sindresorhus/eslint-plugin-unicorn

Rule proposal: Disallow optional chaining on undeclared variables

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#1,479 opened on Aug 11, 2021

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help wantednew rule

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Description

It's unfortunate that ?. is sugar for x !== undefined and not typeof x !== 'undefined'. The subtle difference is that the first one will fail if x is not defined at all.

Would it make sense to disallow the operator unless the variable is in the scope?

Fail

iDontExist?.meNeither

Pass

globalThis.iDontExist?.meNeither

let iDontExist;
iDontExist?.meNeither

Contributor guide

Research direction
Investigate how ESLint rules detect undeclared variables and implement a rule that flags optional chaining on variables not defined in the current scope.
Tech stack
javascriptnodejs
Domain
toolingdeveloper 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.
Half day
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
JavaScriptESLint
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60