Iterator#sliding implementation

slowcheetah · slowcheetah · commit 2e84cd6521b0 · 2025-07-02T21:51:43.000+07:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -5,6 +5,7 @@
 - Fixed some cases of `Set.prototype.{ symmetricDifference, union }` detection
 - Added missing dependencies to some entries of static `Iterator` methods
 - Added missing `/full/{ instance, number/virtual }/clamp` entries
+- Added `sliding` method to `Iterator` chunking stage 2 proposal
 - Compat data improvements:
   - Added Electron 38 compat data mapping
   - `Iterator` helpers marked as fixed and updated following the latest spec changes in Safari 26.0
diff --git a/README.md b/README.md
@@ -3059,25 +3059,30 @@ 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) and [`esnext.iterator.windows`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.iterator.windows.js)
+Modules [`esnext.iterator.chunks`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.iterator.chunks.js), [`esnext.iterator.sliding`](https://github.com/zloirock/core-js/blob/master/packages/core-js/modules/esnext.iterator.sliding.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>;
+  sliding(windowSize: 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/sliding
 core-js(-pure)/full/iterator/windows
 ```
-[*Examples*](https://tinyurl.com/ypmzafjc)
+[*Examples*](https://tinyurl.com/24xnkcnn)
 ```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 slidingOf2 = Array.from(digits().sliding(2));  // [ [0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 7], [7, 8], [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] ]
 ```
 
diff --git a/packages/core-js-compat/src/data.mjs b/packages/core-js-compat/src/data.mjs
@@ -2484,6 +2484,8 @@ export const data = {
   },
   // TODO: Remove from `core-js@4`
   'esnext.iterator.reduce': null,
+  'esnext.iterator.sliding': {
+  },
   // TODO: Remove from `core-js@4`
   'esnext.iterator.some': null,
   // TODO: Remove from `core-js@4`
diff --git a/packages/core-js-compat/src/modules-by-versions.mjs b/packages/core-js-compat/src/modules-by-versions.mjs
@@ -299,4 +299,7 @@ export default {
     'esnext.iterator.zip-keyed',
     'esnext.number.clamp',
   ],
+  3.44: [
+    'esnext.iterator.sliding',
+  ],
 };
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.sliding');
 require('../../modules/esnext.iterator.windows');
 require('../../modules/esnext.iterator.zip');
 require('../../modules/esnext.iterator.zip-keyed');
diff --git a/packages/core-js/full/iterator/sliding.js b/packages/core-js/full/iterator/sliding.js
@@ -0,0 +1,8 @@
+'use strict';
+require('../../modules/es.object.to-string');
+require('../../modules/es.iterator.constructor');
+require('../../modules/esnext.iterator.sliding');
+
+var entryUnbind = require('../../internals/entry-unbind');
+
+module.exports = entryUnbind('Iterator', 'sliding');
diff --git a/packages/core-js/modules/esnext.iterator.sliding.js b/packages/core-js/modules/esnext.iterator.sliding.js
@@ -0,0 +1,46 @@
+'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 createIterResultObject = require('../internals/create-iter-result-object');
+var getIteratorDirect = require('../internals/get-iterator-direct');
+var iteratorClose = require('../internals/iterator-close');
+var uncurryThis = require('../internals/function-uncurry-this');
+
+var $RangeError = RangeError;
+var push = uncurryThis([].push);
+var slice = uncurryThis([].slice);
+
+var IteratorProxy = createIteratorProxy(function () {
+  var iterator = this.iterator;
+  var next = this.next;
+  var buffer = this.buffer;
+  var windowSize = this.windowSize;
+  var result, done;
+  while (true) {
+    result = anObject(call(next, iterator));
+    done = this.done = !!result.done;
+    if (done && buffer.length && buffer.length < windowSize) return createIterResultObject(buffer, false);
+    if (done) return createIterResultObject(undefined, true);
+
+    if (buffer.length === windowSize) this.buffer = buffer = slice(buffer, 1);
+    push(buffer, result.value);
+    if (buffer.length === windowSize) return createIterResultObject(buffer, false);
+  }
+}, false, true);
+
+// `Iterator.prototype.sliding` method
+// https://github.com/tc39/proposal-iterator-chunking/pull/21
+$({ target: 'Iterator', proto: true, real: true, forced: true }, {
+  sliding: function sliding(windowSize) {
+    var O = anObject(this);
+    if (typeof windowSize != 'number' || !windowSize || windowSize >>> 0 !== windowSize) {
+      return iteratorClose(O, 'throw', new $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
@@ -2,3 +2,4 @@
 // https://github.com/tc39/proposal-iterator-chunking
 require('../modules/esnext.iterator.chunks');
 require('../modules/esnext.iterator.windows');
+require('../modules/esnext.iterator.sliding');
diff --git a/tests/compat/tests.js b/tests/compat/tests.js
@@ -1844,6 +1844,9 @@ GLOBAL.tests = {
   'esnext.iterator.range': function () {
     return Iterator.range;
   },
+  'esnext.iterator.sliding': function () {
+    return Iterator.prototype.sliding;
+  },
   'esnext.iterator.to-async': function () {
     return Iterator.prototype.toAsync;
   },
diff --git a/tests/entries/unit.mjs b/tests/entries/unit.mjs
@@ -774,6 +774,7 @@ for (PATH of ['core-js-pure', 'core-js']) {
     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/sliding') == 'function');
     ok(typeof load(NS, 'iterator/windows') == 'function');
