sindresorhus/eslint-plugin-unicorn

Rule proposal: `prefer-iterator-to-array`

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#2,567 opened on Feb 20, 2025

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 (2 comments) (3 reactions) (0 assignees)JavaScript (5,022 stars) (468 forks)user submission
help wantednew rule

Description

Description

Iterator#toArray() is more clear to me that coverts iterator to array than [...iterator], especially when iterator is a long expression.

Examples

// ❌
[...map.values()].map(value => value * 2)

// ✅
map.values().toArray().map(value => value * 2)
map.values().map(value => value * 2).toArray()

Proposed rule name

prefer-iterator-to-array

Additional Info

Full list of Iterators https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator#description

Contributor guide

Tech stack
javascripttypescript
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.
half day
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 plugin developmentAST basicsJavaScript iterators
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Review the implementation of similar rules like 'prefer array flat map' in the eslint plugin unicorn repository for code patterns. The rule needs to detect spread operator usage on iterables (e.g., [...map.values()]) and suggest using .toArray() instead. Use AST selectors like 'SpreadElement' or 'CallExpression' to identify the pattern. The issue provides clear examples of what should be flagged and what should be preferred.