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eslint-plugin-unicorn Coverage Status npm version

<!-- markdownlint-disable-next-line no-inline-html --> <img src="https://cloud.githubusercontent.com/assets/170270/18659176/1cc373d0-7f33-11e6-890f-0ba35362ee7e.jpg" width="180" align="right" alt="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 >=8.56.0.

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

<!-- Do not manually modify this list. Run: `npm run fix:eslint-docs` --> <!-- begin auto-generated rules list -->

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

Name                                   Description💼🔧💡
better-regexImprove regexes by making them shorter, consistent, and safer.🔧
catch-error-nameEnforce a specific parameter name in catch clauses.✅🔧
consistent-destructuringUse destructured variables over properties.🔧💡
consistent-empty-array-spreadPrefer consistent types when spreading a ternary in an array literal.✅🔧
consistent-existence-index-checkEnforce consistent style for element existence checks with indexOf(), lastIndexOf(), findIndex(), and findLastIndex().✅🔧
consistent-function-scopingMove function definitions to the highest possible scope.✅
custom-error-definitionEnforce correct Error subclassing.🔧
empty-brace-spacesEnforce no spaces between braces.✅🔧
error-messageEnforce passing a message value when creating a built-in error.✅
escape-caseRequire escape sequences to use uppercase values.✅🔧
expiring-todo-commentsAdd expiration conditions to TODO comments.✅
explicit-length-checkEnforce explicitly comparing the length or size property of a value.✅🔧💡
filename-caseEnforce a case style for filenames.✅
import-styleEnforce specific import styles per module.✅
new-for-builtinsEnforce the use of new for all builtins, except String, Number, Boolean, Symbol and BigInt.✅🔧
no-abusive-eslint-disableEnforce specifying rules to disable in eslint-disable comments.✅
no-anonymous-default-exportDisallow anonymous functions and classes as the default export.✅💡
no-array-callback-referencePrevent passing a function reference directly to iterator methods.✅💡
no-array-for-eachPrefer for…of over the forEach method.✅🔧💡
no-array-method-this-argumentDisallow using the this argument in array methods.✅🔧💡
no-array-push-pushEnforce combining multiple Array#push() into one call.✅🔧💡
no-array-reduceDisallow Array#reduce() and Array#reduceRight().✅
no-await-expression-memberDisallow member access from await expression.✅🔧
no-await-in-promise-methodsDisallow using await in Promise method parameters.✅💡
no-console-spacesDo not use leading/trailing space between console.log parameters.✅🔧
no-document-cookieDo not use document.cookie directly.✅
no-empty-fileDisallow empty files.✅
no-for-loopDo not use a for loop that can be replaced with a for-of loop.✅🔧💡
no-hex-escapeEnforce the use of Unicode escapes instead of hexadecimal escapes.✅🔧
no-instanceof-arrayRequire Array.isArray() instead of instanceof Array.✅🔧
no-invalid-fetch-optionsDisallow invalid options in fetch() and new Request().✅
no-invalid-remove-event-listenerPrevent calling EventTarget#removeEventListener() with the result of an expression.✅
no-keyword-prefixDisallow identifiers starting with new or class.
no-length-as-slice-endDisallow using .length as the end argument of {Array,String,TypedArray}#slice().✅🔧
no-lonely-ifDisallow if statements as the only statement in if blocks without else.✅🔧
no-magic-array-flat-depthDisallow a magic number as the depth argument in Array#flat(…).✅
no-negated-conditionDisallow negated conditions.✅🔧
