React-hook-form and polyfill.io causing page to crash Z.current.unMount is not iterable

Question

React-hook-form and polyfill.io causing page to crash Z.current.unMount is not iterable.

To re-create:

On IE11 you can go to polyfill.io and download the minified code. Or simply paste this into IE11 https://polyfill.io/v3/polyfill.min.js and you will get the required code. Create a React project and create a basic form using React-form-hook. Next import the polyfill and this will result in the page crashing: Z.current.unMount is not iterable. As soon as you remove the polyfill the form works as expected.

Background:

These polyfill's/ponyfill's are needed as still supporting IE11... yeah... we use polyfill.io to get the required polyfills. We load this polyfill on every page. Wondering if anyone else has come across this issue usig polyfills and react-hook-form and has a good work around?

This issue seems to have come from version 6.8.4 of React-hook-form and above.

Without polyfill

With polyfill - This error is inside of the React-form-hook library

Answer 1

We ran into this problem too, and discovered like you that polyfill was the issue. I'm not sure if our issue is exactly the same, because we've only just seen this issue show up, while you reported this issue 4 months ago. That leads me to think our issues are not the same, but posting just in case.

What seems to be happening for us is that when you use the polyfill service but don't specify a version, sometimes the js file you get back contains js content, and sometimes doesn't (try the url in your browser with a hard refresh). In our case, I'm assuming that the case where it does not return a js bundle is the desired behaviour because the browser doesn't need any polyfilling.

Specifying a version for the file seems to fix the issue for us. Doesn't seem to matter what version, just specifying a version itself seems to ensure that it returns the correct bundle content every time. E.g.:

https://polyfill.io/v3/polyfill.min.js?version=3.110.1

Have posted a bug report here: https://github.com/Financial-Times/polyfill-service/issues/2699