Iterator cannot be polyfilled in Safari (up to 18)

[CreativeTechGuy]

When using a polyfill which depends on Iterator such as

const m = new Map();
m.keys().map(() => {}); // <- `.map` is from the Iterator protocol

As of Safari 18, it doesn't support most of the Iterator protocol. But the polyfill attempts to augment the globalThis["Iterator"] prototype, which doesn't exist in Safari (despite the compat chart saying it should). So the polyfill despite being loaded doesn't initialize and no-op.

I don't know if there is any way that this can be fixed in core-js so that these Iterator polyfills work in Safari. At the very least I hope this issue will help others not run into this.

[zloirock]

core-js is being tested in Safari 18 in CI and regularly manually, and everything works fine.

That could happen if for any reason you missed the import of es.iterator.constructor module.

[zloirock]

You could report it here https://github.com/babel/babel-polyfills

Current definitions here look fine, as an option - you use an obsolete @babel/preset-env / babel-plugin-polyfill-corejs3 version.

[CreativeTechGuy]

Actually, I just double checked and @babel/preset-env is showing that esnext.iterator.constructor is being included along with esnext.iterator.map. I was only stepping through the iterator map polyfill to see why it might not be working, but now I'll step through the iterator constructor polyfill to see why it might not be doing anything.

[zloirock]

Actually, I just double checked and @babel/preset-env is showing that esnext.iterator.constructor is being included along with esnext.iterator.map. I was only stepping through the iterator map polyfill to see why it might not be working, but now I'll step through the iterator constructor polyfill to see why it might not be doing anything.

In this case, please, add a reproducible example.

[CreativeTechGuy]

And I just checked versions and I'm using [email protected] and @babel/[email protected], so not the latest, but pretty close.

And yes I'll get a minimal reproducible example for you later today. Thank you so much for your help and all of the work you do!

[zloirock]

babel-plugin-polyfill-corejs3 had a related issue in definitions that was fixed recently, babel/babel-polyfills#223, so make sure that you use the latest versions of all those packages.

[CreativeTechGuy]

Repro is here: https://github.com/CreativeTechGuy/core-js-safari-iterator-repro

Let me know if there's anything else I can do to make this easier. I tried to use the very least amount of config/code/dependencies to make it super straight forward.

[zloirock]

@CreativeTechGuy your example contains [email protected] with the mentioned related bug. It was fixed in 0.11.0. It seems it is still not updated in the published @babel/preset-env. You could ask for it in their repo.

[CreativeTechGuy]

Thank you! It's always frustrating when a new version that fixes a problem is released but not yet consumed where it's used. I'll go ask for it.