@lint-suite/eslint-arrow-fits-line

This ESLint plugin keeps TypeScript and JavaScript expression-bodied arrow functions readable by requiring the expression body itself to occupy one physical source line. It reports multi-line non-object expression bodies and fixes them by adding a block with an explicit return; it does not impose a maximum line width.

Install

Requires Node.js 24, ESLint ^10.9.1, and TypeScript >=6.0.3 (required by typescript-eslint's runtime utilities).

pnpm add -D @lint-suite/eslint-arrow-fits-line eslint typescript

// eslint.config.js
import arrowBody from '@lint-suite/eslint-arrow-fits-line';

export default [
  {
    plugins: { arrowBody },
    rules: { 'arrowBody/arrow-fits-line': 'error' }
  }
];

For TypeScript syntax, configure a TypeScript parser such as typescript-eslint separately. This rule does not require type services. Installing this plugin does not configure a parser.

Behavior

There are no options. Severity is chosen by the consumer. The rule checks the physical lines occupied by an expression body, not its rendered width: do not reformat these examples across lines if you want the same result. Parentheses around a reported body are removed by the fix. Object-expression bodies and existing block bodies are exempt.

Examples

Each example is checked by this rule alone, not by an entire ESLint suite.

Valid examples

1. Single-line property read

const idOf = (user) => user.id;

2. Single-line logical expression

const isReady = (value) => value.loaded && value.enabled;

3. Multi-line parameters with a one-line body

const sum = (
  left,
  right
) => left + right;

4. Multi-line object expression

const createUser = () => ({
  active: true
});

5. Block-bodied arrow function

const load = async () => {
  return fetch('/api/user');
};

Invalid examples

1. Logical expression split after an operator

const isAllowed = (user) => user.active &&
  user.verified;

2. Parenthesized expression body on several lines

const isComplete = () => (
  loaded &&
  saved
);

3. Multi-line conditional expression

const label = (ready) => ready
  ? 'Ready'
  : 'Waiting';

4. Multi-line member-call expression

const first = () => items
  .find((item) => item.active);

5. Multi-line call arguments in the body

const message = () => format(
  title,
  count
);

The default export is an ESLint plugin; the named arrowFitsLineRule export is intended for composed rule registries. Versions are released independently from other @lint-suite packages.