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

Various awesome 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

Configure it in package.json.

{
	"name": "my-awesome-project",
	"eslintConfig": {
		"env": {
			"es6": true
		},
		"parserOptions": {
			"ecmaVersion": 2021,
			"sourceType": "module"
		},
		"plugins": [
			"unicorn"
		],
		"rules": {
			"unicorn/better-regex": "error",
			"unicorn/catch-error-name": "error",
			"unicorn/consistent-destructuring": "error",
			"unicorn/consistent-function-scoping": "error",
			"unicorn/custom-error-definition": "off",
			"unicorn/empty-brace-spaces": "error",
			"unicorn/error-message": "error",
			"unicorn/escape-case": "error",
			"unicorn/expiring-todo-comments": "error",
			"unicorn/explicit-length-check": "error",
			"unicorn/filename-case": "error",
			"unicorn/import-index": "off",
			"unicorn/import-style": "error",
			"unicorn/new-for-builtins": "error",
			"unicorn/no-abusive-eslint-disable": "error",
			"unicorn/no-array-callback-reference": "error",
			"unicorn/no-array-for-each": "error",
			"unicorn/no-array-method-this-argument": "error",
			"unicorn/no-array-push-push": "error",
			"unicorn/no-array-reduce": "error",
			"unicorn/no-console-spaces": "error",
			"unicorn/no-document-cookie": "error",
			"unicorn/no-for-loop": "error",
			"unicorn/no-hex-escape": "error",
			"unicorn/no-instanceof-array": "error",
			"unicorn/no-keyword-prefix": "off",
			"unicorn/no-lonely-if": "error",
			"no-nested-ternary": "off",
			"unicorn/no-nested-ternary": "error",
			"unicorn/no-new-array": "error",
			"unicorn/no-new-buffer": "error",
			"unicorn/no-null": "error",
			"unicorn/no-object-as-default-parameter": "error",
			"unicorn/no-process-exit": "error",
			"unicorn/no-static-only-class": "error",
			"unicorn/no-this-assignment": "error",
			"unicorn/no-unreadable-array-destructuring": "error",
			"unicorn/no-unsafe-regex": "off",
			"unicorn/no-unused-properties": "off",
			"unicorn/no-useless-length-check": "error",
			"unicorn/no-useless-spread": "error",
			"unicorn/no-useless-undefined": "error",
			"unicorn/no-zero-fractions": "error",
			"unicorn/number-literal-case": "error",
			"unicorn/numeric-separators-style": "error",
			"unicorn/prefer-add-event-listener": "error",
			"unicorn/prefer-array-find": "error",
			"unicorn/prefer-array-flat": "error",
			"unicorn/prefer-array-flat-map": "error",
			"unicorn/prefer-array-index-of": "error",
			"unicorn/prefer-array-some": "error",
			"unicorn/prefer-at": "off",
			"unicorn/prefer-date-now": "error",
			"unicorn/prefer-default-parameters": "error",
			"unicorn/prefer-dom-node-append": "error",
			"unicorn/prefer-dom-node-dataset": "error",
			"unicorn/prefer-dom-node-remove": "error",
			"unicorn/prefer-dom-node-text-content": "error",
			"unicorn/prefer-includes": "error",
			"unicorn/prefer-keyboard-event-key": "error",
			"unicorn/prefer-math-trunc": "error",
			"unicorn/prefer-modern-dom-apis": "error",
			"unicorn/prefer-module": "error",
			"unicorn/prefer-negative-index": "error",
			"unicorn/prefer-node-protocol": "error",
			"unicorn/prefer-number-properties": "error",
			"unicorn/prefer-object-from-entries": "error",
			"unicorn/prefer-object-has-own": "off",
			"unicorn/prefer-optional-catch-binding": "error",
			"unicorn/prefer-prototype-methods": "error",
			"unicorn/prefer-query-selector": "error",
			"unicorn/prefer-reflect-apply": "error",
			"unicorn/prefer-regexp-test": "error",
			"unicorn/prefer-set-has": "error",
			"unicorn/prefer-spread": "error",
			"unicorn/prefer-string-replace-all": "off",
			"unicorn/prefer-string-slice": "error",
			"unicorn/prefer-string-starts-ends-with": "error",
			"unicorn/prefer-string-trim-start-end": "error",
			"unicorn/prefer-switch": "error",
			"unicorn/prefer-ternary": "error",
			"unicorn/prefer-top-level-await": "off",
			"unicorn/prefer-type-error": "error",
			"unicorn/prevent-abbreviations": "error",
			"unicorn/require-array-join-separator": "error",
			"unicorn/require-number-to-fixed-digits-argument": "error",
			"unicorn/require-post-message-target-origin": "error",
			"unicorn/string-content": "off",
			"unicorn/throw-new-error": "error"
		},
		"overrides": [
			{
				"files": [
					"*.ts",
					"*.tsx"
				],
				"rules": {
					"unicorn/require-post-message-target-origin": "off"
				}
			}
		]
	}
}

Rules

Each rule has emojis denoting:

• ✅ if it belongs to the recommended configuration
• 🔧 if some problems reported by the rule are automatically fixable by the --fix command line option
• 💡 if some problems reported by the rule are 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-index	Enforce importing index files with ..		🔧
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 Array#forEach(…).	✅	🔧
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-console-spaces	Do not use leading/trailing space between console.log parameters.	✅	🔧
no-document-cookie	Do not use document.cookie directly.	✅
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-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-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	Forbid classes that only have static members.	✅	🔧
no-this-assignment	Disallow assigning this to a variable.	✅
no-unreadable-array-destructuring	Disallow unreadable array destructuring.	✅	🔧
no-unsafe-regex	Disallow unsafe regular expressions.
no-unused-properties	Disallow unused object properties.
no-useless-length-check	Disallow useless array length check.	✅	🔧
no-useless-spread	Disallow unnecessary spread.	✅	🔧
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(…) over the first 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() over Array#findIndex() when looking for the index of an item.	✅	🔧	💡
prefer-array-some	Prefer .some(…) over .filter(…).length check and .find(…).	✅	🔧	💡
prefer-at	Prefer .at() method for index access and String#charAt().		🔧	💡
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 .setAttribute(…).	✅	🔧
prefer-dom-node-remove	Prefer childNode.remove() over parentNode.removeChild(childNode).	✅	🔧	💡
prefer-dom-node-text-content	Prefer .textContent over .innerText.	✅		💡
prefer-includes	Prefer .includes() over .indexOf() and Array#some() when checking for existence or non-existence.	✅	🔧	💡
prefer-keyboard-event-key	Prefer KeyboardEvent#key over KeyboardEvent#keyCode.	✅	🔧
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-module	Prefer JavaScript modules (ESM) over CommonJS.	✅	🔧	💡
prefer-negative-index	Prefer negative index over .length - index for {String,Array,TypedArray}#slice(), Array#splice() and Array#at().	✅	🔧
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-object-has-own	Prefer Object.hasOwn(…) over Object.prototype.hasOwnProperty.call(…).		🔧
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-spread	Prefer the spread operator over Array.from(…), Array#concat(…) and Array#slice().	✅	🔧	💡
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.	✅	🔧
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.		🔧	💡
throw-new-error	Require new when throwing an error.	✅	🔧

Deprecated Rules

See docs/deprecated-rules.md

Recommended config

This plugin exports a recommended config that enforces good practices.

Enable it in your package.json with the extends option:

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

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

Note: This config will also enable the correct parser options and environment.

Maintainers

• Sindre Sorhus
• Adam Babcock
• futpib
• Fisker Cheung

Former

• Jeroen Engels
• Sam Verschueren