eslint-plugin-unicorn

More than 100 powerful ESLint rules

You might want to check out XO, which includes this plugin.

Install

npm install --save-dev eslint eslint-plugin-unicorn

Usage (`eslint.config.js`)

Requires ESLint >=8.23.0.

Use a preset config or configure each rule in eslint.config.js.

If you don't use the preset, ensure you use the same languageOptions config as below.

ES Module (Recommended)

import eslintPluginUnicorn from 'eslint-plugin-unicorn';
import * as eslintrc from '@eslint/eslintrc';

export default [
	{
		languageOptions: {
			globals: eslintrc.Legacy.environments.get('es2024'),
		},
		plugins: {
			unicorn: eslintPluginUnicorn,
		},
		rules: {
			'unicorn/better-regex': 'error',
			'unicorn/…': 'error',
		},
	},
	// …
];

CommonJS

'use strict';
const eslintPluginUnicorn = require('eslint-plugin-unicorn');
const eslintrc = require('@eslint/eslintrc');

module.exports = [
	{
		languageOptions: {
			globals: eslintrc.Legacy.environments.get('es2024'),
		},
		plugins: {
			unicorn: eslintPluginUnicorn,
		},
		rules: {
			'unicorn/better-regex': 'error',
			'unicorn/…': 'error',
		},
	},
	// …
];

Usage (legacy: `.eslintrc.*` or `package.json`)

Use a preset config or configure each rule in package.json.

If you don't use the preset, ensure you use the same env and parserOptions config as below.

{
	"name": "my-awesome-project",
	"eslintConfig": {
		"env": {
			"es2024": true
		},
		"parserOptions": {
			"ecmaVersion": "latest",
			"sourceType": "module"
		},
		"plugins": [
			"unicorn"
		],
		"rules": {
			"unicorn/better-regex": "error",
			"unicorn/…": "error"
		}
	}
}

Rules

💼 Configurations enabled in.
✅ Set in the recommended configuration.
🔧 Automatically fixable by the --fix CLI option.
💡 Manually fixable by editor suggestions.

