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": "latest",
            "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-await-expression-member": "error",
            "unicorn/no-console-spaces": "error",
            "unicorn/no-document-cookie": "error",
            "unicorn/no-empty-file": "error",
            "unicorn/no-for-loop": "error",
            "unicorn/no-hex-escape": "error",
            "unicorn/no-instanceof-array": "error",
            "unicorn/no-invalid-remove-event-listener": "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-thenable": "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-fallback-in-spread": "error",
            "unicorn/no-useless-length-check": "error",
            "unicorn/no-useless-promise-resolve-reject": "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-code-point": "error",
            "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-export-from": "error",
            "unicorn/prefer-includes": "error",
            "unicorn/prefer-json-parse-buffer": "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-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/relative-url-style": "error",
            "unicorn/require-array-join-separator": "error",
            "unicorn/require-number-to-fixed-digits-argument": "error",
            "unicorn/require-post-message-target-origin": "off",
            "unicorn/string-content": "off",
            "unicorn/template-indent": "warn",
            "unicorn/throw-new-error": "error"
        }
    }
}

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-await-expression-member	Forbid member access from await expression.	✅	🔧
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-array	Require Array.isArray() instead of instanceof Array.	✅	🔧
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-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-thenable	Disallow then property.	✅
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-fallback-in-spread	Forbid 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-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-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-export-from	Prefer export…from when re-exporting.	✅	🔧	💡
prefer-includes	Prefer .includes() over .indexOf() 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-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-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(…), Array#slice() and String#split('').	✅	🔧	💡
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.	✅	🔧
relative-url-style	Enforce consistent relative URL style.	✅	🔧
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.		🔧	💡
template-indent	Fix whitespace-insensitive template indentation.	✅	🔧
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.

All config

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

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

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

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

Maintainers

• Sindre Sorhus
• Fisker Cheung
• Bryan Mishkin
• futpib

Former

• Jeroen Engels
• Sam Verschueren
• Adam Babcock