sindresorhus/eslint-plugin-unicorn

Rule proposal: Forbid reassign top level variable in functions

Closed

#1,092 opened on Jan 30, 2021

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 (6 comments) (1 reaction) (0 assignees)JavaScript (468 forks)user submission
help wantednew rule

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Description

It's dangerous, and maybe get unexpected result when refactoring. In following example, if we change foo to async, or inside foo somehow reenter foo, cache may got change.

Fail

let cache; 

function foo() {
	cache = {};
	// ...
}

export default foo;

Pass

function foo() {
	let cache;

	// ...
}

Contributor guide

Research direction
Examine the existing ESLint rule implementations in the eslint plugin unicorn repository, particularly simple rules that forbid specific patterns. Use the ESLint RuleTester for testing. The rule should prevent reassignment of let or var variables declared at the top level of a module, only when inside a function. Look at AST selectors to target AssignmentExpression inside FunctionDeclaration or ArrowFunctionExpression that assign to a variable declared in Program scope. Include tests for both fail and pass cases as outlined in the issue.
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.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
ESLintJavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65