Iterator is not constructible from the active function object (work…

…s as an abstract class)

CHANGELOG.md

@@ -9,8 +9,9 @@
 - [`Set` methods stage 3 proposal](https://github.com/tc39/proposal-set-methods), July 2023 TC39 meeting updates::
   - Throw on negative `Set` sizes, [proposal-set-methods/88](https://github.com/tc39/proposal-set-methods/pull/88)
   - Removed `IsCallable` check in `GetKeysIterator`, [proposal-set-methods/101](https://github.com/tc39/proposal-set-methods/pull/101)
-- [Iterator Helpers stage 3 proposal](https://github.com/tc39/proposal-iterator-helpers), July 2023 TC39 meeting updates::
-  - Avoid creating observable `String` wrapper objects, [proposal-iterator-helpers/281](https://github.com/tc39/proposal-iterator-helpers/pull/281)
+- [Iterator Helpers stage 3 proposal](https://github.com/tc39/proposal-iterator-helpers):
+  - Avoid creating observable `String` wrapper objects, July 2023 TC39 meeting update, [proposal-iterator-helpers/281](https://github.com/tc39/proposal-iterator-helpers/pull/281)
+  - `Iterator` is not constructible from the active function object (works as an abstract class)
 - Async explicit resource management:
   - Built-ins:
     - `Symbol.asyncDispose`

packages/core-js/modules/esnext.async-iterator.constructor.js

@@ -1,6 +1,7 @@
 'use strict';
 var $ = require('../internals/export');
 var anInstance = require('../internals/an-instance');
+var getPrototypeOf = require('../internals/object-get-prototype-of');
 var createNonEnumerableProperty = require('../internals/create-non-enumerable-property');
 var hasOwn = require('../internals/has-own-property');
 var wellKnownSymbol = require('../internals/well-known-symbol');
@@ -9,8 +10,11 @@ var IS_PURE = require('../internals/is-pure');
 
 var TO_STRING_TAG = wellKnownSymbol('toStringTag');
 
+var $TypeError = TypeError;
+
 var AsyncIteratorConstructor = function AsyncIterator() {
   anInstance(this, AsyncIteratorPrototype);
+  if (getPrototypeOf(this) === AsyncIteratorPrototype) throw $TypeError('Abstract class AsyncIterator not directly constructable');
 };
 
 AsyncIteratorConstructor.prototype = AsyncIteratorPrototype;

packages/core-js/modules/esnext.iterator.constructor.js

@@ -3,6 +3,7 @@ var $ = require('../internals/export');
 var global = require('../internals/global');
 var anInstance = require('../internals/an-instance');
 var isCallable = require('../internals/is-callable');
+var getPrototypeOf = require('../internals/object-get-prototype-of');
 var createNonEnumerableProperty = require('../internals/create-non-enumerable-property');
 var fails = require('../internals/fails');
 var hasOwn = require('../internals/has-own-property');
@@ -12,6 +13,7 @@ var IS_PURE = require('../internals/is-pure');
 
 var TO_STRING_TAG = wellKnownSymbol('toStringTag');
 
+var $TypeError = TypeError;
 var NativeIterator = global.Iterator;
 
 // FF56- have non-standard global helper `Iterator`
@@ -23,6 +25,7 @@ var FORCED = IS_PURE
 
 var IteratorConstructor = function Iterator() {
   anInstance(this, IteratorPrototype);
+  if (getPrototypeOf(this) === IteratorPrototype) throw $TypeError('Abstract class Iterator not directly constructable');
 };
 
 if (!hasOwn(IteratorPrototype, TO_STRING_TAG)) {

tests/unit-global/esnext.async-iterator.constructor.js

@@ -1,3 +1,5 @@
+import { nativeSubclass } from '../helpers/helpers';
+
 const { getPrototypeOf } = Object;
 
 QUnit.test('AsyncIterator', assert => {
@@ -22,7 +24,12 @@ QUnit.test('AsyncIterator', assert => {
   assert.true(AsyncIterator.from([1, 2, 3]) instanceof AsyncIterator, 'Async From Proxy');
   assert.true(AsyncIterator.from([1, 2, 3]).drop(1) instanceof AsyncIterator, 'Async Drop Proxy');
 
-  assert.true(new AsyncIterator() instanceof AsyncIterator, 'constructor');
+  if (nativeSubclass) {
+    const Sub = nativeSubclass(AsyncIterator);
+    assert.true(new Sub() instanceof AsyncIterator, 'abstract constructor');
+  }
+
+  assert.throws(() => new AsyncIterator(), 'direct constructor throws');
   assert.throws(() => AsyncIterator(), 'throws w/o `new`');
 });
 

tests/unit-global/esnext.async-iterator.from.js

@@ -1,4 +1,4 @@
-const { assign } = Object;
+const { assign, create } = Object;
 
