145155 2015-05-18 17:48:56 -0700 ES6 classes: Subclassing arrays doesn't work 2020-03-10 15:31:31 -0700 1 1 1 Unclassified WebKit JavaScriptCore 528+ (Nightly build) All All RESOLVED DUPLICATE 152706 P2 Normal --- 1 nvasilyev webkit-unassigned ashvayka richardconnamacher oldest_to_newest 1095762 0 nvasilyev 2015-05-18 17:48:56 -0700 var MyArray = class MyArray extends Array { constructor(len) { super(len); } myMethod() {} }; var myArr = new MyArray(0); console.log(myArr.myMethod); // 'function' in Chrome 42+, undefined in WebKit ToT console.log(myArr instanceof MyArray); // true in Chrome 42+, false in WebKit ToT myArr.push(1); console.log(myArr instanceof MyArray); // true in Chrome 42+, false in WebKit ToT 1145634 1 richardconnamacher 2015-12-02 11:13:57 -0800 WebKit isn't setting the right prototype chain when instantiating an Array subclass. Because of this, the following workaround restores the correct behavior in the WebKit nightly: var MyArray = class MyArray extends Array { constructor() { super(...arguments); Object.setPrototypeOf(this, new.target.prototype); } myMethod() {} }; 1153989 2 richardconnamacher 2016-01-08 13:39:57 -0800 This appears to have been fixed in the latest WebKit nightly (as of 1/8/2016) 1628406 3 ashvayka 2020-03-10 15:31:31 -0700 Fixed in https://trac.webkit.org/changeset/194612. Tests: JSTests/ChakraCore/test/es6/classes.js JSTests/ChakraCore/test/es6/ES6SubclassableBuiltins.js JSTests/es6/Array_is_subclassable_*.js JSTests/test262/test/language/statements/class/subclass/builtin-objects/Array/*.js *** This bug has been marked as a duplicate of bug 152706 ***