Rules

Rules in ESLint are grouped by type to help you understand their purpose. Each rule has emojis denoting:

if the "extends": "eslint:recommended" property in a configuration file enables the rule

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

Possible Problems

These rules relate to possible logic errors in code:

		array-callback-return	enforce `return` statements in callbacks of array methods
✓		constructor-super	require `super()` calls in constructors
✓		for-direction	enforce "for" loop update clause moving the counter in the right direction.
✓		getter-return	enforce `return` statements in getters
✓		no-async-promise-executor	disallow using an async function as a Promise executor
		no-await-in-loop	disallow `await` inside of loops
✓		no-class-assign	disallow reassigning class members
✓		no-compare-neg-zero	disallow comparing against -0
✓		no-cond-assign	disallow assignment operators in conditional expressions
✓		no-const-assign	disallow reassigning `const` variables
		no-constant-binary-expression	disallow expressions where the operation doesn't affect the value
✓		no-constant-condition	disallow constant expressions in conditions
		no-constructor-return	disallow returning value from constructor
✓		no-control-regex	disallow control characters in regular expressions
✓		no-debugger	disallow the use of `debugger`
✓		no-dupe-args	disallow duplicate arguments in `function` definitions
✓		no-dupe-class-members	disallow duplicate class members
✓		no-dupe-else-if	disallow duplicate conditions in if-else-if chains
✓		no-dupe-keys	disallow duplicate keys in object literals
✓		no-duplicate-case	disallow duplicate case labels
		no-duplicate-imports	disallow duplicate module imports
✓		no-empty-character-class	disallow empty character classes in regular expressions
✓		no-empty-pattern	disallow empty destructuring patterns
✓		no-ex-assign	disallow reassigning exceptions in `catch` clauses
✓		no-fallthrough	disallow fallthrough of `case` statements
✓		no-func-assign	disallow reassigning `function` declarations
✓		no-import-assign	disallow assigning to imported bindings
✓		no-inner-declarations	disallow variable or `function` declarations in nested blocks
✓		no-invalid-regexp	disallow invalid regular expression strings in `RegExp` constructors
✓		no-irregular-whitespace	disallow irregular whitespace
✓		no-loss-of-precision	disallow literal numbers that lose precision
✓	💡	no-misleading-character-class	disallow characters which are made with multiple code points in character class syntax
✓		no-new-symbol	disallow `new` operators with the `Symbol` object
✓		no-obj-calls	disallow calling global object properties as functions
		no-promise-executor-return	disallow returning values from Promise executor functions
✓		no-prototype-builtins	disallow calling some `Object.prototype` methods directly on objects
✓		no-self-assign	disallow assignments where both sides are exactly the same
		no-self-compare	disallow comparisons where both sides are exactly the same
✓		no-setter-return	disallow returning values from setters
✓		no-sparse-arrays	disallow sparse arrays
		no-template-curly-in-string	disallow template literal placeholder syntax in regular strings
✓		no-this-before-super	disallow `this`/`super` before calling `super()` in constructors
✓		no-undef	disallow the use of undeclared variables unless mentioned in `/global /` comments
✓		no-unexpected-multiline	disallow confusing multiline expressions
		no-unmodified-loop-condition	disallow unmodified loop conditions
✓		no-unreachable	disallow unreachable code after `return`, `throw`, `continue`, and `break` statements
		no-unreachable-loop	disallow loops with a body that allows only one iteration
✓		no-unsafe-finally	disallow control flow statements in `finally` blocks
✓	💡	no-unsafe-negation	disallow negating the left operand of relational operators
✓		no-unsafe-optional-chaining	disallow use of optional chaining in contexts where the `undefined` value is not allowed
		no-unused-private-class-members	disallow unused private class members
✓		no-unused-vars	disallow unused variables
		no-use-before-define	disallow the use of variables before they are defined
✓		no-useless-backreference	disallow useless backreferences in regular expressions
		require-atomic-updates	disallow assignments that can lead to race conditions due to usage of `await` or `yield`
✓		use-isnan	require calls to `isNaN()` when checking for `NaN`
✓	💡	valid-typeof	enforce comparing `typeof` expressions against valid strings

