setPrototypeOf not supported in IE9 - IE10

The config for Object.setPrototypeOf refers to support for IEs 9-11 (https://github.com/Financial-Times/polyfill-service/blob/master/polyfills/Object/setPrototypeOf/config.json), but the source repo refers to IE 11+ (https://github.com/paulmillr/es6-shim/blame/master/README.md#L78) – and indeed am finding errors using IE10 that boil down to the fill behaving incorrectly and causing incorrect inheritance behaviour in babel-transpiled code. (FYI Babel works around not having the setPrototypeOf method present.)

My workaround (for anyone else hitting the same issue) is to add excludes=Object.setPrototypeOf to my polyfill URL (so I’m not getting a bad fill added), and add import "core-js/fn/object/set-prototype-of"; early in my code (so that I do have a fill for compatible browsers). This works okay so far.

I’m thinking that the fix here is to not fill setPrototypeOf for IE < 11, but I would imagine lots of other fills are relying on it… happy to submit a PR once steered!

[ejulianova]

Hey @JakeChampion, I have the same issue. Here’s a codepen where you can repro it in IE9/10: https://codepen.io/anon/pen/JpQQMq

Looks like Object.getPrototypeOf(Bar)) doesn’t return what we expect and the parent constructor never gets called. Note that the code is preprocessed with babel to the following:

function _possibleConstructorReturn(self, call) { if (!self) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return call && (typeof call === "object" || typeof call === "function") ? call : self; }

function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function, not " + typeof superClass); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, enumerable: false, writable: true, configurable: true } }); if (superClass) Object.setPrototypeOf ? Object.setPrototypeOf(subClass, superClass) : subClass.__proto__ = superClass; }

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

var Foo = function Foo(options) {
  _classCallCheck(this, Foo);

  console.log('[Foo] constructor called', options);
  this.options = options;
  this.someOption = options.someOption;
};

var Bar = function (_Foo) {
  _inherits(Bar, _Foo);

  function Bar(options) {
    _classCallCheck(this, Bar);

    var _this = _possibleConstructorReturn(this, (Bar.__proto__ || Object.getPrototypeOf(Bar)).call(this, options));

    console.log('[Bar] constructor called', options);
    console.log(_this.someOption);
    return _this;
  }

  return Bar;
}(Foo);

var bar = new Bar({ someOption: { blabla: 123 } });

It works when setPrototypeOf polyfill is excluded, because babel does the following: if (superClass) Object.setPrototypeOf ? Object.setPrototypeOf(subClass, superClass) : subClass.__proto__ = superClass;

[shauns]

@kentcdodds I exclude it, and then manually reimport directly from core-js to make sure IE11 and similar have it. I do wonder if the fix for this is just to set the expected browser range here to match that of the underlying polyfill.