fix handling of sparse arrays in structuredClone, close #1156

CHANGELOG.md

@@ -74,6 +74,7 @@
   - Added Samsung Internet 19.0 compat data mapping
   - Added Quest Browser 24.0 compat data mapping
   - Fixed the first version in the Chromium-based Edge compat data mapping
+- Fixed handling of sparse arrays in `structuredClone`, [#1156](https://github.com/zloirock/core-js/issues/1156)
 - `{ Map, WeakMap }.prototype.emplace` became stricter [by the spec draft](https://tc39.es/proposal-upsert/)
 - Fixed a theoretically possible future conflict of polyfills definitions in the pure version
 - Added pure version of the `Number` constructor, [#1154](https://github.com/zloirock/core-js/issues/1154), [#1155](https://github.com/zloirock/core-js/issues/1155), thanks [@trosos](https://github.com/trosos)

packages/core-js/modules/web.structured-clone.js

@@ -28,6 +28,7 @@ var IS_DENO = require('../internals/engine-is-deno');
 var IS_NODE = require('../internals/engine-is-node');
 
 var Object = global.Object;
+var Array = global.Array;
 var Date = global.Date;
 var Error = global.Error;
 var EvalError = global.EvalError;
@@ -153,7 +154,7 @@ var structuredCloneInternal = function (value, map) {
 
   switch (type) {
     case 'Array':
-      cloned = [];
+      cloned = Array(lengthOfArrayLike(value));
       deep = true;
       break;
     case 'Object':

tests/unit-global/web.structured-clone.js

@@ -239,6 +239,7 @@ QUnit.module('structuredClone', () => {
     const arrays = [
       [],
       [1, 2, 3],
+      Array(1),
       assign(
         ['foo', 'bar'],
         { 10: true, 11: false, 20: 123, 21: 456, 30: null }),

tests/unit-pure/web.structured-clone.js

@@ -247,6 +247,7 @@ QUnit.module('structuredClone', () => {
     const arrays = [
       [],
       [1, 2, 3],
+      Array(1),
       assign(
         ['foo', 'bar'],
         { 10: true, 11: false, 20: 123, 21: 456, 30: null }),