Getting nth-last item from an array

Rationale

Currently the only ways to get an element from the end of an Array is with the .length property:someArray[someArray.length - n] or using the .slice method: someArray.slice(-1)[0]

High Level Proposal

We propose to add the Symbol.index protocol to Array

Array.prototype[Symbol.index](n, fromEnd = false) { }

The existing someArray[n] desugars tosomeArray[Symbol.index](n)

The new proposed syntax someArray[^n] desugars to someArray[Symbol.index](n, true)

This protocol could be added to String as well

Specification

// TODO

Related proposal

Compared to https://github.com/keithamus/proposal-array-last, the benefit in our proposal is to:

• avoid any web-compatibility issue
• avoid "magic" getters
• have a more powerful and user-friendly syntax, similarly to https://github.com/tc39/proposal-slice-notation