable(IteratorPrototype[Symbol.iterator], 'name');
+verifyProperty(IteratorPrototype[Symbol.iterator], 'name', {
+  value: '[Symbol.iterator]',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/Symbol.iterator/prop-desc.js

@@ -12,12 +12,12 @@ info: |
 features: [Symbol.iterator]
 includes: [propertyHelper.js]
 ---*/
-
-var IteratorPrototype = Object.getPrototypeOf(
+const IteratorPrototype = Object.getPrototypeOf(
   Object.getPrototypeOf([][Symbol.iterator]())
 );
 
-assert.sameValue(typeof IteratorPrototype[Symbol.iterator], 'function');
-verifyNotEnumerable(IteratorPrototype, Symbol.iterator);
-verifyWritable(IteratorPrototype, Symbol.iterator);
-verifyConfigurable(IteratorPrototype, Symbol.iterator);
+verifyProperty(IteratorPrototype, Symbol.iterator, {
+  writable: true,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/Symbol.iterator/return-val.js

@@ -2,31 +2,20 @@
 // This code is governed by the BSD license found in the LICENSE file.
 /*---
 esid: sec-%iteratorprototype%-@@iterator
-description: Return value of @@iterator on IteratorPrototype
+description: Return value of @@iterator on %IteratorPrototype%
 info: |
   %IteratorPrototype% [ @@iterator ] ( )
     1. Return the this value.
 features: [Symbol.iterator]
 ---*/
-
 const IteratorPrototype = Object.getPrototypeOf(
   Object.getPrototypeOf([][Symbol.iterator]())
 );
+
 const getIterator = IteratorPrototype[Symbol.iterator];
 
-const thisValues = [
-    {},
-    Symbol(),
-    4,
-    4n,
-    true,
-    undefined,
-    null,
-];
+const thisValues = [{}, Symbol(), 4, 4n, true, undefined, null];
 
 for (const thisValue of thisValues) {
-    assert.sameValue(
-        getIterator.call(thisValue),
-        thisValue
-    );
+  assert.sameValue(getIterator.call(thisValue), thisValue);
 }

test/built-ins/Iterator/prototype/Symbol.toStringTag/prop-desc.js

@@ -0,0 +1,20 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 25.1.2.1
+description: Property descriptor
+info: |
+    ES6 Section 17
+
+    Every other data property described in clauses 18 through 26 and in Annex
+    B.2 has the attributes { [[Writable]]: true, [[Enumerable]]: false,
+    [[Configurable]]: true } unless otherwise specified.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+verifyProperty(Iterator.prototype, Symbol.toStringTag, {
+  value: 'Iterator',
+  writable: true,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/drop/argument-effect-order.js

@@ -0,0 +1,64 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Arguments and this value are evaluated in the correct order
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+includes: [compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+let effects = [];
+
+Iterator.prototype.drop.call(
+  {
+    get next() {
+      effects.push('get next');
+      return function () {
+        return { done: true, value: undefined };
+      };
+    },
+  },
+  {
+    valueOf() {
+      effects.push('ToNumber limit');
+      return 0;
+    },
+  }
+);
+
+assert.compareArray(effects, ['ToNumber limit', 'get next']);
+
+effects = [];
+
+assert.throws(TypeError, function () {
+  Iterator.prototype.drop.call(null, {
+    valueOf() {
+      effects.push('ToNumber limit');
+      return 0;
+    },
+  });
+});
+
+assert.compareArray(effects, []);
+
+effects = [];
+
+assert.throws(RangeError, function () {
+  Iterator.prototype.drop.call(
+    {
+      get next() {
+        effects.push('get next');
+        return function () {
+          return { done: true, value: undefined };
+        };
+      },
+    },
+    NaN
+  );
+});
+
+assert.compareArray(effects, []);

test/built-ins/Iterator/prototype/drop/callable.js

@@ -0,0 +1,13 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Iterator.prototype.drop is callable
+features: [iterator-helpers]
+---*/
+function* g() {}
+Iterator.prototype.drop.call(g(), 0);
+
+let iter = g();
+iter.drop(0);

test/built-ins/Iterator/prototype/drop/exhaustion-does-not-call-return.js

@@ -0,0 +1,60 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator return is not called when result iterator is exhausted
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+    6.b.ii. Let next be ? IteratorStep(iterated).
+    6.b.iii. If next is false, return undefined.
+  6.c. Repeat,
+    6.c.i. Let next be ? IteratorStep(iterated).
+    6.c.ii. If next is false, return undefined.
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 0;
+  yield 1;
+  yield 2;
+}
+
+class TestIterator extends Iterator {
+  get next() {
+    let n = g();
+    return function() {
+      return n.next();
+    };
+  }
+  return() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new TestIterator();
+iterator = iterator.drop(0);
+iterator.next();
+iterator.next();
+iterator.next();
+iterator.next();
+iterator.next();
+
+iterator = new TestIterator();
+iterator = iterator.drop(1);
+iterator.next();
+iterator.next();
+iterator.next();
+iterator.next();
+
+iterator = new TestIterator();
+iterator = iterator.drop(1).drop(1).drop(1).drop(1).drop(1);
+iterator.next();
+iterator.next();
+
+iterator = new TestIterator();
+iterator = iterator.drop(10);
+iterator.next();
+iterator.next();

