Iterator#windows implementation

slowcheetah · zloirock · commit cf6aa2c6116d · 2025-06-04T00:02:44.000+03:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -37,9 +37,10 @@
   - Added built-ins:
     - `Iterator.zip`
     - `Iterator.zipKeyed`
-- [`Iterator` chunking stage 2 proposal](https://github.com/tc39/proposal-iterator-chunking):
+- Added [`Iterator` chunking stage 2 proposal](https://github.com/tc39/proposal-iterator-chunking):
   - Added built-ins:
     - `Iterator.prototype.chunks`
+    - `Iterator.prototype.windows`
 - [`Number.prototype.clamp` proposal](https://github.com/tc39/proposal-math-clamp):
   - Built-ins:
     - `Number.prototype.clamp`
diff --git a/README.md b/README.md
@@ -3060,22 +3060,26 @@ core-js(-pure)/full/symbol/custom-matcher
 ```
 
 ##### [`Iterator` chunking](https://github.com/tc39/proposal-iterator-chunking)[⬆](#index)
-Modules [`esnext.iterator.chunks`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.iterator.chunks.js)
+Modules [`esnext.iterator.chunks`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.iterator.chunks.js) and [`esnext.iterator.windows`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.iterator.windows.js)
 ```ts
 class Iterator {
   chunks(chunkSize: number): Iterator<any>;
+  windows(windowSize: number): Iterator<any>;
 }
 ```
 [*CommonJS entry points:*](#commonjs-api)
 ```
 core-js/proposals/iterator-chunking
 core-js(-pure)/full/iterator/chunks
+core-js(-pure)/full/iterator/windows
 ```
-[*Examples*](http://es6.zloirock.ru/#const%20digits%20%3D%20()%20%3D%3E%20%5B0%2C%201%2C%202%2C%203%2C%204%2C%205%2C%206%2C%207%2C%208%2C%209%5D.values()%3B%0A%0Alet%20chunksOf2%20%3D%20Array.from(digits().chunks(2))%3B%0A%0Alog(chunksOf2)%3B)
+[*Examples*](https://tinyurl.com/ypmzafjc)
 ```js
 const digits = () => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].values();
 
 let chunksOf2 = Array.from(digits().chunks(2));  // [ [0, 1], [2, 3], [4, 5], [6, 7], [8, 9] ]
+
+let windowsOf2 = Array.from(digits().windows(2));  // [ [0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [8, 9] ]
 ```
 
 #### Stage 1 proposals[⬆](#index)
diff --git a/packages/core-js-compat/src/data.mjs b/packages/core-js-compat/src/data.mjs
@@ -2488,6 +2488,8 @@ export const data = {
   'esnext.iterator.to-array': null,
   'esnext.iterator.to-async': {
   },
+  'esnext.iterator.windows': {
+  },
   'esnext.iterator.zip': {
   },
   'esnext.iterator.zip-keyed': {
diff --git a/packages/core-js/full/iterator/chunks.js b/packages/core-js/full/iterator/chunks.js
@@ -1,5 +1,8 @@
 'use strict';
+require('../../modules/es.object.to-string');
+require('../../modules/es.iterator.constructor');
 require('../../modules/esnext.iterator.chunks');
-var path = require('../../internals/path');
 
-module.exports = path.Iterator.chunks;
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('Iterator', 'chunks');
diff --git a/packages/core-js/full/iterator/index.js b/packages/core-js/full/iterator/index.js
@@ -3,6 +3,7 @@ var parent = require('../../actual/iterator');
 require('../../modules/esnext.iterator.chunks');
 require('../../modules/esnext.iterator.concat');
 require('../../modules/esnext.iterator.range');
+require('../../modules/esnext.iterator.windows');
 require('../../modules/esnext.iterator.zip');
 require('../../modules/esnext.iterator.zip-keyed');
 // TODO: Remove from `core-js@4`
diff --git a/packages/core-js/full/iterator/windows.js b/packages/core-js/full/iterator/windows.js
@@ -0,0 +1,8 @@
+'use strict';
+require('../../modules/es.object.to-string');
+require('../../modules/es.iterator.constructor');
+require('../../modules/esnext.iterator.windows');
+
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('Iterator', 'windows');
diff --git a/packages/core-js/modules/esnext.iterator.chunks.js b/packages/core-js/modules/esnext.iterator.chunks.js
@@ -12,8 +12,9 @@ var push = uncurryThis([].push);
 var IteratorProxy = createIteratorProxy(function () {
   var iterator = this.iterator;
   var next = this.next;
-  var result, done;
+  var chunkSize = this.chunkSize;
   var buffer = [];
+  var result, done;
   while (true) {
