Echo JS 0.11.0

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.