eslint-plugin-unicorn

What is eslint-plugin-unicorn?

The eslint-plugin-unicorn package is a set of ESLint rules that aim to improve code quality by enforcing best practices, preventing common mistakes, and suggesting modern syntax and methods. It includes a variety of rules that are not covered by the core ESLint rules or other plugins, focusing on code enhancements and consistency.

What are eslint-plugin-unicorn's main functionalities?

Filename Case

Enforces a specific case for filenames, which can be configured to be kebab-case, camelCase, or snake_case. This helps maintain consistency in the naming of files across a project.

"unicorn/filename-case": ["error", {"case": "kebabCase"}]

Number Literal Case

Enforces lowercase identifier and uppercase value for number literals, improving readability and consistency in the code.

"unicorn/number-literal-case": "error"

Prevent Abbreviations

Discourages the use of abbreviations in variable names, function names, and other identifiers to improve code clarity and readability.

"unicorn/prevent-abbreviations": ["error", {"replacements": {"temp": false, "err": {"error": true}}}]

Better Regex

Suggests simpler and more optimized regular expressions to improve performance and readability.

"unicorn/better-regex": "error"

Consistent Function Scoping

Enforces that functions are defined at the highest possible level, which can help with readability and reduce the complexity of nested functions.

"unicorn/consistent-function-scoping": "error"

Other packages similar to eslint-plugin-unicorn

eslint-plugin-import

This plugin provides linting rules related to ES2015+ import/export syntax, helping to ensure proper import order, naming, and file path correctness. It is similar to eslint-plugin-unicorn in that it enforces best practices, but it focuses specifically on module import and export issues.

eslint-plugin-promise

This plugin enforces best practices for JavaScript promises. It is similar to eslint-plugin-unicorn in its goal to improve code quality, but it focuses specifically on the use of promises and asynchronous code.

eslint-plugin-jsx-a11y

This plugin checks JSX code for accessibility issues, ensuring that web applications are accessible to users with disabilities. While eslint-plugin-unicorn focuses on general JavaScript code quality, eslint-plugin-jsx-a11y focuses on accessibility concerns in React and JSX.

eslint-plugin-react

This plugin provides React-specific linting rules. It is similar to eslint-plugin-unicorn in that it helps maintain code quality and consistency, but it is tailored specifically for React development.

README

eslint-plugin-unicorn

More than 100 powerful ESLint rules

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

Propose or contribute a new rule ➡

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-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"
	}
}

Maintainers

• Sindre Sorhus
• Fisker Cheung
• Bryan Mishkin
• futpib

Former

• Jeroen Engels
• Sam Verschueren
• Adam Babcock