no-negation-in-equality-checkDisallow negated expression in equality check.✅💡
no-nested-ternaryDisallow nested ternary expressions.✅🔧
no-new-arrayDisallow new Array().✅🔧💡
no-new-bufferEnforce the use of Buffer.from() and Buffer.alloc() instead of the deprecated new Buffer().✅🔧💡
no-nullDisallow the use of the null literal.✅🔧💡
no-object-as-default-parameterDisallow the use of objects as default parameters.✅
no-process-exitDisallow process.exit().✅
no-single-promise-in-promise-methodsDisallow passing single-element arrays to Promise methods.✅🔧💡
no-static-only-classDisallow classes that only have static members.✅🔧
no-thenableDisallow then property.✅
no-this-assignmentDisallow assigning this to a variable.✅
no-typeof-undefinedDisallow comparing undefined using typeof.✅🔧💡
no-unnecessary-awaitDisallow awaiting non-promise values.✅🔧
no-unnecessary-polyfillsEnforce the use of built-in methods instead of unnecessary polyfills.✅
no-unreadable-array-destructuringDisallow unreadable array destructuring.✅🔧
no-unreadable-iifeDisallow unreadable IIFEs.✅
no-unused-propertiesDisallow unused object properties.
no-useless-fallback-in-spreadDisallow useless fallback when spreading in object literals.✅🔧
no-useless-length-checkDisallow useless array length check.✅🔧
no-useless-promise-resolve-rejectDisallow returning/yielding Promise.resolve/reject() in async functions or promise callbacks✅🔧
no-useless-spreadDisallow unnecessary spread.✅🔧
no-useless-switch-caseDisallow useless case in switch statements.✅💡
no-useless-undefinedDisallow useless undefined.✅🔧
no-zero-fractionsDisallow number literals with zero fractions or dangling dots.✅🔧
number-literal-caseEnforce proper case for numeric literals.✅🔧
numeric-separators-styleEnforce the style of numeric separators by correctly grouping digits.✅🔧
prefer-add-event-listenerPrefer .addEventListener() and .removeEventListener() over on-functions.✅🔧
prefer-array-findPrefer .find(…) and .findLast(…) over the first or last element from .filter(…).✅🔧💡
prefer-array-flatPrefer Array#flat() over legacy techniques to flatten arrays.✅🔧
prefer-array-flat-mapPrefer .flatMap(…) over .map(…).flat().✅🔧
prefer-array-index-ofPrefer Array#{indexOf,lastIndexOf}() over Array#{findIndex,findLastIndex}() when looking for the index of an item.✅🔧💡
prefer-array-somePrefer .some(…) over .filter(…).length check and .{find,findLast,findIndex,findLastIndex}(…).✅🔧💡
prefer-atPrefer .at() method for index access and String#charAt().✅🔧💡
prefer-blob-reading-methodsPrefer Blob#arrayBuffer() over FileReader#readAsArrayBuffer(…) and Blob#text() over FileReader#readAsText(…).✅
prefer-code-pointPrefer String#codePointAt(…) over String#charCodeAt(…) and String.fromCodePoint(…) over String.fromCharCode(…).✅💡
prefer-date-nowPrefer Date.now() to get the number of milliseconds since the Unix Epoch.✅🔧
prefer-default-parametersPrefer default parameters over reassignment.✅🔧💡
prefer-dom-node-appendPrefer Node#append() over Node#appendChild().✅🔧
prefer-dom-node-datasetPrefer using .dataset on DOM elements over calling attribute methods.✅🔧
prefer-dom-node-removePrefer childNode.remove() over parentNode.removeChild(childNode).✅🔧💡
prefer-dom-node-text-contentPrefer .textContent over .innerText.✅💡
prefer-event-targetPrefer EventTarget over EventEmitter.✅
prefer-export-fromPrefer export…from when re-exporting.✅🔧💡
prefer-global-thisPrefer globalThis over window, self, and global.✅🔧
prefer-includesPrefer .includes() over .indexOf(), .lastIndexOf(), and Array#some() when checking for existence or non-existence.✅🔧💡
prefer-json-parse-bufferPrefer reading a JSON file as a buffer.🔧
