eslint-plugin-unicorn

Most rules target JavaScript and TypeScript, but some also lint CSS, HTML, JSON, Markdown, TOML, and YAML when used with the matching ESLint language plugin.

Propose a new rule ➡

We do not accept pull requests because of too much AI slop.

Install

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

Requires ESLint >=10.4, flat config, and ESM.

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

Usage

Use a preset config or configure each rule in eslint.config.js.

If you don't use a preset, set the same languageOptions as shown below.

import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';
import globals from 'globals';
export default defineConfig([
	{
		files: ['*/.js'],
		languageOptions: {
			globals: globals.builtin,
		},
		plugins: {
			unicorn,
		},
		rules: {
			'unicorn/prefer-module': 'error',
			'unicorn/…': 'error',
		},
	},
	// …
]);

For TypeScript, scope Unicorn to TypeScript files and configure a TypeScript parser for the same config object:

import typescriptEslintParser from '@typescript-eslint/parser';
import unicorn from 'eslint-plugin-unicorn';
import {defineConfig} from 'eslint/config';
import globals from 'globals';
export default defineConfig([
	{
		files: ['*/.ts'],
		languageOptions: {
			globals: globals.builtin,
			parser: typescriptEslintParser,
		},
		plugins: {
			unicorn,
		},
		rules: {
			'unicorn/prefer-module': '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.\ 💭 Requires type information.