Name	Description	💼	🔧	💡
better-regex	Improve regexes by making them shorter, consistent, and safer.	✅	🔧
catch-error-name	Enforce a specific parameter name in catch clauses.	✅	🔧
consistent-destructuring	Use destructured variables over properties.		🔧	💡
consistent-function-scoping	Move function definitions to the highest possible scope.	✅
custom-error-definition	Enforce correct `Error` subclassing.		🔧
empty-brace-spaces	Enforce no spaces between braces.	✅	🔧
error-message	Enforce passing a `message` value when creating a built-in error.	✅
escape-case	Require escape sequences to use uppercase values.	✅	🔧
expiring-todo-comments	Add expiration conditions to TODO comments.	✅
explicit-length-check	Enforce explicitly comparing the `length` or `size` property of a value.	✅	🔧	💡
filename-case	Enforce a case style for filenames.	✅
import-style	Enforce specific import styles per module.	✅
new-for-builtins	Enforce the use of `new` for all builtins, except `String`, `Number`, `Boolean`, `Symbol` and `BigInt`.	✅	🔧
no-abusive-eslint-disable	Enforce specifying rules to disable in `eslint-disable` comments.	✅
no-anonymous-default-export	Disallow anonymous functions and classes as the default export.	✅		💡
no-array-callback-reference	Prevent passing a function reference directly to iterator methods.	✅		💡
no-array-for-each	Prefer `for…of` over the `forEach` method.	✅	🔧	💡
no-array-method-this-argument	Disallow using the `this` argument in array methods.	✅	🔧	💡
no-array-push-push	Enforce combining multiple `Array#push()` into one call.	✅	🔧	💡
no-array-reduce	Disallow `Array#reduce()` and `Array#reduceRight()`.	✅
no-await-expression-member	Disallow member access from await expression.	✅	🔧
no-console-spaces	Do not use leading/trailing space between `console.log` parameters.	✅	🔧
no-document-cookie	Do not use `document.cookie` directly.	✅
no-empty-file	Disallow empty files.	✅
no-for-loop	Do not use a `for` loop that can be replaced with a `for-of` loop.	✅	🔧	💡
no-hex-escape	Enforce the use of Unicode escapes instead of hexadecimal escapes.	✅	🔧
no-instanceof-array	Require `Array.isArray()` instead of `instanceof Array`.	✅	🔧
no-invalid-remove-event-listener	Prevent calling `EventTarget#removeEventListener()` with the result of an expression.	✅
no-keyword-prefix	Disallow identifiers starting with `new` or `class`.
no-lonely-if	Disallow `if` statements as the only statement in `if` blocks without `else`.	✅	🔧
no-negated-condition	Disallow negated conditions.	✅	🔧
no-nested-ternary	Disallow nested ternary expressions.	✅	🔧
no-new-array	Disallow `new Array()`.	✅	🔧	💡
no-new-buffer	Enforce the use of `Buffer.from()` and `Buffer.alloc()` instead of the deprecated `new Buffer()`.	✅	🔧	💡
no-null	Disallow the use of the `null` literal.	✅	🔧	💡
no-object-as-default-parameter	Disallow the use of objects as default parameters.	✅
no-process-exit	Disallow `process.exit()`.	✅
no-static-only-class	Disallow classes that only have static members.	✅	🔧
no-thenable	Disallow `then` property.	✅
no-this-assignment	Disallow assigning `this` to a variable.	✅
no-typeof-undefined	Disallow comparing `undefined` using `typeof`.	✅	🔧	💡
no-unnecessary-await	Disallow awaiting non-promise values.	✅	🔧
no-unnecessary-polyfills	Enforce the use of built-in methods instead of unnecessary polyfills.	✅
no-unreadable-array-destructuring	Disallow unreadable array destructuring.	✅	🔧
no-unreadable-iife	Disallow unreadable IIFEs.	✅
no-unused-properties	Disallow unused object properties.
no-useless-fallback-in-spread	Disallow useless fallback when spreading in object literals.	✅	🔧
no-useless-length-check	Disallow useless array length check.	✅	🔧
no-useless-promise-resolve-reject	Disallow returning/yielding `Promise.resolve/reject()` in async functions or promise callbacks	✅	🔧
no-useless-spread	Disallow unnecessary spread.	✅	🔧
no-useless-switch-case	Disallow useless case in switch statements.	✅		💡
no-useless-undefined	Disallow useless `undefined`.	✅	🔧
no-zero-fractions	Disallow number literals with zero fractions or dangling dots.	✅	🔧
number-literal-case	Enforce proper case for numeric literals.	✅	🔧
numeric-separators-style	Enforce the style of numeric separators by correctly grouping digits.	✅	🔧
prefer-add-event-listener	Prefer `.addEventListener()` and `.removeEventListener()` over `on`-functions.	✅	🔧
prefer-array-find	Prefer `.find(…)` and `.findLast(…)` over the first or last element from `.filter(…)`.	✅	🔧	💡
prefer-array-flat	Prefer `Array#flat()` over legacy techniques to flatten arrays.	✅	🔧
prefer-array-flat-map	Prefer `.flatMap(…)` over `.map(…).flat()`.	✅	🔧
prefer-array-index-of	Prefer `Array#{indexOf,lastIndexOf}()` over `Array#{findIndex,findLastIndex}()` when looking for the index of an item.	✅	🔧	💡
prefer-array-some	Prefer `.some(…)` over `.filter(…).length` check and `.{find,findLast}(…)`.	✅	🔧	💡
prefer-at	Prefer `.at()` method for index access and `String#charAt()`.	✅	🔧	💡
prefer-blob-reading-methods	Prefer `Blob#arrayBuffer()` over `FileReader#readAsArrayBuffer(…)` and `Blob#text()` over `FileReader#readAsText(…)`.	✅
prefer-code-point	Prefer `String#codePointAt(…)` over `String#charCodeAt(…)` and `String.fromCodePoint(…)` over `String.fromCharCode(…)`.	✅		💡
prefer-date-now	Prefer `Date.now()` to get the number of milliseconds since the Unix Epoch.	✅	🔧
prefer-default-parameters	Prefer default parameters over reassignment.	✅	🔧	💡
prefer-dom-node-append	Prefer `Node#append()` over `Node#appendChild()`.	✅	🔧
prefer-dom-node-dataset	Prefer using `.dataset` on DOM elements over calling attribute methods.	✅	🔧
prefer-dom-node-remove	Prefer `childNode.remove()` over `parentNode.removeChild(childNode)`.	✅	🔧	💡
prefer-dom-node-text-content	Prefer `.textContent` over `.innerText`.	✅		💡
prefer-event-target	Prefer `EventTarget` over `EventEmitter`.	✅
prefer-export-from	Prefer `export…from` when re-exporting.	✅	🔧	💡
prefer-includes	Prefer `.includes()` over `.indexOf()` and `Array#some()` when checking for existence or non-existence.	✅	🔧	💡
prefer-json-parse-buffer	Prefer reading a JSON file as a buffer.		🔧
prefer-keyboard-event-key	Prefer `KeyboardEvent#key` over `KeyboardEvent#keyCode`.	✅	🔧
prefer-logical-operator-over-ternary	Prefer using a logical operator over a ternary.	✅		💡
prefer-math-trunc	Enforce the use of `Math.trunc` instead of bitwise operators.	✅	🔧	💡
prefer-modern-dom-apis	Prefer `.before()` over `.insertBefore()`, `.replaceWith()` over `.replaceChild()`, prefer one of `.before()`, `.after()`, `.append()` or `.prepend()` over `insertAdjacentText()` and `insertAdjacentElement()`.	✅	🔧
prefer-modern-math-apis	Prefer modern `Math` APIs over legacy patterns.	✅	🔧
prefer-module	Prefer JavaScript modules (ESM) over CommonJS.	✅	🔧	💡
prefer-native-coercion-functions	Prefer using `String`, `Number`, `BigInt`, `Boolean`, and `Symbol` directly.	✅	🔧
prefer-negative-index	Prefer negative index over `.length - index` when possible.	✅	🔧
prefer-node-protocol	Prefer using the `node:` protocol when importing Node.js builtin modules.	✅	🔧
prefer-number-properties	Prefer `Number` static properties over global ones.	✅	🔧	💡
prefer-object-from-entries	Prefer using `Object.fromEntries(…)` to transform a list of key-value pairs into an object.	✅	🔧
prefer-optional-catch-binding	Prefer omitting the `catch` binding parameter.	✅	🔧
prefer-prototype-methods	Prefer borrowing methods from the prototype instead of the instance.	✅	🔧
prefer-query-selector	Prefer `.querySelector()` over `.getElementById()`, `.querySelectorAll()` over `.getElementsByClassName()` and `.getElementsByTagName()`.	✅	🔧
prefer-reflect-apply	Prefer `Reflect.apply()` over `Function#apply()`.	✅	🔧
prefer-regexp-test	Prefer `RegExp#test()` over `String#match()` and `RegExp#exec()`.	✅	🔧	💡
prefer-set-has	Prefer `Set#has()` over `Array#includes()` when checking for existence or non-existence.	✅	🔧	💡
prefer-set-size	Prefer using `Set#size` instead of `Array#length`.	✅	🔧
prefer-spread	Prefer the spread operator over `Array.from(…)`, `Array#concat(…)`, `Array#{slice,toSpliced}()` and `String#split('')`.	✅	🔧	💡
prefer-string-replace-all	Prefer `String#replaceAll()` over regex searches with the global flag.	✅	🔧
prefer-string-slice	Prefer `String#slice()` over `String#substr()` and `String#substring()`.	✅	🔧
prefer-string-starts-ends-with	Prefer `String#startsWith()` & `String#endsWith()` over `RegExp#test()`.	✅	🔧	💡
prefer-string-trim-start-end	Prefer `String#trimStart()` / `String#trimEnd()` over `String#trimLeft()` / `String#trimRight()`.	✅	🔧
prefer-switch	Prefer `switch` over multiple `else-if`.	✅	🔧
prefer-ternary	Prefer ternary expressions over simple `if-else` statements.	✅	🔧
prefer-top-level-await	Prefer top-level await over top-level promises and async function calls.	✅		💡
prefer-type-error	Enforce throwing `TypeError` in type checking conditions.	✅	🔧
prevent-abbreviations	Prevent abbreviations.	✅	🔧
relative-url-style	Enforce consistent relative URL style.	✅	🔧	💡
require-array-join-separator	Enforce using the separator argument with `Array#join()`.	✅	🔧
require-number-to-fixed-digits-argument	Enforce using the digits argument with `Number#toFixed()`.	✅	🔧
require-post-message-target-origin	Enforce using the `targetOrigin` argument with `window.postMessage()`.			💡
string-content	Enforce better string content.		🔧	💡
switch-case-braces	Enforce consistent brace style for `case` clauses.	✅	🔧
template-indent	Fix whitespace-insensitive template indentation.	✅	🔧
text-encoding-identifier-case	Enforce consistent case for text encoding identifiers.	✅	🔧	💡
throw-new-error	Require `new` when throwing an error.	✅	🔧

