Array.from fails with Set on IE11

On IE11 (on Windows 10, if that’s important), when Array.from is passed a set, the Array.from polyfill is failing to detect the set. This appears to be an issue with the order in which polyfills are being loaded:

• Array.from first captures the Set.size property descriptor using Object.getOwnPropertyDescriptor(Set.prototype, ‘size’).get
• Then the Set polyfill kicks in and defines a new Set.size prototype using Object.defineProperty(Set.prototype, ‘size’, {

Placing a breakpoint in the Array.from polyfill’s isSet function, you can see that:

• executing setSize.call(set) throws an exception
• executing Object.getOwnPropertyDescriptor(Set.prototype, 'size').get.call(set) succeeds
• Object.getOwnPropertyDescriptor(Set.prototype, 'size').get === setSize is false

In other words, using an uncaptured value for the Set.prototype.size.get function succeeds, but using the previously captured value fails. So it looks like Array.from is capturing IE11’s native Set.size.get function, but then later trying to invoke the polyfilled version and throwing an exception as a result.

Here’s what the service is loading

UA detected: ie/11.0.0
Features requested: Array.prototype.@@iterator,Array.prototype.find,Array.prototype.includes,IntersectionObserver,Promise,Symbol,WeakMap,default,fetch,matchMedia,navigator.sendBeacon

Earlier resolutions

``` Object.assign, License: CC0 (required by "default", "_Iterator", "_ArrayIterator", "Array.prototype.@@iterator", "Array.from") Symbol, License: MIT (required by "Map", "default", "Set", "Symbol.iterator", "Array.prototype.@@iterator", "Symbol.species", "_Iterator", "_ArrayIterator", "Array.from", "Symbol.toStringTag") Symbol.iterator, License: MIT (required by "Array.prototype.@@iterator", "Map", "default", "Set", "_Iterator", "_ArrayIterator", "Array.from") Symbol.toStringTag, License: MIT (required by "_Iterator", "_ArrayIterator", "Array.prototype.@@iterator", "Array.from", "default") _Iterator, License: MIT (required by "_ArrayIterator", "Array.prototype.@@iterator", "Array.from", "default") Object.setPrototypeOf, License: MIT (required by "_ArrayIterator", "Array.prototype.@@iterator", "Array.from", "default") String.prototype.includes, License: CC0 (required by "default", "String.prototype.contains", "_ArrayIterator", "Array.prototype.@@iterator", "Array.from") String.prototype.contains, License: CC0 (required by "_ArrayIterator", "Array.prototype.@@iterator", "Array.from", "default") _ArrayIterator, License: MIT (required by "Array.prototype.@@iterator", "Array.from", "default") Array.prototype.@@iterator, License: CC0 Array.prototype.find, License: CC0 Array.prototype.includes, License: CC0 Event, License: CC0 (required by "default", "IntersectionObserver", "CustomEvent", "XMLHttpRequest", "fetch", "navigator.sendBeacon") IntersectionObserver, License: CC0 Promise, License: MIT (required by "default", "fetch") WeakMap, License: https://github.com/webcomponents/webcomponentsjs/blob/master/LICENSE.md fetch, License: MIT navigator.sendBeacon, License: MIT Number.isFinite, License: MIT (required by "Array.from", "default") ```

Number.isNaN, License: MIT (required by "default", "Array.from", "Map", "Set")
Array.from, License: CC0 (required by "default")
Array.of, License: MIT (required by "default")

followed by

``` Array.prototype.fill, License: CC0 (required by "default") CustomEvent, License: CC0 (required by "default") _DOMTokenList, License: CC0 (required by "DOMTokenList", "default") DOMTokenList, License: CC0 (required by "default") _mutation, License: CC0 (required by "DocumentFragment.prototype.append", "default", "DocumentFragment.prototype.prepend", "Element.prototype.after", "Element.prototype.append", "Element.prototype.before", "Element.prototype.prepend", "Element.prototype.remove", "Element.prototype.replaceWith") DocumentFragment.prototype.append, License: CC0 (required by "default") DocumentFragment.prototype.prepend, License: CC0 (required by "default") Element.prototype.after, License: CC0 (required by "default") Element.prototype.append, License: CC0 (required by "default") Element.prototype.before, License: CC0 (required by "default") Element.prototype.matches, License: CC0 (required by "default", "Element.prototype.closest") Element.prototype.closest, License: CC0 (required by "default") Element.prototype.prepend, License: CC0 (required by "default") Element.prototype.remove, License: CC0 (required by "default") Element.prototype.replaceWith, License: CC0 (required by "default") Symbol.species, License: MIT (required by "Map", "default", "Set") Map, License: CC0 (required by "default") Node.prototype.contains, License: CC0 (required by "default") ```

Set, License: CC0 (required by "default")
String.prototype.endsWith, License: CC0 (required by "default")
String.prototype.startsWith, License: CC0 (required by "default")
URL, License: CC0 (required by "default")

[Vazerthon]

Just come accross this issue when trying to create an array of unique items like so:

const toUniqueArray = array => [...new Set(array)];

A simple fix that works in IE11 and doesn’t cause problems in other browsers is to replace the above with:

const toUniqueArray = array => [...new Set(array).values()];

I’d guess (but haven’t tested) that this would work with Array.from as well.

[JakeChampion]

Hi all, this looks to have been fixed in a recent release. Here is a screenshot of it working in IE11 using the code Array.from(new Set([1,2,3])).