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

Requires ESLint >=9.20.0, flat config, and ESM.

Usage

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.

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',
		},
	},
	// …
];

Rules

💼 Configurations enabled in.
✅ Set in the recommended configuration.
☑️ Set in the unopinionated 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-assert	Enforce consistent assertion style with node:assert.	✅	🔧
consistent-date-clone	Prefer passing Date directly to the constructor when cloning.	✅ ☑️	🔧
consistent-destructuring	Use destructured variables over properties.			💡
consistent-empty-array-spread	Prefer consistent types when spreading a ternary in an array literal.	✅	🔧
consistent-existence-index-check	Enforce consistent style for element existence checks with indexOf(), lastIndexOf(), findIndex(), and findLastIndex().	✅ ☑️	🔧
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 or lowercase 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-accessor-recursion	Disallow recursive access to this within getters and setters.	✅ ☑️
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-reduce	Disallow Array#reduce() and Array#reduceRight().	✅
no-array-reverse	Prefer Array#toReversed() over Array#reverse().	✅ ☑️		💡
no-array-sort	Prefer Array#toSorted() over Array#sort().	✅ ☑️		💡
no-await-expression-member	Disallow member access from await expression.	✅	🔧
no-await-in-promise-methods	Disallow using await in Promise method parameters.	✅ ☑️		💡
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-builtins	Disallow instanceof with built-in objects	✅ ☑️	🔧	💡
no-invalid-fetch-options	Disallow invalid options in fetch() and new Request().	✅ ☑️
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-magic-array-flat-depth	Disallow a magic number as the depth argument in Array#flat(…).	✅ ☑️
no-named-default	Disallow named usage of default import and export.	✅ ☑️	🔧
no-negated-condition	Disallow negated conditions.	✅ ☑️	🔧
no-negation-in-equality-check	Disallow negated expression in equality check.	✅ ☑️		💡
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-single-promise-in-promise-methods	Disallow passing single-element arrays to Promise methods.	✅ ☑️	🔧	💡
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-array-flat-depth	Disallow using 1 as the depth argument of Array#flat().	✅ ☑️	🔧
no-unnecessary-array-splice-count	Disallow using .length or Infinity as the deleteCount or skipCount argument of Array#{splice,toSpliced}().	✅ ☑️	🔧
no-unnecessary-await	Disallow awaiting non-promise values.	✅ ☑️	🔧
no-unnecessary-polyfills	Enforce the use of built-in methods instead of unnecessary polyfills.	✅ ☑️
no-unnecessary-slice-end	Disallow using .length or Infinity as the end argument of {Array,String,TypedArray}#slice().	✅ ☑️	🔧
no-unreadable-array-destructuring	Disallow unreadable array destructuring.	✅ ☑️	🔧
no-unreadable-iife	Disallow unreadable IIFEs.	✅ ☑️
no-unused-properties	Disallow unused object properties.
no-useless-error-capture-stack-trace	Disallow unnecessary Error.captureStackTrace(…).	✅ ☑️	🔧
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,findIndex,findLastIndex}(…).	✅ ☑️	🔧	💡
prefer-at	Prefer .at() method for index access and String#charAt().	✅ ☑️	🔧	💡
prefer-bigint-literals	Prefer BigInt literals over the constructor.	✅ ☑️	🔧	💡
prefer-blob-reading-methods	Prefer Blob#arrayBuffer() over FileReader#readAsArrayBuffer(…) and Blob#text() over FileReader#readAsText(…).	✅ ☑️
prefer-class-fields	Prefer class field declarations over this assignments in constructors.	✅ ☑️	🔧	💡
prefer-classlist-toggle	Prefer using Element#classList.toggle() to toggle class names.	✅ ☑️	🔧	💡
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-global-this	Prefer globalThis over window, self, and global.	✅ ☑️	🔧
prefer-import-meta-properties	Prefer import.meta.{dirname,filename} over legacy techniques for getting file paths.		🔧
prefer-includes	Prefer .includes() over .indexOf(), .lastIndexOf(), 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-min-max	Prefer Math.min() and Math.max() over ternaries for simple comparisons.	✅ ☑️	🔧
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() and .getElementsByName().	✅	🔧
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-single-call	Enforce combining multiple Array#push(), Element#classList.{add,remove}(), and importScripts() into one call.	✅ ☑️	🔧	💡
prefer-spread	Prefer the spread operator over Array.from(…), Array#concat(…), Array#{slice,toSpliced}() and String#split('').	✅	🔧	💡
prefer-string-raw	Prefer using the String.raw tag to avoid escaping \.	✅ ☑️	🔧
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-structured-clone	Prefer using structuredClone to create a deep clone.	✅ ☑️		💡
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-module-attributes	Require non-empty module attributes for imports and exports	✅ ☑️	🔧
require-module-specifiers	Require non-empty specifier list in import and export statements.	✅ ☑️	🔧	💡
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 creating an error.	✅ ☑️	🔧

Deleted and deprecated rules

See the list.

Preset configs

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.

import eslintPluginUnicorn from 'eslint-plugin-unicorn';

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

All config

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

import eslintPluginUnicorn from 'eslint-plugin-unicorn';

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

Maintainers

• Sindre Sorhus
• Fisker Cheung
• Bryan Mishkin
• futpib

Former

• Jeroen Engels
• Sam Verschueren
• Adam Babcock