     ok(typeof load(NS, 'iterator/zip') == 'function');
     ok(typeof load(NS, 'iterator/zip-keyed') == 'function');
diff --git a/tests/eslint/eslint.config.js b/tests/eslint/eslint.config.js
@@ -1256,6 +1256,7 @@ const forbidCompletelyNonExistentBuiltIns = {
   ] }],
   'es/no-nonstandard-iterator-prototype-properties': [ERROR, { allow: [
     'chunks',
+    'sliding',
     'toAsync',
     'windows',
     // TODO: drop from `core-js@4`
diff --git a/tests/unit-global/esnext.iterator.sliding.js b/tests/unit-global/esnext.iterator.sliding.js
@@ -0,0 +1,48 @@
+import { STRICT } from '../helpers/constants.js';
+import { createIterator } from '../helpers/helpers.js';
+
+const { from } = Array;
+
+QUnit.test('Iterator#sliding', assert => {
+  const { sliding } = Iterator.prototype;
+
+  assert.isFunction(sliding);
+  assert.arity(sliding, 1);
+  assert.name(sliding, 'sliding');
+  assert.looksNative(sliding);
+  assert.nonEnumerable(Iterator.prototype, 'sliding');
+
+  assert.arrayEqual(from(sliding.call(createIterator([1, 2, 3]), 2)), [[1, 2], [2, 3]], 'basic functionality #1');
+  assert.arrayEqual(from(sliding.call(createIterator([1, 2, 3, 4]), 2)), [[1, 2], [2, 3], [3, 4]], 'basic functionality #2');
+  assert.arrayEqual(from(sliding.call(createIterator([1, 2]), 3)), [[1, 2]], 'basic functionality #3');
+  assert.arrayEqual(from(sliding.call(createIterator([]), 2)), [], 'basic functionality on empty iterable');
+
+  const it = createIterator([1, 2, 3]);
+  const result = sliding.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');
+
+  if (STRICT) {
+    assert.throws(() => sliding.call('', 1), TypeError, 'iterable non-object this');
+    assert.throws(() => sliding.call(undefined, 1), TypeError, 'non-iterable-object this #1');
+    assert.throws(() => sliding.call(null, 1), TypeError, 'non-iterable-object this #2');
+    assert.throws(() => sliding.call(5, 1), TypeError, 'non-iterable-object this #3');
+  }
+
+  assert.throws(() => sliding.call(it), RangeError, 'throws on empty argument');
+  assert.throws(() => sliding.call(it, -1), RangeError, 'throws on negative argument');
+
+  const observableReturn = {
+    return() {
+      this.called = true;
+      return { done: true, value: undefined };
+    },
+  };
+  const itObservable = createIterator([1, 2, 3], observableReturn);
+  assert.throws(() => sliding.call(itObservable, 0x100000000), RangeError, 'throws on argument more then 2^32 - 1');
+  assert.true(itObservable.called, 'iterator closed on argument validation error');
+});
diff --git a/tests/unit-global/esnext.iterator.windows.js b/tests/unit-global/esnext.iterator.windows.js
@@ -14,6 +14,7 @@ QUnit.test('Iterator#windows', assert => {
 
   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([1, 2]), 3)), [], 'basic functionality #3');
   assert.arrayEqual(from(windows.call(createIterator([]), 2)), [], 'basic functionality on empty iterable');
 
   const it = createIterator([1, 2, 3]);
diff --git a/tests/unit-pure/esnext.iterator.sliding.js b/tests/unit-pure/esnext.iterator.sliding.js
@@ -0,0 +1,47 @@
+import { STRICT } from '../helpers/constants.js';
+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#sliding', assert => {
+  const { sliding } = Iterator.prototype;
+  assert.isFunction(sliding);
+  assert.arity(sliding, 1);
+  assert.name(sliding, 'sliding');
+  assert.nonEnumerable(Iterator.prototype, 'sliding');
+
+  assert.arrayEqual(from(sliding.call(createIterator([1, 2, 3]), 2)), [[1, 2], [2, 3]], 'basic functionality #1');
+  assert.arrayEqual(from(sliding.call(createIterator([1, 2, 3, 4]), 2)), [[1, 2], [2, 3], [3, 4]], 'basic functionality #2');
+  assert.arrayEqual(from(sliding.call(createIterator([1, 2]), 3)), [[1, 2]], 'basic functionality #3');
+  assert.arrayEqual(from(sliding.call(createIterator([]), 2)), [], 'basic functionality on empty iterable');
+
+  const it = createIterator([1, 2, 3]);
+  const result = sliding.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');
+
+  if (STRICT) {
+    assert.throws(() => sliding.call('', 1), TypeError, 'iterable non-object this');
+    assert.throws(() => sliding.call(undefined, 1), TypeError, 'non-iterable-object this #1');
+    assert.throws(() => sliding.call(null, 1), TypeError, 'non-iterable-object this #2');
+    assert.throws(() => sliding.call(5, 1), TypeError, 'non-iterable-object this #3');
+  }
+
+  assert.throws(() => sliding.call(it), RangeError, 'throws on empty argument');
+  assert.throws(() => sliding.call(it, -1), RangeError, 'throws on negative argument');
+
+  const observableReturn = {
+    return() {
+      this.called = true;
+      return { done: true, value: undefined };
+    },
+  };
+  const itObservable = createIterator([1, 2, 3], observableReturn);
+  assert.throws(() => sliding.call(itObservable, 0x100000000), RangeError, 'throws on argument more then 2^32 - 1');
+  assert.true(itObservable.called, 'iterator closed on argument validation error');
+});
diff --git a/tests/unit-pure/esnext.iterator.windows.js b/tests/unit-pure/esnext.iterator.windows.js
@@ -13,6 +13,7 @@ QUnit.test('Iterator#windows', assert => {
 
   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([1, 2]), 3)), [], 'basic functionality #3');
   assert.arrayEqual(from(windows.call(createIterator([]), 2)), [], 'basic functionality on empty iterable');
 
   const it = createIterator([1, 2, 3]);