test/built-ins/Iterator/prototype/drop/get-next-method-only-once.js

@@ -0,0 +1,41 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Gets the next method from the underlying iterator only once
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let nextGets = 0;
+let nextCalls = 0;
+
+class CountingIterator extends Iterator {
+  get next() {
+    ++nextGets;
+    let iter = (function* () {
+      for (let i = 1; i < 5; ++i) {
+        yield i;
+      }
+    })();
+    return function () {
+      ++nextCalls;
+      return iter.next();
+    };
+  }
+}
+
+let iterator = new CountingIterator();
+
+assert.sameValue(nextGets, 0);
+assert.sameValue(nextCalls, 0);
+
+for (const value of iterator.drop(2));
+
+assert.sameValue(nextGets, 1);
+assert.sameValue(nextCalls, 5);

test/built-ins/Iterator/prototype/drop/get-next-method-throws.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator has throwing next getter
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  get next() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new ThrowingIterator();
+
+assert.throws(Test262Error, function () {
+  iterator.drop(0);
+});

test/built-ins/Iterator/prototype/drop/get-return-method-throws.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator return is throwing getter
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+class TestIterator extends Iterator {
+  next() {
+    return {
+      done: false,
+      value: 1,
+    };
+  }
+  get return() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new TestIterator().drop(1);
+iterator.next();
+
+assert.throws(Test262Error, function () {
+  iterator.return();
+});

test/built-ins/Iterator/prototype/drop/is-function.js

@@ -0,0 +1,10 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Iterator.prototype.drop is a built-in function
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(typeof Iterator.prototype.drop, 'function');

test/built-ins/Iterator/prototype/drop/length.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Iterator.prototype.drop has a "length" property whose value is 1.
+info: |
+  ECMAScript Standard Built-in Objects
+
+  Unless otherwise specified, the length property of a built-in
+  Function object has the attributes { [[Writable]]: false, [[Enumerable]]:
+  false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.prototype.drop, 'length', {
+  value: 1,
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/drop/limit-equals-total.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Removes entries from this iterator, specified by limit argument.
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 1;
+  yield 2;
+}
+
+let iterator = g().drop(2);
+let { value, done } = iterator.next();
+
+assert.sameValue(value, undefined);
+assert.sameValue(done, true);

test/built-ins/Iterator/prototype/drop/limit-greater-than-total.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Removes entries from this iterator, specified by limit argument.
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 1;
+  yield 2;
+}
+
+{
+  let iterator = g().drop(3);
+  let { value, done } = iterator.next();
+  assert.sameValue(value, undefined);
+  assert.sameValue(done, true);
+}
+
+{
+  let iterator = g().drop(Number.MAX_SAFE_INTEGER);
+  let { value, done } = iterator.next();
+  assert.sameValue(value, undefined);
+  assert.sameValue(done, true);
+}
+
+{
+  let iterator = g().drop(Infinity);
+  let { value, done } = iterator.next();
+  assert.sameValue(value, undefined);
+  assert.sameValue(done, true);
+}

test/built-ins/Iterator/prototype/drop/limit-less-than-total.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Removes entries from this iterator, specified by limit argument.
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 1;
+  yield 2;
+}
+
+let iterator = g().drop(1);
+
+{
+  let { value, done } = iterator.next();
+  assert.sameValue(value, 2);
+  assert.sameValue(done, false);
+}
+
+{
+  let { value, done } = iterator.next();
+  assert.sameValue(value, undefined);
+  assert.sameValue(done, true);
+}

test/built-ins/Iterator/prototype/drop/limit-rangeerror.js

@@ -0,0 +1,36 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Throws a RangeError exception when limit argument is NaN or less than 0.
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  3. If numLimit is NaN, throw a RangeError exception.
+  4. Let integerLimit be ! ToIntegerOrInfinity(numLimit).
+  5. If integerLimit < 0, throw a RangeError exception.
+
+features: [iterator-helpers]
+---*/
+let iterator = (function* () {})();
+
+iterator.drop(0);
+iterator.drop(-0.5);
+iterator.drop(null);
+
+assert.throws(RangeError, () => {
+  iterator.drop(-1);
+});
+
+assert.throws(RangeError, () => {
+  iterator.drop();
+});
+
+assert.throws(RangeError, () => {
+  iterator.drop(undefined);
+});
+
+assert.throws(RangeError, () => {
+  iterator.drop(NaN);
+});

test/built-ins/Iterator/prototype/drop/limit-tonumber-throws.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Throws a RangeError exception when limit argument valueOf throws.
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  2. Let numLimit be ? ToNumber(limit).
+
+features: [iterator-helpers]
+---*/
+let iterator = (function* () {})();
+
+assert.throws(Test262Error, () => {
+  iterator.drop({
+    valueOf: function () {
+      throw new Test262Error();
+    },
+  });
+});

test/built-ins/Iterator/prototype/drop/limit-tonumber.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Converts the limit argument to a Number using ToNumber and valueOf/toString.
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  2. Let numLimit be ? ToNumber(limit).
+
+features: [iterator-helpers]
+---*/
+function* g() {
+  yield 1;
+  yield 2;
+}
+
+{
+  let iterator = g();
+  let { value, done } = iterator
+    .drop({
+      valueOf: function () {
+        return 1;
+      },
+    })
+    .next();
+  assert.sameValue(value, 2);
+  assert.sameValue(done, false);
+}
+
+{
+  let iterator = g();
+  let { value, done } = iterator.drop([]).drop([1]).next();
+  assert.sameValue(value, 2);
+  assert.sameValue(done, false);
+}