 QUnit.test('AsyncIterator.from', assert => {
   const { from } = AsyncIterator;
@@ -13,7 +13,7 @@ QUnit.test('AsyncIterator.from', assert => {
 
   assert.true(AsyncIterator.from([]) instanceof AsyncIterator, 'proxy, iterable');
 
-  const asyncIterator = assign(new AsyncIterator(), {
+  const asyncIterator = assign(create(AsyncIterator.prototype), {
     next: () => { /* empty */ },
   });
 

tests/unit-global/esnext.iterator.constructor.js

@@ -1,4 +1,4 @@
-import { createIterator } from '../helpers/helpers';
+import { createIterator, nativeSubclass } from '../helpers/helpers';
 
 const { getPrototypeOf } = Object;
 
@@ -28,7 +28,12 @@ QUnit.test('Iterator', assert => {
   assert.true(Iterator.from(createIterator([1, 2, 3])) instanceof Iterator, 'From Proxy');
   assert.true([].values().drop(1) instanceof Iterator, 'Drop Proxy');
 
-  assert.true(new Iterator() instanceof Iterator, 'constructor');
+  if (nativeSubclass) {
+    const Sub = nativeSubclass(Iterator);
+    assert.true(new Sub() instanceof Iterator, 'abstract constructor');
+  }
+
+  assert.throws(() => new Iterator(), 'direct constructor throws');
   assert.throws(() => Iterator(), 'throws w/o `new`');
 });
 

tests/unit-pure/esnext.async-iterator.constructor.js

@@ -1,3 +1,5 @@
+import { nativeSubclass } from '../helpers/helpers';
+
 import Symbol from 'core-js-pure/es/symbol';
 
 import AsyncIterator from 'core-js-pure/actual/async-iterator';
@@ -9,7 +11,12 @@ QUnit.test('AsyncIterator', assert => {
   assert.true(AsyncIterator.from([1, 2, 3]) instanceof AsyncIterator, 'Async From Proxy');
   assert.true(AsyncIterator.from([1, 2, 3]).drop(1) instanceof AsyncIterator, 'Async Drop Proxy');
 
-  assert.true(new AsyncIterator() instanceof AsyncIterator, 'constructor');
+  if (nativeSubclass) {
+    const Sub = nativeSubclass(AsyncIterator);
+    assert.true(new Sub() instanceof AsyncIterator, 'abstract constructor');
+  }
+
+  assert.throws(() => new AsyncIterator(), 'direct constructor throws');
   assert.throws(() => AsyncIterator(), 'throws w/o `new`');
 });
 

tests/unit-pure/esnext.async-iterator.from.js

@@ -1,5 +1,6 @@
 import Promise from 'core-js-pure/es/promise';
 import assign from 'core-js-pure/es/object/assign';
+import create from 'core-js-pure/es/object/create';
 import values from 'core-js-pure/es/array/values';
 import AsyncIterator from 'core-js-pure/actual/async-iterator';
 
@@ -13,7 +14,7 @@ QUnit.test('AsyncIterator.from', assert => {
 
   assert.true(AsyncIterator.from([]) instanceof AsyncIterator, 'proxy, iterable');
 
-  const asyncIterator = assign(new AsyncIterator(), {
+  const asyncIterator = assign(create(AsyncIterator.prototype), {
     next: () => { /* empty */ },
   });
 

tests/unit-pure/esnext.iterator.constructor.js

@@ -1,4 +1,4 @@
-import { createIterator } from '../helpers/helpers';
+import { createIterator, nativeSubclass } from '../helpers/helpers';
 
 import Symbol from 'core-js-pure/es/symbol';
 import Iterator from 'core-js-pure/actual/iterator';
@@ -9,7 +9,12 @@ QUnit.test('Iterator', assert => {
 
   assert.true(Iterator.from(createIterator([1, 2, 3])) instanceof Iterator, 'From Proxy');
 
-  assert.true(new Iterator() instanceof Iterator, 'constructor');
+  if (nativeSubclass) {
+    const Sub = nativeSubclass(Iterator);
+    assert.true(new Sub() instanceof Iterator, 'abstract constructor');
+  }
+
+  assert.throws(() => new Iterator(), 'direct constructor throws');
   assert.throws(() => Iterator(), 'throws w/o `new`');
 });