     result = anObject(call(next, iterator));
     done = !!result.done;
@@ -23,7 +24,7 @@ var IteratorProxy = createIteratorProxy(function () {
       return;
     }
     push(buffer, result.value);
-    if (buffer.length === this.chunkSize) return buffer;
+    if (buffer.length === chunkSize) return buffer;
   }
 });
 
diff --git a/packages/core-js/modules/esnext.iterator.windows.js b/packages/core-js/modules/esnext.iterator.windows.js
@@ -0,0 +1,45 @@
+'use strict';
+var $ = require('../internals/export');
+var anObject = require('../internals/an-object');
+var call = require('../internals/function-call');
+var createIteratorProxy = require('../internals/iterator-create-proxy');
+var getIteratorDirect = require('../internals/get-iterator-direct');
+var uncurryThis = require('../internals/function-uncurry-this');
+
+var $RangeError = RangeError;
+var push = uncurryThis([].push);
+var slice = uncurryThis([].slice);
+
+var IteratorProxy = createIteratorProxy(function () {
+  var iterator = this.iterator;
+  var next = this.next;
+  var buffer = this.buffer;
+  var windowSize = this.windowSize;
+  var result, done;
+  while (true) {
+    result = anObject(call(next, iterator));
+    done = this.done = !!result.done;
+    if (done) return;
+
+    push(buffer, result.value);
+    if (buffer.length === windowSize) {
+      this.buffer = slice(buffer, 1);
+      return buffer;
+    }
+  }
+});
+
+// `Iterator.prototype.windows` method
+// https://github.com/tc39/proposal-iterator-chunking
+$({ target: 'Iterator', proto: true, real: true, forced: true }, {
+  windows: function windows(windowSize) {
+    var O = anObject(this);
+    if (!windowSize || windowSize >>> 0 !== windowSize) {
+      throw $RangeError('windowSize must be integer in [1, 2^32-1]');
+    }
+    return new IteratorProxy(getIteratorDirect(O), {
+      windowSize: windowSize,
+      buffer: []
+    });
+  }
+});
diff --git a/packages/core-js/proposals/iterator-chunking.js b/packages/core-js/proposals/iterator-chunking.js
@@ -1,3 +1,4 @@
 'use strict';
 // https://github.com/tc39/proposal-iterator-chunking
 require('../modules/esnext.iterator.chunks');
+require('../modules/esnext.iterator.windows');
diff --git a/tests/compat/tests.js b/tests/compat/tests.js
@@ -1836,7 +1836,6 @@ GLOBAL.tests = {
     return Function.prototype[Symbol.metadata] === null;
   },
   'esnext.iterator.chunks': function () {
-    // eslint-disable-next-line es/no-nonstandard-iterator-prototype-properties -- required for detection
     return Iterator.prototype.chunks;
   },
   'esnext.iterator.concat': function () {
@@ -1848,6 +1847,9 @@ GLOBAL.tests = {
   'esnext.iterator.to-async': function () {
     return Iterator.prototype.toAsync;
   },
+  'esnext.iterator.windows': function () {
+    return Iterator.prototype.windows;
+  },
   'esnext.iterator.zip': function () {
     return Iterator.zip;
   },
diff --git a/tests/entries/unit.mjs b/tests/entries/unit.mjs
@@ -773,6 +773,8 @@ for (PATH of ['core-js-pure', 'core-js']) {
     ok(typeof load(NS, 'iterator/indexed') == 'function');
     ok(load(NS, 'iterator/concat')([2]).next().value === 2);
     ok(load(NS, 'iterator/range')(1, 2).next().value === 1);
+    ok(typeof load(NS, 'iterator/chunks') == 'function');
+    ok(typeof load(NS, 'iterator/windows') == 'function');
     ok(typeof load(NS, 'iterator/zip') == 'function');
     ok(typeof load(NS, 'iterator/zip-keyed') == 'function');
     ok(load(NS, 'map/delete-all')(new Map(), 1, 2) === false);
@@ -1104,7 +1106,6 @@ for (const NS of ['full', 'features']) {
   load(NS, 'typed-array/filter-reject');
   load(NS, 'typed-array/group-by');
   load(NS, 'typed-array/unique-by');
-  load(NS, 'iterator/chunks');
 }
 
 load('modules/esnext.string.at-alternative');
diff --git a/tests/eslint/eslint.config.js b/tests/eslint/eslint.config.js
@@ -1256,6 +1256,7 @@ const forbidCompletelyNonExistentBuiltIns = {
     'asIndexedPairs',
     'indexed',
     'chunks',
+    'windows',
   ] }],
   'es/no-nonstandard-json-properties': [ERROR, { allow: [
     'isRawJSON',
diff --git a/tests/unit-global/esnext.iterator.windows.js b/tests/unit-global/esnext.iterator.windows.js