test/built-ins/Iterator/prototype/drop/name.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  The "name" property of Iterator.prototype.drop
+info: |
+  17 ECMAScript Standard Built-in Objects
+
+  Every built-in Function object, including constructors, that is not
+  identified as an anonymous function has a name property whose value is a
+  String. Unless otherwise specified, this value is the name that is given to
+  the function in this specification.
+
+  ...
+
+  Unless otherwise specified, the name property of a built-in Function
+  object, if it exists, has the attributes { [[Writable]]: false,
+  [[Enumerable]]: false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.prototype.drop, 'name', {
+  value: 'drop',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/drop/next-method-returns-non-object.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator next returns non-object
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  6.b.ii. Let next be ? IteratorStep(iterated).
+
+  6.c.i. Let next be ? IteratorStep(iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class NonObjectIterator extends Iterator {
+  next() {
+    return null;
+  }
+}
+
+let iterator = new NonObjectIterator().drop(0);
+
+assert.throws(TypeError, function () {
+  iterator.next();
+});
+
+iterator = new NonObjectIterator().drop(2);
+
+assert.throws(TypeError, function () {
+  iterator.next();
+});

test/built-ins/Iterator/prototype/drop/next-method-returns-throwing-done.js

@@ -0,0 +1,41 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator next returns object with throwing done getter
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  6.b.ii. Let next be ? IteratorStep(iterated).
+
+  6.c.i. Let next be ? IteratorStep(iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  next() {
+    return {
+      get done() {
+        throw new Test262Error();
+      },
+      value: 1,
+    };
+  }
+  return() {
+    throw new Error();
+  }
+}
+
+let iterator = new ThrowingIterator().drop(0);
+
+assert.throws(Test262Error, function () {
+  iterator.next();
+});
+
+iterator = new ThrowingIterator().drop(1);
+
+assert.throws(Test262Error, function () {
+  iterator.next();
+});

test/built-ins/Iterator/prototype/drop/next-method-returns-throwing-value-done.js

@@ -0,0 +1,36 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator next returns object with throwing value getter, but is already done
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  6.c.ii. If next is false, return undefined.
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ReturnCalledError extends Error {}
+class ValueGetterError extends Error {}
+
+class ThrowingIterator extends Iterator {
+  next() {
+    return {
+      done: true,
+      get value() {
+        throw new ValueGetterError();
+      },
+    };
+  }
+  return() {
+    throw new ReturnCalledError();
+  }
+}
+
+let iterator = new ThrowingIterator().drop(0);
+iterator.next();
+
+iterator = new ThrowingIterator().drop(1);
+iterator.next();

test/built-ins/Iterator/prototype/drop/next-method-returns-throwing-value.js

@@ -0,0 +1,39 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator next returns object with throwing value getter
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  6.c.iii. Let completion be Completion(Yield(? IteratorValue(next))).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  next() {
+    return {
+      done: false,
+      get value() {
+        throw new Test262Error();
+      },
+    };
+  }
+  return() {
+    throw new Error();
+  }
+}
+
+let iterator = new ThrowingIterator().drop(0);
+
+assert.throws(Test262Error, function () {
+  iterator.next();
+});
+
+iterator = new ThrowingIterator().drop(1);
+
+assert.throws(Test262Error, function () {
+  iterator.next();
+});

test/built-ins/Iterator/prototype/drop/next-method-throws.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator has throwing next method
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  6.b.ii. Let next be ? IteratorStep(iterated).
+
+  6.c.i. Let next be ? IteratorStep(iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  next() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new ThrowingIterator().drop(0);
+
+assert.throws(Test262Error, function () {
+  iterator.next();
+});
+
+iterator = new ThrowingIterator().drop(1);
+
+assert.throws(Test262Error, function () {
+  iterator.next();
+});

test/built-ins/Iterator/prototype/drop/non-constructible.js

@@ -0,0 +1,28 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Iterator.prototype.drop is not constructible.
+
+  Built-in function objects that are not identified as constructors do not implement the [[Construct]] internal method unless otherwise specified in the description of a particular function.
+features: [iterator-helpers]
+---*/
+function* g() {}
+let iter = g();
+
+assert.throws(TypeError, () => {
+  new iter.drop();
+});
+
+assert.throws(TypeError, () => {
+  new iter.drop(0);
+});
+
+assert.throws(TypeError, () => {
+  new Iterator.prototype.drop(0);
+});
+
+assert.throws(TypeError, () => {
+  new class extends Iterator {}.drop(0);
+});

test/built-ins/Iterator/prototype/drop/prop-desc.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Property descriptor of Iterator.prototype.drop
+info: |
+  Iterator.prototype.drop
+
+  * is the initial value of the Iterator.prototype.drop property of the global object.
+
+  17 ECMAScript Standard Built-in Objects
+
+  Every other data property described in clauses 18 through 26 and in Annex B.2
+  has the attributes { [[Writable]]: true, [[Enumerable]]: false,
+  [[Configurable]]: true } unless otherwise specified.
+features: [globalThis, iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.prototype, 'drop', {
+  writable: true,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/drop/proto.js

