Report useless check when accessing array elements in `no-useless-undefined`

描述

const foo = index >= 0 ? array[index] : undefined;
const foo = index < 0 ? undefined : array[index];

const foo = index <= array.length - 1 ? array[index] : undefined;
const foo = index > array.length - 1 ? undefined : array[index];

const foo = index >= 5 ? array[index - 5] : undefined;

const foo = array[index];

const foo = index >= 0 ? array[index] : bar;

贡献者指南

技术栈

javascriptnodejs

领域

developer experiencetooling

议题类型

feature

难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。

3

预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。

1-3 hours

活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。

fresh

清晰度议题是否清楚说明期望改动、验收标准和下一步。

mostly clear

前置要求

basic JavaScriptunderstanding of ESLint rulesfamiliarity with no useless undefined rule

新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。

60

研究方向

First, examine the existing `no useless undefined` rule implementation in `rules/no useless undefined.js` to understand its logic. Then, decide whether to extend this rule or create a new one based on the maintainer's feedback (the issue author is uncertain). Implement detection of patterns where an array element access (e.g., `array[index]`) is guarded by a ternary with `undefined` on one branch, which could be replaced by just the access. The fix should handle various comparisons like `>=0`, `<0`, `<=array.length 1`, etc. Refer to the linked issue in the comment for discussion.