| Name                                         | Description | 💼 | 🔧 | 💡 | 💭 | | :--------------------------------------------------------------------------------------------------------- | :----------------------------------------------------------------------------------------------------------------------------- | :--- | :- | :- | :- | | better-dom-traversing | Prefer better DOM traversal APIs. | ✅ ☑️ | | 💡 | | | catch-error-name | Enforce a specific parameter name in catch clauses. | ✅ | 🔧 | | | | class-reference-in-static-methods | Enforce consistent class references in static methods. | ✅ | | 💡 | | | comment-content | Enforce better comment content. | | 🔧 | | | | consistent-arrow-return-style | Enforce a consistent return style for multiline arrow function bodies. | | 🔧 | | | | consistent-assert | Enforce consistent assertion style with node:assert. | ✅ | 🔧 | | | | consistent-boolean-name | Enforce consistent naming for boolean names. | ✅ | 🔧 | 💡 | | | consistent-class-member-order | Enforce consistent class member order. | ✅ | | 💡 | | | consistent-compound-words | Enforce consistent spelling of compound words in identifiers. | ✅ ☑️ | | 💡 | | | consistent-conditional-object-spread | Enforce consistent conditional object spread style. | ✅ | 🔧 | | | | 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-export-decorator-position | Enforce consistent decorator position on exported classes. | ✅ ☑️ | 🔧 | | | | consistent-function-scoping | Move function definitions to the highest possible scope. | ✅ | | | | | consistent-function-style | Enforce function syntax by role. | | | 💡 | | | consistent-json-file-read | Enforce consistent JSON file reads before JSON.parse(). | ✅ | 🔧 | | | | consistent-optional-chaining | Enforce consistent optional chaining for same-base member access. | ✅ ☑️ | | 💡 | | | consistent-template-literal-escape | Enforce consistent style for escaping ${ in template literals. | ✅ | 🔧 | | | | consistent-tuple-labels | Enforce consistent labels on tuple type elements. | ✅ | | | | | custom-error-definition | Enforce correct Error subclassing. | | 🔧 | | | | default-export-style | Enforce consistent default export declarations. | ✅ | 🔧 | 💡 | | | dom-node-dataset | Enforce consistent style for DOM element dataset access. | ✅ ☑️ | 🔧 | | | | 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. | ✅ | 🔧 | 💡 | | | explicit-timer-delay | Enforce or disallow explicit delay argument for setTimeout() and setInterval(). | ✅ ☑️ | 🔧 | | | | filename-case | Enforce a case style for filenames and directory names. | ✅ | | | | | id-match | Require identifiers to match a specified regular expression. | | | | | | import-style | Enforce specific import styles per module. | ✅ ☑️ | | | | | isolated-functions | Prevent usage of variables from outside the scope of isolated functions. | ✅ | | | | | iteration-fallback-style | Enforce a consistent style for optional loop sources. | | 🔧 | | | | logical-assignment-operators | Require or disallow logical assignment operator shorthand | ✅ | 🔧 | 💡 | | | max-nested-calls | Limit the depth of nested calls. | ✅ | | | | | name-replacements | Enforce replacements for variable, property, and filenames. | ✅ | 🔧 | 💡 | | | new-for-builtins | Enforce correct use of new for builtin constructors. | ✅ ☑️ | 🔧 | 💡 | | | 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-accidental-bitwise-operator | Disallow bitwise operators where a logical operator was likely intended. | ✅ ☑️ | | 💡 | | | 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-concat-in-loop | Disallow array accumulation with Array#concat() in loops. | ✅ | | | | | no-array-fill-with-reference-type | Disallow using reference values as Array#fill() values. | ✅ ☑️ | | | | | no-array-from-fill | Disallow .fill() after Array.from({length: …}). | ✅ ☑️ | | | | | no-array-front-mutation | Disallow front-of-array mutation. | | | | | | 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-array-sort-for-min-max | Disallow sorting arrays to get the minimum or maximum value. | ✅ ☑️ | | 💡 | | | no-array-splice | Prefer Array#toSpliced() over Array#splice(). | ✅ | | 💡 | | | no-asterisk-prefix-in-documentation-comments | Disallow asterisk prefixes in documentation comments. | | 🔧 | | | | no-async-iterator-callback | Disallow asynchronous callbacks in synchronous iterator helpers. | ✅ ☑️ | | | | | no-async-promise-finally | Disallow async functions as Promise#finally() callbacks. | ✅ ☑️ | | | | | no-await-expression-member | Disallow member access from await expression. | ✅ | 🔧 | | | | no-await-in-promise-methods | Disallow using await in Promise method parameters. | ✅ ☑️ | | 💡 | | | no-barrel-files | Disallow barrel files. | | | | | | no-blob-to-file | Disallow unnecessary Blob to File conversion. | ✅ ☑️ | | 💡 | | | no-boolean-sort-comparator | Disallow boolean-returning sort comparators. | ✅ ☑️ | | 💡 | | | no-break-in-nested-loop | Disallow break and optionally continue in nested loops and switches inside loops. | ✅ | | | | | no-canvas-to-image | Prefer drawing canvases directly instead of converting them to images. | ✅ ☑️ | | | | | no-chained-comparison | Disallow chained comparisons such as a < b < c. | ✅ ☑️ | | 💡 | | | no-collection-bracket-access | Disallow accessing Map, Set, WeakMap, and WeakSet entries with bracket notation. | ✅ ☑️ | | 💡 | | | no-computed-property-existence-check | Disallow dynamic object property existence checks. | ✅ | | 💡 | | | no-confusing-array-splice | Disallow confusing uses of Array#{splice,toSpliced}(). | ✅ | | 💡 | | | no-confusing-array-with | Disallow confusing uses of Array#with(). | ✅ | | | | | no-console-spaces | Do not use leading/trailing space between console.log parameters. | ✅ ☑️ | 🔧 | | | | no-constant-zero-expression | Disallow arithmetic and bitwise operations that always evaluate to 0. | ✅ ☑️ | | 💡 | | | no-declarations-before-early-exit | Disallow declarations before conditional early exits when they are only used after the exit. | ✅ ☑️ | 🔧 | | | | no-deprecated-css-features | Disallow deprecated CSS features. | | 🔧 | 💡 | | | no-document-cookie | Do not use document.cookie directly. | ✅ ☑️ | | | | | no-double-comparison | Disallow two comparisons of the same operands that can be combined into one. | ✅ ☑️ | | 💡 | | | no-duplicate-css-selectors | Disallow duplicate CSS selectors. | | 🔧 | | | | no-duplicate-font-family-names | Disallow duplicate font family names. | | 🔧 | | | | no-duplicate-if-branches | Disallow duplicate adjacent branches in if chains. | ✅ | | | | | no-duplicate-logical-operands | Disallow adjacent duplicate operands in logical expressions. | ✅ ☑️ | 🔧 | 💡 | | | no-duplicate-loops | Disallow .map() and .filter() in for…of and for await…of loop headers. | ✅ | | | | | no-duplicate-set-values | Disallow duplicate values in Set constructor array literals. | ✅ | | | | | no-empty-file | Disallow empty files. | ✅ ☑️ | | | | | no-error-property-assignment | Disallow assigning to built-in error properties. | ✅ ☑️ | | | | | no-exports-in-scripts | Disallow exports in scripts. | ✅ ☑️ | | | | | no-for-each | Prefer for…of over the forEach method. | ✅ ☑️ | 🔧 | 💡 | | | no-for-loop | Do not use a for loop that can be replaced with a for-of loop. | ✅ | 🔧 | | | | no-global-object-property-assignment | Disallow assigning properties on the global object. | ✅ ☑️ | | | | | no-immediate-mutation | Disallow immediate mutation after variable assignment. | ✅ | 🔧 | 💡 | | | no-impossible-length-comparison | Disallow impossible comparisons against .length or .size. | ✅ ☑️ | | | | | no-incorrect-query-selector | Disallow incorrect querySelector() and querySelectorAll() usage. | ✅ | 🔧 | | | | no-incorrect-template-string-interpolation | Disallow incorrect template literal interpolation syntax. | ✅ | | 💡 | | | no-instanceof-builtins | Disallow instanceof with built-in objects | ✅ ☑️ | 🔧 | 💡 | | | no-invalid-argument-count | Disallow calling functions and constructors with an invalid number of arguments. | ✅ ☑️ | | | | | no-invalid-character-comparison | Disallow comparing a single character from a string to a multi-character string. | ✅ ☑️ | | | | | no-invalid-fetch-options | Disallow invalid options in fetch() and new Request(). | ✅ ☑️ | | | | | no-invalid-file-input-accept | Disallow invalid accept values on file inputs. | | 🔧 | | | | no-invalid-media-features | Disallow unknown media features and invalid values for known media features. | | | | | | no-invalid-remove-event-listener | Prevent calling EventTarget#removeEventListener() with the result of an expression. | ✅ ☑️ | | | | | no-invalid-well-known-symbol-methods | Disallow invalid implementations of well-known symbol methods. | ✅ ☑️ | 🔧 | 💡 | | | no-keyword-prefix | Disallow identifiers starting with new or class. | | | | | | no-late-current-target-access | Disallow accessing event.currentTarget after the synchronous event dispatch has finished. | ✅ | | | | | no-late-event-control | Disallow event-control method calls after the synchronous event dispatch has finished. | ✅ | | | | | no-lonely-if | Disallow if statements as the only statement in if blocks without else. | ✅ ☑️ | 🔧 | | | | no-loop-iterable-mutation | Disallow mutating a loop iterable during iteration. | ✅ | | | | | no-magic-array-flat-depth | Disallow a magic number as the depth argument in Array#flat(…). | ✅ ☑️ | | | | | no-manually-wrapped-comments | Disallow manually wrapped comments. | | 🔧 | | | | no-mismatched-map-key | Disallow checking a Map key before accessing a different key. | ✅ | | | | | no-misrefactored-assignment | Disallow misrefactored compound assignments where the target is duplicated in the right-hand side. | ✅ ☑️ | | 💡 | | | no-missing-local-resource | Disallow references to missing local resources. | | 🔧 | | | | no-multiple-promise-resolver-calls | Disallow calling Promise executor resolver functions more than once on the same execution path. | ✅ ☑️ | | | | | no-named-default | Disallow named usage of default import and export. | ✅ ☑️ | 🔧 | | | | no-negated-array-predicate | Disallow negated array predicate calls. | ✅ ☑️ | 🔧 | | | | no-negated-comparison | Disallow negated comparisons. | ✅ ☑️ | 🔧 | | | | 