#arrow-parens

#Configuration

import { defineConfig, stylisticPlugin } from '@rslint/core';

export default defineConfig([
  stylisticPlugin.configs.recommended,
  {
    rules: {
      '@stylistic/arrow-parens': 'error',
    },
  },
]);

Require parentheses around arrow function arguments.

#Rule Details

This rule enforces parentheses around the parameter of arrow functions that take a single argument. Multi-parameter and zero-parameter arrows are never reported — JavaScript syntactically requires parentheses around them, so the rule has no decision to make.

The default option is "always", which requires parentheses around every single-parameter arrow.

#Options

This rule has a string option:

• "always" (default) requires parentheses around every single-parameter arrow.
• "as-needed" removes parentheses when the parameter is a plain identifier with no annotation, default, optional marker, rest, or comments.

This rule has an object option, only meaningful with "as-needed":

• "requireForBlockBody": true reverses the requirement when the arrow's body is a block — a => { ... } becomes invalid, (a) => { ... } becomes correct.

#always

Examples of incorrect code for this rule with the default "always" option:

a => {};
a => a;
a.then(foo => {});

Examples of correct code for this rule with the default "always" option:

() => {};
(a) => {};
(a) => a;
a.then((foo) => {});

#as-needed

Examples of incorrect code for this rule with the "as-needed" option:

{ "@stylistic/arrow-parens": ["error", "as-needed"] }

(a) => a;

Examples of correct code for this rule with the "as-needed" option:

{ "@stylistic/arrow-parens": ["error", "as-needed"] }

() => {};
a => {};
a => a;
([a, b]) => a;
({ a, b }) => a;
(a = 10) => a;
(...a) => a[0];
(a, b) => a + b;

The exceptions that keep parentheses under "as-needed":

• Destructured parameters (([a]) => a, ({a}) => a).
• A parameter with a default value ((a = 1) => a).
• A rest parameter ((...a) => a).
• A TypeScript optional parameter ((a?: number) => a).
• A parameter with a type annotation ((a: number) => a).
• An arrow with a return type annotation ((a): number => a).
• An arrow with generic type parameters (<T>(a) => a).
• A comment between the parentheses ((/* doc */ a) => a).

#requireForBlockBody

Examples of incorrect code for this rule with "as-needed", { "requireForBlockBody": true }:

{ "@stylistic/arrow-parens": ["error", "as-needed", { "requireForBlockBody": true }] }

(a) => a;
a => { return a; };

Examples of correct code for this rule with "as-needed", { "requireForBlockBody": true }:

{ "@stylistic/arrow-parens": ["error", "as-needed", { "requireForBlockBody": true }] }

a => a;
(a) => { return a; };
a => ({});

#Original Documentation

• @stylistic/arrow-parens