Deprecated Rules

See docs/deprecated-rules.md

Preset configs (`eslint.config.js`)

See the ESLint docs for more information about extending config files.

Note: Preset configs will also enable the correct language options.

Recommended config

This plugin exports a recommended config that enforces good practices.

ES Module (Recommended)

import eslintPluginUnicorn from 'eslint-plugin-unicorn';

export default [
		// …
		eslintPluginUnicorn.configs['flat/recommended'],
		{
			rules: {
				'unicorn/better-regex': 'warn',
			},
		},
];

CommonJS

'use strict';
const eslintPluginUnicorn = require('eslint-plugin-unicorn');

module.exports = [
		// …
		eslintPluginUnicorn.configs['flat/recommended'],
		{
			rules: {
				'unicorn/better-regex': 'warn',
			},
		},
];

All config

This plugin exports an all config that makes use of all rules (except for deprecated ones).

ES Module (Recommended)

import eslintPluginUnicorn from 'eslint-plugin-unicorn';

export default [
		// …
		eslintPluginUnicorn.configs['flat/all'],
		{
			rules: {
				'unicorn/better-regex': 'warn',
			},
		},
];

CommonJS

'use strict';
const eslintPluginUnicorn = require('eslint-plugin-unicorn');

module.exports = [
		// …
		eslintPluginUnicorn.configs['flat/all'],
		{
			rules: {
				'unicorn/better-regex': 'warn',
			},
		},
];

Preset configs (`.eslintrc.*` or `package.json`)

See the ESLint docs for more information about extending config files.

Note: Preset configs will also enable the correct parser options and environment.

Recommended config

This plugin exports a recommended config that enforces good practices.

{
	"name": "my-awesome-project",
	"eslintConfig": {
		"extends": "plugin:unicorn/recommended",
		"rules": {
			"unicorn/better-regex": "warn"
		}
	}
}

All config

This plugin exports an all config that makes use of all rules (except for deprecated ones).

{
	"name": "my-awesome-project",
	"eslintConfig": {
		"extends": "plugin:unicorn/all"
	}
}