@@ -0,0 +1,11 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  The value of the [[Prototype]] internal slot of Iterator.prototype.drop is the
+  intrinsic object %FunctionPrototype%.
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(Object.getPrototypeOf(Iterator.prototype.drop), Function.prototype);

test/built-ins/Iterator/prototype/drop/result-is-iterator.js

@@ -0,0 +1,11 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  The value of the [[Prototype]] internal slot of the return value of Iterator.prototype.drop is the
+  intrinsic object %IteratorHelperPrototype%.
+features: [iterator-helpers]
+---*/
+
+assert((function* () {})().drop(0) instanceof Iterator, 'function*(){}().drop(0) must return an Iterator');

test/built-ins/Iterator/prototype/drop/return-is-forwarded.js

@@ -0,0 +1,54 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator return is called when result iterator is closed
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  6.c.iii. Let completion be Completion(Yield(? IteratorValue(next))).
+  6.c.iv. IfAbruptCloseIterator(completion, iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let returnCount = 0;
+
+class TestIterator extends Iterator {
+  next() {
+    return {
+      done: false,
+      value: 1,
+    };
+  }
+  return() {
+    ++returnCount;
+    return {};
+  }
+}
+
+let iterator = new TestIterator().drop(0);
+assert.sameValue(returnCount, 0);
+iterator.return();
+assert.sameValue(returnCount, 1);
+iterator.return();
+assert.sameValue(returnCount, 1);
+
+returnCount = 0;
+
+iterator = new TestIterator().drop(1);
+assert.sameValue(returnCount, 0);
+iterator.return();
+assert.sameValue(returnCount, 1);
+iterator.return();
+assert.sameValue(returnCount, 1);
+
+returnCount = 0;
+
+iterator = new TestIterator().drop(1).drop(1).drop(1).drop(1).drop(1);
+assert.sameValue(returnCount, 0);
+iterator.return();
+assert.sameValue(returnCount, 1);
+iterator.return();
+assert.sameValue(returnCount, 1);

test/built-ins/Iterator/prototype/drop/return-is-not-forwarded-after-exhaustion.js

@@ -0,0 +1,50 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator return is not called after result iterator observes that underlying iterator is exhausted
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+let returnCount = 0;
+
+class TestIterator extends Iterator {
+  next() {
+    return {
+      done: true,
+      value: undefined,
+    };
+  }
+  return() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new TestIterator().drop(0);
+assert.throws(Test262Error, function () {
+  iterator.return();
+});
+iterator.next();
+iterator.return();
+
+iterator = new TestIterator().drop(1);
+iterator.next();
+iterator.return();
+
+iterator = new TestIterator().drop(1);
+assert.throws(Test262Error, function () {
+  iterator.return();
+});
+iterator.next();
+iterator.return();
+
+iterator = new TestIterator().drop(1).drop(1).drop(1).drop(1).drop(1);
+assert.throws(Test262Error, function () {
+  iterator.return();
+});
+iterator.next();
+iterator.return();

test/built-ins/Iterator/prototype/drop/this-non-callable-next.js

@@ -0,0 +1,19 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Iterator.prototype.drop throws TypeError when its this value is an object with a non-callable next
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iter = Iterator.prototype.drop.call({ next: 0 }, 1);
+
+assert.throws(TypeError, function () {
+  iter.next();
+});

test/built-ins/Iterator/prototype/drop/this-non-object.js

@@ -0,0 +1,34 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Iterator.prototype.drop throws TypeError when its this value is a non-object
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+assert.throws(TypeError, function () {
+  Iterator.prototype.drop.call(null, 1);
+});
+
+assert.throws(TypeError, function () {
+  Iterator.prototype.drop.call(null, {
+    valueOf: function () {
+      throw new Test262Error();
+    },
+  });
+});
+
+Object.defineProperty(Number.prototype, 'next', {
+  get: function () {
+    throw new Test262Error();
+  },
+});
+assert.throws(TypeError, function () {
+  Iterator.prototype.drop.call(0, 1);
+});

test/built-ins/Iterator/prototype/drop/this-plain-iterator.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Iterator.prototype.drop supports a this value that does not inherit from Iterator.prototype but implements the iterator protocol
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iter = {
+  get next() {
+    let count = 3;
+    return function () {
+      --count;
+      return count >= 0 ? { done: false, value: count } : { done: true, value: undefined };
+    };
+  },
+};
+
+let dropIter = Iterator.prototype.drop.call(iter, 1);
+
+let { done, value } = dropIter.next();
+
+assert.sameValue(done, false);
+assert.sameValue(value, 1);

test/built-ins/Iterator/prototype/drop/underlying-iterator-advanced-in-parallel.js

