sindresorhus/eslint-plugin-unicorn

Rule proposal: `prefer-split-limit`

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#2,464 opened on Oct 3, 2024

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help wantednew rule

Description

Description

Whenever we use String.prototype.split with literals like so:

string.split('/')[0]
// or
string.split('/')[1]
// or
string.split('/')[2]

We benefit by limiting the search space, this allows split to exit early once it attains the number of splits and to not scan the whole string:

string.split('/', 1)[0]
// and
string.split('/', 2)[1]
// and
string.split('/', 3)[2]

// Once we get to the element we want, .split exits early (faster)

Fail

string.split('/')[0]
string.split('/').at(0)

Pass

string.split('/', 1)[0]
string.split('/', 1).at(0)
string.split('/').at(-1)
string.split('/').at(numberVar)
string.split('/')[numberVar]

Proposed rule name

specify-split-limit or prefer-split-limit

Additional Info

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split#limit

Contributor guide

Tech stack
javascript
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.
1-2 days
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
Understanding of ESLint custom rulesJavaScript AST basicsFamiliarity with String.prototype.splitNode.js and npm
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
First, study the existing rules in eslint plugin unicorn (e.g., `prefer string slice`) to understand the rule structure and test patterns. Then, implement a new rule that warns when `String.prototype.split` is called without a limit argument when accessing a specific index via bracket notation or `.at()`. Write tests in `test/rules/` and add documentation. Use the provided MDN link to justify the optimization. If unsure about the rule name or scope, ask for feedback in the issue comments.