Suggestions

These rules suggest alternate ways of doing things:

			accessor-pairs	enforce getter and setter pairs in objects and classes
	🔧		arrow-body-style	require braces around arrow function bodies
			block-scoped-var	enforce the use of variables within the scope they are defined
			camelcase	enforce camelcase naming convention
	🔧		capitalized-comments	enforce or disallow capitalization of the first letter of a comment
			class-methods-use-this	enforce that class methods utilize `this`
			complexity	enforce a maximum cyclomatic complexity allowed in a program
			consistent-return	require `return` statements to either always or never specify values
			consistent-this	enforce consistent naming when capturing the current execution context
	🔧		curly	enforce consistent brace style for all control statements
			default-case	require `default` cases in `switch` statements
			default-case-last	enforce default clauses in switch statements to be last
			default-param-last	enforce default parameters to be last
	🔧		dot-notation	enforce dot notation whenever possible
	🔧		eqeqeq	require the use of `===` and `!==`
			func-name-matching	require function names to match the name of the variable or property to which they are assigned
			func-names	require or disallow named `function` expressions
			func-style	enforce the consistent use of either `function` declarations or expressions
			grouped-accessor-pairs	require grouped accessor pairs in object literals and classes
			guard-for-in	require `for-in` loops to include an `if` statement
			id-denylist	disallow specified identifiers
			id-length	enforce minimum and maximum identifier lengths
			id-match	require identifiers to match a specified regular expression
			init-declarations	require or disallow initialization in variable declarations
			max-classes-per-file	enforce a maximum number of classes per file
			max-depth	enforce a maximum depth that blocks can be nested
			max-lines	enforce a maximum number of lines per file
			max-lines-per-function	enforce a maximum number of lines of code in a function
			max-nested-callbacks	enforce a maximum depth that callbacks can be nested
			max-params	enforce a maximum number of parameters in function definitions
			max-statements	enforce a maximum number of statements allowed in function blocks
	🔧		multiline-comment-style	enforce a particular style for multiline comments
			new-cap	require constructor names to begin with a capital letter
			no-alert	disallow the use of `alert`, `confirm`, and `prompt`
			no-array-constructor	disallow `Array` constructors
			no-bitwise	disallow bitwise operators
			no-caller	disallow the use of `arguments.caller` or `arguments.callee`
✓			no-case-declarations	disallow lexical declarations in case clauses
	🔧		no-confusing-arrow	disallow arrow functions where they could be confused with comparisons
			no-console	disallow the use of `console`
			no-continue	disallow `continue` statements
✓			no-delete-var	disallow deleting variables
	🔧		no-div-regex	disallow division operators explicitly at the beginning of regular expressions
	🔧		no-else-return	disallow `else` blocks after `return` statements in `if` statements
✓			no-empty	disallow empty block statements
			no-empty-function	disallow empty functions
			no-eq-null	disallow `null` comparisons without type-checking operators
			no-eval	disallow the use of `eval()`
			no-extend-native	disallow extending native types
	🔧		no-extra-bind	disallow unnecessary calls to `.bind()`
✓	🔧		no-extra-boolean-cast	disallow unnecessary boolean casts
	🔧		no-extra-label	disallow unnecessary labels
✓	🔧		no-extra-semi	disallow unnecessary semicolons
	🔧		no-floating-decimal	disallow leading or trailing decimal points in numeric literals
✓			no-global-assign	disallow assignments to native objects or read-only global variables
	🔧		no-implicit-coercion	disallow shorthand type conversions
			no-implicit-globals	disallow declarations in the global scope
			no-implied-eval	disallow the use of `eval()`-like methods
			no-inline-comments	disallow inline comments after code
			no-invalid-this	disallow use of `this` in contexts where the value of `this` is `undefined`
			no-iterator	disallow the use of the `__iterator__` property
			no-label-var	disallow labels that share a name with a variable
			no-labels	disallow labeled statements
			no-lone-blocks	disallow unnecessary nested blocks
	🔧		no-lonely-if	disallow `if` statements as the only statement in `else` blocks
			no-loop-func	disallow function declarations that contain unsafe references inside loop statements
			no-magic-numbers	disallow magic numbers
			no-mixed-operators	disallow mixed binary operators
			no-multi-assign	disallow use of chained assignment expressions
			no-multi-str	disallow multiline strings
			no-negated-condition	disallow negated conditions
			no-nested-ternary	disallow nested ternary expressions
			no-new	disallow `new` operators outside of assignments or comparisons
			no-new-func	disallow `new` operators with the `Function` object
			no-new-object	disallow `Object` constructors