@@ -0,0 +1,39 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator is advanced after calling drop
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iterator = (function* () {
+  for (let i = 0; i < 5; ++i) {
+    yield i;
+  }
+})();
+
+let dropped = iterator.drop(2);
+
+let { value, done } = iterator.next();
+
+assert.sameValue(value, 0);
+assert.sameValue(done, false);
+
+({ value, done } = dropped.next());
+
+assert.sameValue(value, 3);
+assert.sameValue(done, false);
+
+({ value, done } = dropped.next());
+
+assert.sameValue(value, 4);
+assert.sameValue(done, false);
+
+({ value, done } = dropped.next());
+
+assert.sameValue(value, undefined);
+assert.sameValue(done, true);

test/built-ins/Iterator/prototype/drop/underlying-iterator-closed-in-parallel.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator is closed after calling drop
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iterator = (function* () {
+  for (let i = 0; i < 5; ++i) {
+    yield i;
+  }
+})();
+
+let dropped = iterator.drop(2);
+
+iterator.return();
+
+let { value, done } = dropped.next();
+
+assert.sameValue(value, undefined);
+assert.sameValue(done, true);

test/built-ins/Iterator/prototype/drop/underlying-iterator-closed.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.drop
+description: >
+  Underlying iterator is closed before calling drop
+info: |
+  %Iterator.prototype%.drop ( limit )
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iterator = (function* () {
+  for (let i = 0; i < 5; ++i) {
+    yield i;
+  }
+})();
+
+iterator.return();
+
+let dropped = iterator.drop(2);
+
+let { value, done } = dropped.next();
+
+assert.sameValue(value, undefined);
+assert.sameValue(done, true);

test/built-ins/Iterator/prototype/every/argument-effect-order.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Arguments and this value are evaluated in the correct order
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+includes: [compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+let effects = [];
+
+assert.throws(TypeError, function () {
+  Iterator.prototype.every.call(
+    {
+      get next() {
+        effects.push('get next');
+        return function () {
+          return { done: true, value: undefined };
+        };
+      },
+    },
+    null
+  );
+});
+
+assert.compareArray(effects, []);

test/built-ins/Iterator/prototype/every/callable.js

@@ -0,0 +1,13 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every is callable
+features: [iterator-helpers]
+---*/
+function* g() {}
+Iterator.prototype.every.call(g(), () => {});
+
+let iter = g();
+iter.every(() => {});

test/built-ins/Iterator/prototype/every/get-next-method-only-once.js

@@ -0,0 +1,38 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Gets the next method from the iterator only once
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let nextGets = 0;
+
+class TestIterator extends Iterator {
+  get next() {
+    ++nextGets;
+    let counter = 5;
+    return function () {
+      if (counter < 0) {
+        return { done: true, value: undefined };
+      } else {
+        return { done: false, value: --counter };
+      }
+    };
+  }
+}
+
+let iterator = new TestIterator();
+
+assert.sameValue(nextGets, 0);
+assert.sameValue(
+  iterator.every(() => true),
+  true
+);
+assert.sameValue(nextGets, 1);

test/built-ins/Iterator/prototype/every/get-next-method-throws.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator has throwing next getter
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class IteratorThrows extends Iterator {
+  get next() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new IteratorThrows();
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => {});
+});

test/built-ins/Iterator/prototype/every/get-return-method-throws.js

@@ -0,0 +1,31 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator has throwing return getter
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.f. If ToBoolean(result) is false, return ? IteratorClose(iterated, NormalCompletion(false)).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class IteratorThrows extends Iterator {
+  next() {
+    return {
+      done: false,
+      value: 0,
+    };
+  }
+  get return() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new IteratorThrows([1, 2]);
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => false);
+});

test/built-ins/Iterator/prototype/every/is-function.js

@@ -0,0 +1,10 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every is a built-in function
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(typeof Iterator.prototype.every, 'function');

test/built-ins/Iterator/prototype/every/iterator-already-exhausted.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every returns true when the iterator has already been exhausted
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.a. Let next be ? IteratorStep(iterated).
+  4.b. If next is false, return true.
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iterator = (function* () {})();
+
+let { value, done } = iterator.next();
+assert.sameValue(value, undefined);
+assert.sameValue(done, true);
+
+let result = iterator.every(() => true);
+assert.sameValue(result, true);
+
+result = iterator.every(() => false);
+assert.sameValue(result, true);

test/built-ins/Iterator/prototype/every/iterator-has-no-return.js

@@ -0,0 +1,27 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  The underlying iterator is sometimes unable to be closed (has no return method)
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iterator = [1, 2, 3, 4, 5][Symbol.iterator]();
+
+assert.sameValue(iterator.return, undefined);
+
+let ret = iterator.every(v => v < 4);
+
+assert.sameValue(ret, false);
+
+let { done, value } = iterator.next();
+assert.sameValue(done, false);
+assert.sameValue(value, 5);
+
+({ done, value } = iterator.next());
+assert.sameValue(done, true);
+assert.sameValue(value, undefined);

test/built-ins/Iterator/prototype/every/iterator-return-method-throws.js

@@ -0,0 +1,31 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator has throwing return
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.f. If ToBoolean(result) is false, return ? IteratorClose(iterated, NormalCompletion(false)).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class IteratorThrows extends Iterator {
+  next() {
+    return {
+      done: false,
+      value: 0,
+    };
+  }
+  return() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new IteratorThrows();
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => false);
+});

