A syntax approach (arr[^n] for arr[arr.length-n])

[caub]

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• more powerful (one syntax for many cases: arr[^1], arr[^2], etc.. or arr[~1] if this symbol is chosen)
• more portable (it could apply to strings, we could use or not a protocol Symbol.index, I'm not sure it's needed, less spec additions is better)
• more readable (similar to git shortcuts, C# also has a similar syntax, etc.)
• no web compat risks
• less complexity added (this proposal adds lastIndex and lastItem) and prototypes 'pollution', so a symtax approach is more future-proof in that aspect maybe?
• goes well with another stage1 proposal slice-notation or slice-expression as it could be renamed, it was mentioned in https://github.com/tc39/proposal-slice-notation/issues/19#issuecomment-523375691

[ljharb]

Syntax seems like a pretty high cost for something that's only useful on arrays and arraylike objects.

[hax]

We can't use arr[~n] because it's already a valid expression 😂 (~1 === -2)

[caub]

Yes true, so we're left with arr[^1]

[Fenzland]

why not just use negative number arr[-1], ^n may be used as a new unary operator like ~n some day.

[ljharb]

@Fenzland because var o = { '-1': true } and var a = []; a['-1'] = 'not the last item'; are things that can already exist.