			no-new-wrappers	disallow `new` operators with the `String`, `Number`, and `Boolean` objects
✓		💡	no-nonoctal-decimal-escape	disallow `\8` and `\9` escape sequences in string literals
✓			no-octal	disallow octal literals
			no-octal-escape	disallow octal escape sequences in string literals
			no-param-reassign	disallow reassigning `function` parameters
			no-plusplus	disallow the unary operators `++` and `--`
			no-proto	disallow the use of the `__proto__` property
✓			no-redeclare	disallow variable redeclaration
✓	🔧		no-regex-spaces	disallow multiple spaces in regular expressions
			no-restricted-exports	disallow specified names in exports
			no-restricted-globals	disallow specified global variables
			no-restricted-imports	disallow specified modules when loaded by `import`
			no-restricted-properties	disallow certain properties on certain objects
			no-restricted-syntax	disallow specified syntax
			no-return-assign	disallow assignment operators in `return` statements
			no-return-await	disallow unnecessary `return await`
			no-script-url	disallow `javascript:` urls
			no-sequences	disallow comma operators
			no-shadow	disallow variable declarations from shadowing variables declared in the outer scope
✓			no-shadow-restricted-names	disallow identifiers from shadowing restricted names
			no-ternary	disallow ternary operators
			no-throw-literal	disallow throwing literals as exceptions
	🔧		no-undef-init	disallow initializing variables to `undefined`
			no-undefined	disallow the use of `undefined` as an identifier
			no-underscore-dangle	disallow dangling underscores in identifiers
	🔧		no-unneeded-ternary	disallow ternary operators when simpler alternatives exist
			no-unused-expressions	disallow unused expressions
✓	🔧		no-unused-labels	disallow unused labels
			no-useless-call	disallow unnecessary calls to `.call()` and `.apply()`
✓			no-useless-catch	disallow unnecessary `catch` clauses
	🔧		no-useless-computed-key	disallow unnecessary computed property keys in objects and classes
			no-useless-concat	disallow unnecessary concatenation of literals or template literals
			no-useless-constructor	disallow unnecessary constructors
✓		💡	no-useless-escape	disallow unnecessary escape characters
	🔧		no-useless-rename	disallow renaming import, export, and destructured assignments to the same name
	🔧		no-useless-return	disallow redundant return statements
	🔧		no-var	require `let` or `const` instead of `var`
			no-void	disallow `void` operators
			no-warning-comments	disallow specified warning terms in comments
✓			no-with	disallow `with` statements
	🔧		object-shorthand	require or disallow method and property shorthand syntax for object literals
	🔧		one-var	enforce variables to be declared either together or separately in functions
	🔧		one-var-declaration-per-line	require or disallow newlines around variable declarations
	🔧		operator-assignment	require or disallow assignment operator shorthand where possible
	🔧		prefer-arrow-callback	require using arrow functions for callbacks
	🔧		prefer-const	require `const` declarations for variables that are never reassigned after declared
	🔧		prefer-destructuring	require destructuring from arrays and/or objects
	🔧		prefer-exponentiation-operator	disallow the use of `Math.pow` in favor of the `**` operator
			prefer-named-capture-group	enforce using named capture group in regular expression
	🔧		prefer-numeric-literals	disallow `parseInt()` and `Number.parseInt()` in favor of binary, octal, and hexadecimal literals
	🔧		prefer-object-has-own	disallow use of `Object.prototype.hasOwnProperty.call()` and prefer use of `Object.hasOwn()`
	🔧		prefer-object-spread	disallow using Object.assign with an object literal as the first argument and prefer the use of object spread instead.
			prefer-promise-reject-errors	require using Error objects as Promise rejection reasons
		💡	prefer-regex-literals	disallow use of the `RegExp` constructor in favor of regular expression literals
			prefer-rest-params	require rest parameters instead of `arguments`
			prefer-spread	require spread operators instead of `.apply()`
	🔧		prefer-template	require template literals instead of string concatenation
	🔧		quote-props	require quotes around object literal property names
		💡	radix	enforce the consistent use of the radix argument when using `parseInt()`
			require-await	disallow async functions which have no `await` expression
			require-unicode-regexp	enforce the use of `u` flag on RegExp
✓			require-yield	require generator functions to contain `yield`
	🔧		sort-imports	enforce sorted import declarations within modules
			sort-keys	require object keys to be sorted
	🔧		sort-vars	require variables within the same declaration block to be sorted
	🔧		spaced-comment	enforce consistent spacing after the `//` or `/*` in a comment
	🔧		strict	require or disallow strict mode directives
			symbol-description	require symbol descriptions
			vars-on-top	require `var` declarations be placed at the top of their containing scope
	🔧		yoda	require or disallow "Yoda" conditions

