`prefer-at` should also mark substrings of length 1

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Description

string.substring(0, 1)
string.substring(value, value + 1)
string.substring(value, 1 + value)
string.substring(value - 1, value)

string[0]
string[value]
string[value - 1]

string.at(0)
string.at(value)
string.at(value - 1)

string.charAt(0)
string.charAt(value)
string.charAt(value - 1)

Contributor guide

Research direction

The issue requests extending the existing `prefer at` rule to also flag `substring` calls where the length is 1. The implementation should detect calls like `string.substring(0, 1)` and suggest using bracket notation or `at()` or `charAt()`. The developer should look at the existing rule implementation in the repository (likely in `rules/prefer at.js`) to understand the pattern matching approach. The linked issue and comments provide examples of fail and pass cases. The fix requires adding a new check for `CallExpression` with callee `substring` and two arguments where the second argument is an addition or subtraction involving the first argument or a literal 1. Testing is also needed.

Tech stack

javascript

Domain

developer experience

Issue type

Feature

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

3

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

1-3 hours

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

Fresh

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

Clear

Prerequisites

ESLint rule developmentAST traversal

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

70