Update SubmitEvent Polyfill to Workaround Safari 15 bug

[terracatta]

Fixes #390

This PR updates the Polyfill to work around the Safari 15 bug where the submitter property is sometimes null when a form is submitted with element of type button vs an element of type submit. More info https://bugs.webkit.org/show_bug.cgi?id=229660

[terracatta]

@dhh ok I manually tested the broken behavior using Safari 15 with yarn start and I can confirm this fixes the issue with the least amount of required changes.

[terracatta]

cc @ParamagicDev since you use a similar polyfill for your mrujs project.

[KonnorRogers]

Thank you @terracatta , making a note on Mrujs so I can hotfix this.

[dhh]

Do we need any additional verification that this didn’t break other browsers handling it? Will this automatically become irrelevant when safari is fixed or does it require a change then?

[terracatta]

@dhh

Do we need any additional verification that this didn’t break other browsers handling it?

I don't think so.

First, the way it's written I only run a new behavior if it's Safari (via testing the navigator.vendor property) and Safari says it supports SubmitEvent.

Second, I've been running my ES6 polyfill on a high-traffic app that generates exceptions for console errors, and I am not seeing any regression in browsers that were already working fine.

Will this automatically become irrelevant when safari is fixed or does it require a change then?

So I downloaded the latest Safari Technical Preview Release 132 (Safari 15.4, WebKit 16613.1.1.5) which according to the release notes, has the underlying bug fixed (which I verified using the test case attached to the original Safari bug report). On this version, the polyfill still runs (even though it doesn't need to) but it doesn't do anything bad like throw errors/warnings or regress the behavior we want.

I cannot think of a clean way to test if we are on the fixed version of Safari without actually creating a fake form that produces the bug, submitting it via JS, preventing default, and checking the value of submitter. This might be possible, but I'm not sure if the juice is worth the squeeze.

[dhh]

Great work. Let’s put a note to revisit this in 3 months or whatever and hope that the version in the wild no longer is a meaningful percentage so we can clean this up 👍

[KonnorRogers]

Silly question, since Safari on iOS is probably similar to desktop Safari, is there a chance this will need to be fixed when iOS 15 ships?

[KonnorRogers]

Appears navigator.vendor can only be one of:
"Google Inc.", "Apple Computer Inc.", or ""

So I think we should be okay (you also tested it as well, thank you!)