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eslint-plugin-unicorn Coverage Status npm version

Unicorn

More than 100 powerful ESLint rules

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

Propose or contribute a new rule ➑

Install

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

Usage (eslint.config.js)

Requires ESLint >=8.56.0.

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 globals from 'globals';

export default [
	{
		languageOptions: {
			globals: globals.builtin,
		},
		plugins: {
			unicorn: eslintPluginUnicorn,
		},
		rules: {
			'unicorn/better-regex': 'error',
			'unicorn/…': 'error',
		},
	},
	// …
];

CommonJS

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

module.exports = [
	{
		languageOptions: {
			globals: globals.builtin,
		},
		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

πŸ’Ό Configurations enabled in.
βœ… Set in the recommended configuration.
πŸ”§ Automatically fixable by the --fix CLI option.
πŸ’‘ Manually fixable by editor suggestions.

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

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"
	}
}

Maintainers

Former