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-nesting-with-mixed-specificity | Disallow nesting under selector lists with mixed specificity. | | | | | | 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-non-function-verb-prefix | Disallow non-function values with function-style verb prefixes. | ✅ | | | 💭 | | no-nonstandard-builtin-properties | Disallow non-standard properties on built-in objects. | ✅ ☑️ | | | | | no-null | Disallow the use of the null literal. | ✅ | 🔧 | 💡 | | | no-object-as-default-parameter | Disallow the use of objects as default parameters. | ✅ ☑️ | | | | | no-object-methods-with-collections | Disallow Object methods with Map or Set. | ✅ | | 💡 | | | no-optional-chaining-on-undeclared-variable | Disallow optional chaining on undeclared variables. | ✅ | | | | | no-process-exit | Disallow process.exit(). | ✅ ☑️ | | | | | no-redundant-comparison | Disallow comparisons made redundant by an equality check in the same logical AND. | ✅ ☑️ | 🔧 | 💡 | | | no-redundant-nested-style-rules | Disallow nested style rules that do not modify the parent selector. | | 🔧 | | | | no-return-array-push | Disallow using the return value of Array#push() and Array#unshift(). | ✅ | | 💡 | | | no-selector-as-dom-name | Disallow selector syntax in DOM names. | ✅ | 🔧 | | | | no-shorthand-property-overrides | Disallow shorthand properties that override related longhand properties. | ✅ ☑️ | | | | | 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-subtraction-comparison | Prefer comparing values directly over subtracting and comparing to 0. | ✅ ☑️ | 🔧 | 💡 | | | no-thenable | Disallow then property. | ✅ ☑️ | | | | | no-this-assignment | Disallow assigning this to a variable. | ✅ ☑️ | | | | | no-this-outside-of-class | Disallow this outside of classes. | ✅ | | | | | no-top-level-assignment-in-function | Disallow assigning to top-level variables from inside functions. | ✅ | | | | | no-top-level-side-effects | Disallow top-level side effects in exported modules. | ✅ ☑️ | | | | | no-transition-all | Disallow all as a transition property. | ✅ ☑️ | | | | | no-typeof-undefined | Disallow comparing undefined using typeof. | ✅ ☑️ | 🔧 | 💡 | | | no-uncalled-method | Disallow referencing methods without calling them. | ✅ | | | | | no-undeclared-class-members | Require class members to be declared. | ✅ | | 💡 | | | no-unknown-css-annotations | Disallow unknown and noncanonical CSS annotations. | | | 💡 | | | no-unknown-pseudo-selectors | Disallow unknown pseudo-class and pseudo-element selectors. | | | | | | no-unnecessary-array-flat-depth | Disallow using 1 as the depth argument of Array#flat(). | ✅ ☑️ | 🔧 | | | | no-unnecessary-array-flat-map | Disallow Array#flatMap() callbacks that only wrap a single item. | ✅ | 🔧 | 💡 | | | 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-boolean-comparison | Disallow unnecessary comparisons against boolean literals. | ✅ | 🔧 | | | | no-unnecessary-fetch-options | Disallow unnecessary options in fetch() and new Request(). | ✅ ☑️ | 🔧 | | | | no-unnecessary-global-this | Disallow unnecessary globalThis references. | ✅ ☑️ | 🔧 | | | | no-unnecessary-nested-ternary | Disallow unnecessary nested ternary expressions. | ✅ ☑️ | 🔧 | | | | 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-unnecessary-splice | Disallow Array#splice() when simpler alternatives exist. | ✅ | 🔧 | | | | no-unnecessary-string-trim | Disallow String#trim() before String#startsWith() or String#endsWith(). | ✅ ☑️ | 🔧 | | | | no-unreadable-array-destructuring | Disallow unreadable array destructuring. | ✅ ☑️ | 🔧 | | | | no-unreadable-for-of-expression | Disallow unreadable iterable expressions in for…of and for await…of loop headers. | ✅ | | | | | no-unreadable-iife | Disallow unreadable IIFEs. | ✅ ☑️ | | 💡 | | | no-unreadable-new-expression | Disallow unreadable new expressions. | | | | | | no-unreadable-object-destructuring | Disallow unreadable object destructuring. | ✅ ☑️ | | | | | no-unsafe-buffer-conversion | Prevent unsafe use of ArrayBuffer view .buffer. | ✅ ☑️ | | 💡 | | | no-unsafe-dom-html | Disallow unsafe DOM HTML APIs. | | | | | | no-unsafe-promise-all-settled-values | Disallow reading .value from Promise.allSettled() results without a fulfilled status guard. | ✅ ☑️ | | | | | no-unsafe-property-key | Disallow unsafe values as property keys. | ✅ | | | | | no-unsafe-sqlite-interpolation | Disallow interpolation into SQL strings passed to Node’s node:sqlite APIs. | ✅ ☑️ | | | | | no-unsafe-string-replacement | Disallow non-literal replacement values in String#replace() and String#replaceAll(). | ✅ | | | | | no-unscoped-css-nesting-selector | Disallow unscoped CSS nesting selectors. | | | | | | no-unused-builtin-method-return | Disallow ignoring the return value of selected built-in methods. | ✅ ☑️ | | | | | no-unused-iterator-helper | Disallow discarding lazy iterator helpers. | ✅ ☑️ | | 💡 | | | no-unused-properties | Disallow unused object properties. | | | | | | no-useless-boolean-cast | Disallow unnecessary Boolean() casts in array predicate callbacks.

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