test/built-ins/Iterator/prototype/every/length.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every has a "length" property whose value is 1.
+info: |
+  ECMAScript Standard Built-in Objects
+
+  Unless otherwise specified, the length property of a built-in
+  Function object has the attributes { [[Writable]]: false, [[Enumerable]]:
+  false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.prototype.every, 'length', {
+  value: 1,
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/every/name.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  The "name" property of Iterator.prototype.every
+info: |
+  17 ECMAScript Standard Built-in Objects
+
+  Every built-in Function object, including constructors, that is not
+  identified as an anonymous function has a name property whose value is a
+  String. Unless otherwise specified, this value is the name that is given to
+  the function in this specification.
+
+  ...
+
+  Unless otherwise specified, the name property of a built-in Function
+  object, if it exists, has the attributes { [[Writable]]: false,
+  [[Enumerable]]: false, [[Configurable]]: true }.
+features: [iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.prototype.every, 'name', {
+  value: 'every',
+  writable: false,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/every/next-method-returns-non-object.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Underlying iterator next returns non-object
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.a. Let next be ? IteratorStep(iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class NonObjectIterator extends Iterator {
+  next() {
+    return null;
+  }
+}
+
+let iterator = new NonObjectIterator();
+
+assert.throws(TypeError, function () {
+  iterator.every(() => {});
+});

test/built-ins/Iterator/prototype/every/next-method-returns-throwing-done.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Underlying iterator next returns object with throwing done getter
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.a. Let next be ? IteratorStep(iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  next() {
+    return {
+      get done() {
+        throw new Test262Error();
+      },
+      value: 1,
+    };
+  }
+  return() {
+    throw new Error();
+  }
+}
+
+let iterator = new ThrowingIterator();
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => {});
+});

test/built-ins/Iterator/prototype/every/next-method-returns-throwing-value-done.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Underlying iterator next returns object with throwing value getter, but is already done
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.c. Let value be ? IteratorValue(next).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  next() {
+    return {
+      done: true,
+      get value() {
+        throw new Test262Error();
+      },
+    };
+  }
+  return() {
+    throw new Error();
+  }
+}
+
+let iterator = new ThrowingIterator();
+iterator.every(() => {});

test/built-ins/Iterator/prototype/every/next-method-returns-throwing-value.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Underlying iterator next returns object with throwing value getter
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.c. Let value be ? IteratorValue(next).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  next() {
+    return {
+      done: false,
+      get value() {
+        throw new Test262Error();
+      },
+    };
+  }
+  return() {
+    throw new Error();
+  }
+}
+
+let iterator = new ThrowingIterator();
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => {});
+});

test/built-ins/Iterator/prototype/every/next-method-throws.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Underlying iterator has throwing next method
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.a. Let next be ? IteratorStep(iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  next() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new ThrowingIterator();
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => {});
+});

test/built-ins/Iterator/prototype/every/non-callable-predicate.js

@@ -0,0 +1,22 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every expects to be called with a callable argument.
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  2. If IsCallable(predicate) is false, throw a TypeError exception.
+
+features: [iterator-helpers]
+flags: []
+---*/
+let nonCallable = {};
+let iterator = (function* () {
+  yield 1;
+})();
+
+assert.throws(TypeError, function () {
+  iterator.every(nonCallable);
+});

test/built-ins/Iterator/prototype/every/non-constructible.js

@@ -0,0 +1,28 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every is not constructible.
+
+  Built-in function objects that are not identified as constructors do not implement the [[Construct]] internal method unless otherwise specified in the description of a particular function.
+features: [iterator-helpers]
+---*/
+function* g() {}
+let iter = g();
+
+assert.throws(TypeError, () => {
+  new iter.every();
+});
+
+assert.throws(TypeError, () => {
+  new iter.every(() => {});
+});
+
+assert.throws(TypeError, () => {
+  new Iterator.prototype.every(() => {});
+});
+
+assert.throws(TypeError, () => {
+  new class extends Iterator {}.every(() => {});
+});

test/built-ins/Iterator/prototype/every/predicate-args.js

@@ -0,0 +1,43 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every predicate is passed the yielded value and a counter as arguments
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.d. Let result be Completion(Call(predicate, undefined, « value, 𝔽(counter) »)).
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 'a';
+  yield 'b';
+  yield 'c';
+}
+
+let iter = g();
+
+let assertionCount = 0;
+let result = iter.every((v, count) => {
+  switch (v) {
+    case 'a':
+      assert.sameValue(count, 0);
+      break;
+    case 'b':
+      assert.sameValue(count, 1);
+      break;
+    case 'c':
+      assert.sameValue(count, 2);
+      break;
+    default:
+      throw new Error();
+  }
+  ++assertionCount;
+  return true;
+});
+
+assert.sameValue(result, true);
+assert.sameValue(assertionCount, 3);

test/built-ins/Iterator/prototype/every/predicate-returns-falsey.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every returns false and closes the iterator when the predicate returns falsey immediately
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.f. If ToBoolean(result) is false, return ? IteratorClose(iterated, NormalCompletion(false)).
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 0;
+  yield 1;
+}
+
+let iter = g();
+
+let predicateCalls = 0;
+let result = iter.every(v => {
+  ++predicateCalls;
+  return false;
+});
+
+assert.sameValue(result, false);
+assert.sameValue(predicateCalls, 1);
+
+let { done, value } = iter.next();
+assert.sameValue(done, true);
+assert.sameValue(value, undefined);

