[DOM Reference] Update CustomEvent interface reference

[teoli2003]

This is part of #9740.

• All properties and methods of CustomEventare documented in the modern format.
• All are listed in the interface.
• I removed a polyfill for pre-IE9 browsers
• I removed some information about the security risks of using this in privileged code.

[github-actions]

Preview URLs

• https://pr9920.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/CustomEvent/CustomEvent
• https://pr9920.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/CustomEvent/detail
• https://pr9920.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/CustomEvent/initCustomEvent
• https://pr9920.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/CustomEvent

Flaws

None! 🎉

External URLs

URL: /en-US/docs/Web/API/CustomEvent
Title: CustomEvent
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/CustomEvent/CustomEvent
Title: CustomEvent()
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/CustomEvent/initCustomEvent
Title: CustomEvent.initCustomEvent()
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/CustomEvent/detail
Title: CustomEvent.detail
on GitHub

No new external URLs

(this comment was updated 2021-11-22 10:05:08.024309)

[teoli2003]

Thanks a lot, @jpmedley! This is very helpful.

[jpmedley]

This is important enough that it should be at the top, not in what many may view as extra information.

(Has anyone discussed whether deprecated features should have a heading titled "Alternatives"?)

[teoli2003]

It is already mentioned in the first section, at the top of the article, in the note:

I think it does no harm to have it at both places, and I 100% agree it has to be mentioned at the top.

For an Alternatives, it is worth discussing. I don't know if we want a heading or a note, but we definitively need the information about the alternative (and near the top of the article) each time something is deprecated or non-standard, or people will continue to use it.

[jpmedley]

I think it does no harm to have it at both places

One such item does no harm. I do my best to minimize such repetitions. They are too easily missed during update passes.

lgtm

[joshuakimrub]

Hello,
a few weeks ago I was doing some research on possible security issues in CustomEvents when I came across the "Firing from privileged code to non-privileged code" in your documentation. Now I am wondering why it has been removed in this commit. Has this security risk been resolved or just moved to another page and I just overlooked it?
Best regards,
Joshua

[Elchi3]

It was removed because the section talked about Firefox XUL/XPCOM extension code. We are trying to make MDN Web Docs only about Web technologies. XUL/XPCOM Firefox extensions don't exist anymore so it was removed for that reason. "privileged" referred to privileged code in an extension context.
I hope this clears it up?

[joshuakimrub]

Yes, thank you very much!