Rules overview

This page lists all rules provided by eslint-plugin-unicorn. Rules are grouped by category: Best Practices, Prefer Modern APIs, and Code Style & Consistency.

Legend

Symbol	Meaning
✅	Set in the `recommended` configuration
☑️	Set in the `unopinionated` configuration
🔧	Automatically fixable by the `--fix` CLI option
💡	Manually fixable by editor suggestions

The recommended config enables a curated subset of rules marked ✅. The all config enables every rule in the plugin, including those not in any preset. Rules marked ☑️ (without ✅) appear only in the unopinionated config. See preset configs for details.

Best Practices

Rules that prevent bugs, enforce sound coding patterns, and improve correctness.

Rule	Description	Config	Fix	Suggestion
`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.	✅
`consistent-template-literal-escape`	Enforce consistent style for escaping `${` in template literals.	✅	🔧
`custom-error-definition`	Enforce correct `Error` subclassing.		🔧
`error-message`	Enforce passing a `message` value when creating a built-in error.	✅ ☑️
`expiring-todo-comments`	Add expiration conditions to TODO comments.	✅ ☑️
`isolated-functions`	Prevent usage of variables from outside the scope of isolated functions.	✅
`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-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-immediate-mutation`	Disallow immediate mutation after variable assignment.	✅	🔧	💡
`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-magic-array-flat-depth`	Disallow a magic number as the `depth` argument in `Array#flat(…)`.	✅ ☑️
`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-collection-argument`	Disallow useless values or fallbacks in `Set`, `Map`, `WeakSet`, or `WeakMap`.	✅ ☑️	🔧	💡
`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-iterator-to-array`	Disallow unnecessary `.toArray()` on iterators.	✅ ☑️	🔧	💡
`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.	✅ ☑️	🔧
`prefer-type-error`	Enforce throwing `TypeError` in type checking conditions.	✅ ☑️	🔧
`prevent-abbreviations`	Prevent abbreviations.	✅	🔧
`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 creating an error.	✅ ☑️	🔧

Prefer Modern APIs

Rules that encourage modern JavaScript and Node.js APIs over legacy equivalents.

Rule	Description	Config	Fix	Suggestion
`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-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()`, and modern insertion methods 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()`, `.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-response-static-json`	Prefer `Response.json()` over `new Response(JSON.stringify())`.	✅ ☑️	🔧
`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-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-top-level-await`	Prefer top-level await over top-level promises and async function calls.	✅ ☑️		💡

Code Style & Consistency

Rules that enforce consistent formatting, naming conventions, and structural patterns.

Rule	Description	Config	Fix	Suggestion
`empty-brace-spaces`	Enforce no spaces between braces.	✅	🔧
`escape-case`	Require escape sequences to use uppercase or lowercase values.	✅ ☑️	🔧
`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.	✅ ☑️
`no-console-spaces`	Do not use leading/trailing space between `console.log` parameters.	✅ ☑️	🔧
`no-hex-escape`	Enforce the use of Unicode escapes instead of hexadecimal escapes.	✅ ☑️	🔧
`no-lonely-if`	Disallow `if` statements as the only statement in `if` blocks without `else`.	✅ ☑️	🔧
`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.	✅	🔧	💡
`number-literal-case`	Enforce proper case for numeric literals.	✅ ☑️	🔧
`numeric-separators-style`	Enforce the style of numeric separators by correctly grouping digits.	✅ ☑️	🔧
`prefer-logical-operator-over-ternary`	Prefer using a logical operator over a ternary.	✅ ☑️		💡
`prefer-simple-condition-first`	Prefer simple conditions first in logical expressions.	✅ ☑️	🔧	💡
`prefer-single-call`	Enforce combining multiple `Array#push()`, `Element#classList.{add,remove}()`, and `importScripts()` into one call.	✅ ☑️	🔧	💡
`prefer-switch`	Prefer `switch` over multiple `else-if`.	✅ ☑️	🔧
`prefer-ternary`	Prefer ternary expressions over simple `if-else` statements.	✅ ☑️	🔧
`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()`.	✅ ☑️	🔧
`switch-case-braces`	Enforce consistent brace style for `case` clauses.	✅	🔧
`switch-case-break-position`	Enforce consistent `break`/`return`/`continue`/`throw` position in `case` clauses.	✅	🔧
`template-indent`	Fix whitespace-insensitive template indentation.	✅	🔧
`text-encoding-identifier-case`	Enforce consistent case for text encoding identifiers.	✅ ☑️	🔧	💡

Overview

Best Practices

Prefer Modern APIs

Code Style & Consistency

Deprecated Rules

Legend

Best Practices

Prefer Modern APIs

Code Style & Consistency

Build docs developers (and LLMs) love

Overview

Best Practices

Prefer Modern APIs

Code Style & Consistency

Deprecated Rules

Documentation Index

​Legend

​Best Practices

​Prefer Modern APIs

​Code Style & Consistency

Build docs developers (and LLMs) love

Legend

Best Practices

Prefer Modern APIs

Code Style & Consistency