sindresorhus/eslint-plugin-unicorn

Rule proposal: No computed object property existence check

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#1,096 opened on Feb 5, 2021

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help wantednew rule

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Description

If property name is a variable, this may leads to unexpected result.

Fail

if (foo[bar]) {}

if (bar in foo) {}

In these cases if bar is 'toString', 'constructor' etc, it will be true.

Pass

if (foo[bar] === true) {}

if (Object.prototype.hasOwnProperty.call(foo, bar)) {}

Problem: foo maybe an array, static check can't know.

Idea from https://github.com/prettier/prettier/pull/10256

Contributor guide

Research direction
Review the ESLint custom rule API, then implement a rule that detects computed property existence checks with variables. Use AST selectors to find MemberExpression (computed: true) where the property is an Identifier, and also BinaryExpression with 'in' operator where the left side is an Identifier. Write tests with fail/pass cases.
Tech stack
javascriptnodejs
Domain
tooling
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaScriptESLintGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70