eslint-plugin-prefer-arrow-functions

An ESLint Plugin to Lint and auto-fix plain Functions into Arrow Functions, in all cases where conversion would result in the same behaviour (Arrow Functions do not support this, arguments, or new.target for example).

Installation

npm install --save-dev eslint eslint-plugin-prefer-arrow-functions

Configuration

Flat

For ESLint 9 and above.

eslint.config.mjs:

import pluginJs from '@eslint/js';
import preferArrowFunctions from 'eslint-plugin-prefer-arrow-functions';

export default [
  pluginJs.configs.all,
  {
    plugins: {
      'prefer-arrow-functions': preferArrowFunctions
    },
    rules: {
      'prefer-arrow-functions/prefer-arrow-functions': [
        'warn',
        {
          allowedNames: [],
          allowNamedFunctions: false,
          allowObjectProperties: false,
          classPropertiesAllowed: false,
          disallowPrototype: false,
          returnStyle: 'unchanged',
          singleReturnOnly: false,
        },
      ],
    },
  },
];

Legacy

For ESLint 8 and below.

Add the plugin to the plugins section and the rule to the rules section in your .eslintrc. The default values for options are listed in this example.

{
  "plugins": ["prefer-arrow-functions"],
  "rules": {
    "prefer-arrow-functions/prefer-arrow-functions": [
      "warn",
      {
        "allowedNames": [],
        "allowNamedFunctions": false,
        "allowObjectProperties": false,
        "classPropertiesAllowed": false,
        "disallowPrototype": false,
        "returnStyle": "unchanged",
        "singleReturnOnly": false
      }
    ]
  }
}

Options

allowedNames

An optional array of function names to ignore. When set, the rule won't report named functions such as function foo() {} whose name is identical to a member of this array.

allowNamedFunctions

Controls how named functions are handled:

• When true, the rule won't report any named functions such as function foo() {}. Anonymous functions such as const foo = function() {} will still be reported.
• When "only-expressions", the rule will allow named function expressions (like callback(function namedFn() {})) but will still transform named function declarations (like function foo() {}).
• When false (default), all functions will be transformed to arrow functions when safe to do so.

allowObjectProperties

If set to true, the rule won't report named methods such as

const myObj = {
  hello() {},
};

classPropertiesAllowed

When true, functions defined as class instance fields will be converted to arrow functions when doing so would not alter or break their behaviour.

disallowPrototype

When true, functions assigned to a prototype will be converted to arrow functions when doing so would not alter or break their behaviour.

returnStyle

• When "implicit", arrow functions such as x => { return x; } will be converted to x => x.
• When "explicit", arrow functions such as x => x will be converted to x => { return x; }.
• When "unchanged" or not set, arrow functions will be left as they were.

singleReturnOnly

When true, only function declarations which only contain a return statement will be converted. Functions containing block statements will be ignored.

This option works well in conjunction with ESLint's built-in arrow-body-style set to as-needed.

Credits

This project is a fork of https://github.com/TristonJ/eslint-plugin-prefer-arrow by Triston Jones.

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