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.