sindresorhus/eslint-plugin-unicorn

Rule proposal: Enforce compare function style for `Array#sort()`

Open

#1,473 opened on Aug 8, 2021

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

Description

I've seen many people just write the compare function too complicated, yes sometimes maybe it's more readable, but sometimes it's just too long.

Fail

array.sort((a, b) => {
	if (a > b) {
		return 1;
	}

	if (a < b) {
		return -1;
	}

	return 0;
});

array.sort((a, b) => a > b ? 1 : -1);

array.sort((a, b) => {
	if (a.foo > b.foo) {
		return 1;
	}

	if (a.foo < b.foo) {
		return -1;
	}

	if (a.bar > b.bar) {
		return 1;
	}

	if (a.bar < b.bar) {
		return -1;
	}

	return 0;
});

array.sort(() => Math.random() > 0. 5 ? 1 : -1);

Pass

array.sort((a, b) => a - b);

array.sort((a, b) => a.localeCompare(b));

array.sort((a, b) => a.foo - b.foo || a.bar - b.bar);

array.sort(() => Math.random() - 0.5);

This rule should not fixable unless we are sure they are numbers.

Contributor guide

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.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaScriptESLint rule creation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Review existing rules in the repository (e.g., src/rules/) to understand the pattern for creating a new ESLint rule. The rule should inspect the callback passed to Array.prototype.sort() and detect if it uses a verbose if else pattern instead of a concise subtraction or localeCompare. Use AST node types like ArrowFunctionExpression or FunctionExpression and examine the function body for return statements with conditionals. Refer to ESLint's documentation on custom rules and the plugin's existing test structure.