prefer-keyboard-event-keyPrefer KeyboardEvent#key over KeyboardEvent#keyCode.✅🔧
prefer-logical-operator-over-ternaryPrefer using a logical operator over a ternary.✅💡
prefer-math-min-maxPrefer Math.min() and Math.max() over ternaries for simple comparisons.✅🔧
prefer-math-truncEnforce the use of Math.trunc instead of bitwise operators.✅🔧💡
prefer-modern-dom-apisPrefer .before() over .insertBefore(), .replaceWith() over .replaceChild(), prefer one of .before(), .after(), .append() or .prepend() over insertAdjacentText() and insertAdjacentElement().✅🔧
prefer-modern-math-apisPrefer modern Math APIs over legacy patterns.✅🔧
prefer-modulePrefer JavaScript modules (ESM) over CommonJS.✅🔧💡
prefer-native-coercion-functionsPrefer using String, Number, BigInt, Boolean, and Symbol directly.✅🔧
prefer-negative-indexPrefer negative index over .length - index when possible.✅🔧
prefer-node-protocolPrefer using the node: protocol when importing Node.js builtin modules.✅🔧
prefer-number-propertiesPrefer Number static properties over global ones.✅🔧💡
prefer-object-from-entriesPrefer using Object.fromEntries(…) to transform a list of key-value pairs into an object.✅🔧
prefer-optional-catch-bindingPrefer omitting the catch binding parameter.✅🔧
prefer-prototype-methodsPrefer borrowing methods from the prototype instead of the instance.✅🔧
prefer-query-selectorPrefer .querySelector() over .getElementById(), .querySelectorAll() over .getElementsByClassName() and .getElementsByTagName() and .getElementsByName().✅🔧
prefer-reflect-applyPrefer Reflect.apply() over Function#apply().✅🔧
prefer-regexp-testPrefer RegExp#test() over String#match() and RegExp#exec().✅🔧💡
prefer-set-hasPrefer Set#has() over Array#includes() when checking for existence or non-existence.✅🔧💡
prefer-set-sizePrefer using Set#size instead of Array#length.✅🔧
prefer-spreadPrefer the spread operator over Array.from(…), Array#concat(…), Array#{slice,toSpliced}() and String#split('').✅🔧💡
prefer-string-rawPrefer using the String.raw tag to avoid escaping \.✅🔧
prefer-string-replace-allPrefer String#replaceAll() over regex searches with the global flag.✅🔧
prefer-string-slicePrefer String#slice() over String#substr() and String#substring().✅🔧
prefer-string-starts-ends-withPrefer String#startsWith() & String#endsWith() over RegExp#test().✅🔧💡
prefer-string-trim-start-endPrefer String#trimStart() / String#trimEnd() over String#trimLeft() / String#trimRight().✅🔧
prefer-structured-clonePrefer using structuredClone to create a deep clone.✅💡
prefer-switchPrefer switch over multiple else-if.✅🔧
prefer-ternaryPrefer ternary expressions over simple if-else statements.✅🔧
prefer-top-level-awaitPrefer top-level await over top-level promises and async function calls.✅💡
prefer-type-errorEnforce throwing TypeError in type checking conditions.✅🔧
prevent-abbreviationsPrevent abbreviations.✅🔧
relative-url-styleEnforce consistent relative URL style.✅🔧💡
require-array-join-separatorEnforce using the separator argument with Array#join().✅🔧
require-number-to-fixed-digits-argumentEnforce using the digits argument with Number#toFixed().✅🔧
require-post-message-target-originEnforce using the targetOrigin argument with window.postMessage().💡
string-contentEnforce better string content.🔧💡
switch-case-bracesEnforce consistent brace style for case clauses.✅🔧
template-indentFix whitespace-insensitive template indentation.✅🔧
text-encoding-identifier-caseEnforce consistent case for text encoding identifiers.✅🔧💡
throw-new-errorRequire new when creating an error.✅🔧
<!-- end auto-generated rules list -->

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