GeezerVison

Up.

This proposal has web combability problem so it's need to be renamed.

Well... tc39/proposal-relative-indexing-method#34

FYI, per the linked issue, item could not be used in ECMAScript due to web compatibility issues. See #40695 (comment)

The TypeScript team hasn't accepted the linked issue #40695. If you can get it accepted, this PR will have a better chance of being reviewed.

We discussed this in the design meeting and concluded:

1. at should return T | undefined, as this PR does.
2. The compiler should add support for negative indices on tuples, along with special support for at to work the same way. Something like

declare let t: [string, number]
let n = t.at(-1) // n: number
type TN = (typeof t)[-1] // also number?
// and perhaps even
declare let t2: [...string, number]
let n2 = t.at(-1)

Though the second example would require adding quite a bit more code to the checker.

I expect Daniel Rosenwasser (@DanielRosenwasser) will link the notes when he's done preparing them.

Ron Buckton (@rbuckton) Can you take another look and merge if all your comments have been addressed?

It looks like a different PR was merged that already addressed this: #46291