Adding at() docs

[Rumyra]

Adding array.at(), string.at() and typedarray.at() pages.

Looking at a review as these are actually my first js ref docs... some notes:

• Live samples won't work until this pr is merged https://github.com/mdn/interactive-examples/pull/1753/files (not sure why tests are failing)
• Note BCD data is not yet in
• Not sure what to reference in the way of spec which is here https://tc39.es/proposal-relative-indexing-method/

tl:dr; please review but don't merge until I've resolved above :) @chrisdavidmills

[sideshowbarker]

Nits

[chrisdavidmills]

Hi @Rumyra !

I'm just preparing for the Fx 85 launch and giving this a review as part of it.

Looks mostly good. Any nitpicks I find I'll make directly to the text and not both you with them.

A few points to help you with the remainder:

• Looks like BCD still needs merging (just commented it). You might as well as the macro calls to thesepages now, so they are ready.
• You also need an entry in the Experimental features page, as this isn't in the release version yet.
• For the Spec, you need to use "ESNext — see https://github.com/mdn/yari/blob/master/kumascript/macros/SpecData.json#L777"

Can you make this a priority? The launch of Fx 85 is in 8 days. Thanks!

[Rumyra]

I've updated the spec links and bcd... one thing is the at method is not in the draft spec yet 😬 I've added what should be the link...

[chrisdavidmills]

one thing is the at method is not in the draft spec yet 😬 I've added what should be the link...

Hrm, this makes me wonder whether we shouldn't just link to the draft proposal instead for now.

@Elchi3 , what would you do here? at() is currently only specified at https://tc39.es/proposal-relative-indexing-method/, and not in the ESDraft spec yet, so we are not sure what to do about the spec link.

[Rumyra]

Let me know - I'll update here if it needs changing 👍

[Elchi3]

This is great! Happy to see you contributing to JS ref docs. I've reviewed this some more and left comments on the Array.prototype.at page for you, but they also apply to the other two methods mostly.

[Rumyra]

Converting to draft until I've done feedbacks

[Elchi3]

Great stuff! Some nits and I think we're good to go.