@@ -0,0 +1,35 @@
+import { createIterator } from '../helpers/helpers.js';
+
+const { from } = Array;
+
+QUnit.test('Iterator#windows', assert => {
+  const { windows } = Iterator.prototype;
+
+  assert.isFunction(windows);
+  assert.arity(windows, 1);
+  assert.name(windows, 'windows');
+  assert.looksNative(windows);
+  assert.nonEnumerable(Iterator.prototype, 'windows');
+
+  assert.arrayEqual(from(windows.call(createIterator([1, 2, 3]), 2)), [[1, 2], [2, 3]], 'basic functionality #1');
+  assert.arrayEqual(from(windows.call(createIterator([1, 2, 3, 4]), 2)), [[1, 2], [2, 3], [3, 4]], 'basic functionality #2');
+  assert.arrayEqual(from(windows.call(createIterator([]), 2)), [], 'basic functionality on empty iterable');
+
+  const it = createIterator([1, 2, 3]);
+  const result = windows.call(it, 3);
+  assert.isIterable(result, 'returns iterable');
+  assert.isIterator(result, 'returns iterator');
+  assert.true(result instanceof Iterator, 'returns iterator');
+  assert.deepEqual(result.next(), { done: false, value: [1, 2, 3] }, '.next with active inner iterator result');
+  assert.deepEqual(result.return(), { done: true, value: undefined }, '.return with active inner iterator result');
+  assert.deepEqual(result.next(), { done: true, value: undefined }, '.return with active inner iterator result on closed iterator');
+
+  assert.throws(() => windows.call('', 1), TypeError, 'iterable non-object this');
+  assert.throws(() => windows.call(undefined, 1), TypeError, 'non-iterable-object this #1');
+  assert.throws(() => windows.call(null, 1), TypeError, 'non-iterable-object this #2');
+  assert.throws(() => windows.call(5, 1), TypeError, 'non-iterable-object this #3');
+
+  assert.throws(() => windows.call(it), RangeError, 'throws on empty argument');
+  assert.throws(() => windows.call(it, -1), RangeError, 'throws on negative argument');
+  assert.throws(() => windows.call(it, 0x100000000), RangeError, 'throws on argument more then 2^32 - 1');
+});
diff --git a/tests/unit-pure/esnext.iterator.windows.js b/tests/unit-pure/esnext.iterator.windows.js
@@ -0,0 +1,34 @@
+import { createIterator } from '../helpers/helpers.js';
+
+import Iterator from 'core-js-pure/full/iterator/index';
+import from from 'core-js-pure/es/array/from';
+
+QUnit.test('Iterator#windows', assert => {
+  const { windows } = Iterator.prototype;
+  assert.isFunction(windows);
+  assert.arity(windows, 1);
+  assert.name(windows, 'windows');
+  assert.nonEnumerable(Iterator.prototype, 'windows');
+
+  assert.arrayEqual(from(windows.call(createIterator([1, 2, 3]), 2)), [[1, 2], [2, 3]], 'basic functionality #1');
+  assert.arrayEqual(from(windows.call(createIterator([1, 2, 3, 4]), 2)), [[1, 2], [2, 3], [3, 4]], 'basic functionality #2');
+  assert.arrayEqual(from(windows.call(createIterator([]), 2)), [], 'basic functionality on empty iterable');
+
+  const it = createIterator([1, 2, 3]);
+  const result = windows.call(it, 3);
+  assert.isIterable(result, 'returns iterable');
+  assert.isIterator(result, 'returns iterator');
+  assert.true(result instanceof Iterator, 'returns iterator');
+  assert.deepEqual(result.next(), { done: false, value: [1, 2, 3] }, '.next with active inner iterator result');
+  assert.deepEqual(result.return(), { done: true, value: undefined }, '.return with active inner iterator result');
+  assert.deepEqual(result.next(), { done: true, value: undefined }, '.return with active inner iterator result on closed iterator');
+
+  assert.throws(() => windows.call('', 1), TypeError, 'iterable non-object this');
+  assert.throws(() => windows.call(undefined, 1), TypeError, 'non-iterable-object this #1');
+  assert.throws(() => windows.call(null, 1), TypeError, 'non-iterable-object this #2');
+  assert.throws(() => windows.call(5, 1), TypeError, 'non-iterable-object this #3');
+
+  assert.throws(() => windows.call(it), RangeError, 'throws on empty argument');
+  assert.throws(() => windows.call(it, -1), RangeError, 'throws on negative argument');
+  assert.throws(() => windows.call(it, 0x100000000), RangeError, 'throws on argument more then 2^32 - 1');
+});