test/built-ins/Iterator/prototype/every/predicate-returns-non-boolean.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every coerces predicate return value to boolean
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.f. If ToBoolean(result) is false, return ? IteratorClose(iterated, NormalCompletion(false)).
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  for (let i = 4; i >= 0; --i) {
+    yield i;
+  }
+}
+
+let iter = g();
+
+let predicateCalls = 0;
+let result = iter.every(v => {
+  ++predicateCalls;
+  return v;
+});
+
+assert.sameValue(result, false);
+assert.sameValue(predicateCalls, 5);

test/built-ins/Iterator/prototype/every/predicate-returns-truthy-then-falsey.js

@@ -0,0 +1,34 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every returns false and closes the iterator when the predicate returns truthy for some iterated values and falsey for others
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.f. If ToBoolean(result) is false, return ? IteratorClose(iterated, NormalCompletion(false)).
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  for (let i = 0; i < 5; ++i) {
+    yield i;
+  }
+}
+
+let iter = g();
+
+let predicateCalls = 0;
+let result = iter.every(v => {
+  ++predicateCalls;
+  return v < 3;
+});
+
+assert.sameValue(result, false);
+assert.sameValue(predicateCalls, 4);
+
+let { done, value } = iter.next();
+assert.sameValue(done, true);
+assert.sameValue(value, undefined);

test/built-ins/Iterator/prototype/every/predicate-returns-truthy.js

@@ -0,0 +1,24 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every returns true when the predicate returns truthy for all iterated values
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.b. If next is false, return true.
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 0;
+  yield 1;
+  yield 2;
+  yield 3;
+  yield 4;
+}
+
+let result = g().every(() => true);
+assert.sameValue(result, true);

test/built-ins/Iterator/prototype/every/predicate-this.js

@@ -0,0 +1,33 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every predicate this value is undefined
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.d. Let result be Completion(Call(predicate, undefined, « value, 𝔽(counter) »)).
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 0;
+}
+
+let iter = g();
+
+let expectedThis = function () {
+  return this;
+}.call(undefined);
+
+let assertionCount = 0;
+let result = iter.every(function (v, count) {
+  assert.sameValue(this, expectedThis);
+  ++assertionCount;
+  return true;
+});
+
+assert.sameValue(result, true);
+assert.sameValue(assertionCount, 1);

test/built-ins/Iterator/prototype/every/predicate-throws-then-closing-iterator-also-throws.js

@@ -0,0 +1,39 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Attempts to close iterator when predicate throws, but that throws
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.d. Let result be Completion(Call(predicate, undefined, « value, 𝔽(counter) »)).
+  4.e. IfAbruptCloseIterator(result, iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let returnCalls = 0;
+
+class TestIterator extends Iterator {
+  next() {
+    return {
+      done: false,
+      value: 1,
+    };
+  }
+  return() {
+    ++returnCalls;
+    throw new Error();
+  }
+}
+
+let iterator = new TestIterator();
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => {
+    throw new Test262Error();
+  });
+});
+
+assert.sameValue(returnCalls, 1);

test/built-ins/Iterator/prototype/every/predicate-throws.js

@@ -0,0 +1,43 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Closes iterator and throws when predicate throws
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  4.d. Let result be Completion(Call(predicate, undefined, « value, 𝔽(counter) »)).
+  4.e. IfAbruptCloseIterator(result, iterated).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let returnCalls = 0;
+
+class TestIterator extends Iterator {
+  next() {
+    return {
+      done: false,
+      value: 1,
+    };
+  }
+  return() {
+    ++returnCalls;
+    return {};
+  }
+}
+
+let iterator = new TestIterator();
+
+let callbackCalls = 0;
+
+assert.throws(Test262Error, function () {
+  iterator.every(() => {
+    ++callbackCalls;
+    throw new Test262Error();
+  });
+});
+
+assert.sameValue(callbackCalls, 1);
+assert.sameValue(returnCalls, 1);

test/built-ins/Iterator/prototype/every/prop-desc.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Property descriptor of Iterator.prototype.every
+info: |
+  Iterator.prototype.every
+
+  * is the initial value of the Iterator.prototype.every property of the global object.
+
+  17 ECMAScript Standard Built-in Objects
+
+  Every other data property described in clauses 18 through 26 and in Annex B.2
+  has the attributes { [[Writable]]: true, [[Enumerable]]: false,
+  [[Configurable]]: true } unless otherwise specified.
+features: [globalThis, iterator-helpers]
+includes: [propertyHelper.js]
+---*/
+
+verifyProperty(Iterator.prototype, 'every', {
+  writable: true,
+  enumerable: false,
+  configurable: true,
+});

test/built-ins/Iterator/prototype/every/proto.js

@@ -0,0 +1,11 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  The value of the [[Prototype]] internal slot of Iterator.prototype.every is the
+  intrinsic object %Function%.
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(Object.getPrototypeOf(Iterator.prototype.every), Function.prototype);

test/built-ins/Iterator/prototype/every/result-is-boolean.js

@@ -0,0 +1,11 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every returns a boolean
+features: [iterator-helpers]
+---*/
+function* g() {}
+let iter = g();
+assert.sameValue(typeof iter.every(() => {}), 'boolean');

test/built-ins/Iterator/prototype/every/this-non-callable-next.js

@@ -0,0 +1,17 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every throws TypeError when its this value is an object with a non-callable next
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+assert.throws(TypeError, function () {
+  Iterator.prototype.every.call({ next: 0 }, () => true);
+});

