A call to the setDescriptor function fails in IE11.

Bug

What

A call to the setDescriptor function fails in IE11.

Details

In IE11 (user-agent: ‘Mozilla/5.0 (Windows NT 10.0; WOW64; Trident/7.0; Touch; rv:11.0) like Gecko’), under certain circumstances (reasons not known), the ‘protoDescriptor’ variable in the setDescriptor function (line 4842) is undefined. This means the call to objectDefineProperty fails.

The solution is to change code as follows:

setDescriptor = function (o, key, descriptor) {
  var protoDescriptor = gOPD(ObjectProto, key);
  delete ObjectProto[key];
  objectDefineProperty(o, key, descriptor);
  if (o !== ObjectProto) {
    objectDefineProperty(ObjectProto, key, protoDescriptor);
  }
};

to:

setDescriptor = function (o, key, descriptor) {
  var protoDescriptor = gOPD(ObjectProto, key);
  delete ObjectProto[key];
  objectDefineProperty(o, key, descriptor);
  if (o !== ObjectProto && protoDescriptor !== undefined) {
    objectDefineProperty(ObjectProto, key, protoDescriptor);
  }
};

[RaParker]

Yes. Sorry, I’ve meant to get back to you for a week now.

So, it turned out there were two polyfills running: core-js and this one. The problem is that for IE11, core-js doesn’t provide nearly enough polyfilling. I did try manually creating an extract of the missing prototype definitions, copied directly from your library, but once these errors were resolved, some obscure errors remained. So for the time being, I’ve resigned myself to running two polyfills for ie11 alone, but applying the manual fix I described in the initial bug report. It’s far from an ideal scenario, but it does work, so I’m going with that.

On Sun, 22 Aug 2021 at 08:38, Romain Menke @.***> wrote:

@RaParker https://github.com/RaParker did you find anything interesting?

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/Financial-Times/polyfill-library/issues/1072#issuecomment-903227533, or unsubscribe https://github.com/notifications/unsubscribe-auth/AELRFYR557W7AY3BINOOUSLT6CSO3ANCNFSM5AVZ5TCA . Triage notifications on the go with GitHub Mobile for iOS https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675 or Android https://play.google.com/store/apps/details?id=com.github.android&utm_campaign=notification-email .

[JakeChampion]

Thanks for looking into this both of you. That Babel plugin looks great!