Add `ArrayAt` type for stricter `Array.prototype.at()` with tuples

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Description

const tuple = ['abc', 123, true] as const;

type First = ArrayAt<typeof tuple, 0>; // 'abc'
type Last = ArrayAt<typeof tuple, -1>; // true
type SecondToLast = ArrayAt<typeof tuple, -2>; // 123
type ThirdToLast = ArrayAt<typeof tuple, -3>; // 'abc'
type OutOfBounds = ArrayAt<typeof tuple, 999>; // should not compile since 999 does not extend 0 | 1 | 2 | -1 | -2 | -3

const array = ['abc', 123, true];

type First = ArrayAt<typeof tuple, 0>; // string | number | true
type Last = ArrayAt<typeof tuple, -1>; // string | number | true
type OutOfBounds = ArrayAt<typeof tuple, 999>; // string | number | true

Contributor guide

Research direction

Study TypeScript's conditional types, infer, and tuple indexing. Look at existing similar types in the library like `LastArrayElement` or `TupleOf`. Understand how to constrain index types using `keyof` on tuples and handle negative indices by converting them to positive offsets.

Tech stack

typescript

Domain

full stack

Issue type

Feature

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

4

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

Half day

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Active

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

Clear

Prerequisites

TypeScriptGit

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

30