test/built-ins/Iterator/prototype/every/this-non-object.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every throws TypeError when its this value is a non-object
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+assert.throws(TypeError, function () {
+  Iterator.prototype.every.call(null, () => {});
+});
+
+Object.defineProperty(Number.prototype, 'next', {
+  get: function () {
+    throw new Test262Error();
+  },
+});
+assert.throws(TypeError, function () {
+  Iterator.prototype.every.call(0, () => {});
+});

test/built-ins/Iterator/prototype/every/this-plain-iterator.js

@@ -0,0 +1,32 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.every
+description: >
+  Iterator.prototype.every supports a this value that does not inherit from Iterator.prototype but implements the iterator protocol
+info: |
+  %Iterator.prototype%.every ( predicate )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let iter = {
+  get next() {
+    let count = 3;
+    return function () {
+      --count;
+      return count >= 0 ? { done: false, value: count } : { done: true, value: undefined };
+    };
+  },
+};
+
+let predicateCalls = 0;
+let result = Iterator.prototype.every.call(iter, function (v) {
+  ++predicateCalls;
+  return v;
+});
+
+assert.sameValue(result, false);
+assert.sameValue(predicateCalls, 3);

test/built-ins/Iterator/prototype/filter/argument-effect-order.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.filter
+description: >
+  Arguments and this value are evaluated in the correct order
+info: |
+  %Iterator.prototype%.filter ( predicate )
+
+includes: [compareArray.js]
+features: [iterator-helpers]
+flags: []
+---*/
+let effects = [];
+
+assert.throws(TypeError, function () {
+  Iterator.prototype.filter.call(
+    {
+      get next() {
+        effects.push('get next');
+        return function () {
+          return { done: true, value: undefined };
+        };
+      },
+    },
+    null
+  );
+});
+
+assert.compareArray(effects, []);

test/built-ins/Iterator/prototype/filter/callable.js

@@ -0,0 +1,13 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.filter
+description: >
+  Iterator.prototype.filter is callable
+features: [iterator-helpers]
+---*/
+function* g() {}
+Iterator.prototype.filter.call(g(), () => false);
+
+let iter = g();
+iter.filter(() => false);

test/built-ins/Iterator/prototype/filter/exhaustion-does-not-call-return.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.filter
+description: >
+  Underlying iterator return is not called when result iterator is exhausted
+info: |
+  %Iterator.prototype%.filter ( predicate )
+
+  3.b.i. Let next be ? IteratorStep(iterated).
+  3.b.ii. If next is false, return undefined.
+
+features: [iterator-helpers]
+flags: []
+---*/
+function* g() {
+  yield 0;
+  yield 1;
+  yield 2;
+}
+
+class TestIterator extends Iterator {
+  get next() {
+    let n = g();
+    return function() {
+      return n.next();
+    };
+  }
+  return() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new TestIterator().filter(() => false);
+iterator.next();
+iterator.next();
+iterator.next();

test/built-ins/Iterator/prototype/filter/get-next-method-only-once.js

@@ -0,0 +1,41 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.filter
+description: >
+  Gets the next method from the underlying iterator only once
+info: |
+  %Iterator.prototype%.filter ( predicate )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+let nextGets = 0;
+let nextCalls = 0;
+
+class CountingIterator extends Iterator {
+  get next() {
+    ++nextGets;
+    let iter = (function* () {
+      for (let i = 1; i < 5; ++i) {
+        yield i;
+      }
+    })();
+    return function () {
+      ++nextCalls;
+      return iter.next();
+    };
+  }
+}
+
+let iterator = new CountingIterator();
+
+assert.sameValue(nextGets, 0);
+assert.sameValue(nextCalls, 0);
+
+for (const value of iterator.filter(() => false));
+
+assert.sameValue(nextGets, 1);
+assert.sameValue(nextCalls, 5);

test/built-ins/Iterator/prototype/filter/get-next-method-throws.js

@@ -0,0 +1,25 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.filter
+description: >
+  Underlying iterator has throwing next getter
+info: |
+  %Iterator.prototype%.filter ( predicate )
+
+  1. Let iterated be ? GetIteratorDirect(this value).
+
+features: [iterator-helpers]
+flags: []
+---*/
+class ThrowingIterator extends Iterator {
+  get next() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new ThrowingIterator();
+
+assert.throws(Test262Error, function () {
+  iterator.filter(() => false);
+});

test/built-ins/Iterator/prototype/filter/get-return-method-throws.js

@@ -0,0 +1,30 @@
+// Copyright (C) 2023 Michael Ficarra. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.filter
+description: >
+  Underlying iterator return is throwing getter
+info: |
+  %Iterator.prototype%.filter ( predicate )
+
+features: [iterator-helpers]
+flags: []
+---*/
+class TestIterator extends Iterator {
+  next() {
+    return {
+      done: false,
+      value: 1,
+    };
+  }
+  get return() {
+    throw new Test262Error();
+  }
+}
+
+let iterator = new TestIterator().filter(() => true);
+iterator.next();
+
+assert.throws(Test262Error, function () {
+  iterator.return();
+});

test/built-ins/Iterator/prototype/filter/is-function.js

@@ -0,0 +1,10 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-iteratorprototype.filter
+description: >
+  Iterator.prototype.filter is a built-in function
+features: [iterator-helpers]
+---*/
+
+assert.sameValue(typeof Iterator.prototype.filter, 'function');