Echo JS 0.11.0

Neither the original article, or the polyfill references any proposal to add this to the EcmaScript spec.  And there's no reference to this on MozDev.

It's definitely a cool method, that said, I would suggest *NOT* doing a polyfill unless or until this is an actual EcmaScript proposal at Stage 1 at the very least.  It's not really a polyfill, because it's not filling any actual spec at any stage.  It's a non-standard extension.

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Edit, would also copy/paste this on the blog itself, but they want permission to "Act on my behalf" in Github which is a non-starter and ridiculous permission to ask for.

"Neither the original article [...] references any proposal to add this to the EcmaScript spec."

Plain wrong. Please go read the post again. It mentions: "Fortunately, a new proposal https://github.com/tc39/proposal-relative-indexing-method (at stage 3 as of January 2021) brings the method at() to arrays."

"but they want permission to "Act on my behalf" in Github"

Please go read about https://utteranc.es/ commenting system. "Act on my behalf" means that you allow Utterances app to comment in GitHub issues, but only in repositories that have installed Utterances app.

The article links to the polyfill... and the polyfill is under es-shims ... but I didn't see a link to the proposal you linked to in the above comment, which I would suggest adding/linking towards the top.

   Array.at(index) (proposal)  <-- link there

I had searched via google, mozdev and caniuse and wasn't able to find the actual proposal/spec.
edit: https://github.com/es-shims/Array.prototype.at/pull/2

I usually comment with the specific proposal specification on these types of articles as it's usually missing or incomplete.  Often, I'll also add the babel transform/polyfill for reference.

The permission itself doesn't seem to display, or define any restrictions in particular.