Layout & Formatting

These rules care about how the code looks rather than how it executes:

	🔧	array-bracket-newline	enforce linebreaks after opening and before closing array brackets
	🔧	array-bracket-spacing	enforce consistent spacing inside array brackets
	🔧	array-element-newline	enforce line breaks after each array element
	🔧	arrow-parens	require parentheses around arrow function arguments
	🔧	arrow-spacing	enforce consistent spacing before and after the arrow in arrow functions
	🔧	block-spacing	disallow or enforce spaces inside of blocks after opening block and before closing block
	🔧	brace-style	enforce consistent brace style for blocks
	🔧	comma-dangle	require or disallow trailing commas
	🔧	comma-spacing	enforce consistent spacing before and after commas
	🔧	comma-style	enforce consistent comma style
	🔧	computed-property-spacing	enforce consistent spacing inside computed property brackets
	🔧	dot-location	enforce consistent newlines before and after dots
	🔧	eol-last	require or disallow newline at the end of files
	🔧	func-call-spacing	require or disallow spacing between function identifiers and their invocations
	🔧	function-call-argument-newline	enforce line breaks between arguments of a function call
	🔧	function-paren-newline	enforce consistent line breaks inside function parentheses
	🔧	generator-star-spacing	enforce consistent spacing around `*` operators in generator functions
	🔧	implicit-arrow-linebreak	enforce the location of arrow function bodies
	🔧	indent	enforce consistent indentation
	🔧	jsx-quotes	enforce the consistent use of either double or single quotes in JSX attributes
	🔧	key-spacing	enforce consistent spacing between keys and values in object literal properties
	🔧	keyword-spacing	enforce consistent spacing before and after keywords
		line-comment-position	enforce position of line comments
	🔧	linebreak-style	enforce consistent linebreak style
	🔧	lines-around-comment	require empty lines around comments
	🔧	lines-between-class-members	require or disallow an empty line between class members
		max-len	enforce a maximum line length
		max-statements-per-line	enforce a maximum number of statements allowed per line
	🔧	multiline-ternary	enforce newlines between operands of ternary expressions
	🔧	new-parens	enforce or disallow parentheses when invoking a constructor with no arguments
	🔧	newline-per-chained-call	require a newline after each call in a method chain
	🔧	no-extra-parens	disallow unnecessary parentheses
✓		no-mixed-spaces-and-tabs	disallow mixed spaces and tabs for indentation
	🔧	no-multi-spaces	disallow multiple spaces
	🔧	no-multiple-empty-lines	disallow multiple empty lines
		no-tabs	disallow all tabs
	🔧	no-trailing-spaces	disallow trailing whitespace at the end of lines
	🔧	no-whitespace-before-property	disallow whitespace before properties
	🔧	nonblock-statement-body-position	enforce the location of single-line statements
	🔧	object-curly-newline	enforce consistent line breaks after opening and before closing braces
	🔧	object-curly-spacing	enforce consistent spacing inside braces
	🔧	object-property-newline	enforce placing object properties on separate lines
	🔧	operator-linebreak	enforce consistent linebreak style for operators
	🔧	padded-blocks	require or disallow padding within blocks
	🔧	padding-line-between-statements	require or disallow padding lines between statements
	🔧	quotes	enforce the consistent use of either backticks, double, or single quotes
	🔧	rest-spread-spacing	enforce spacing between rest and spread operators and their expressions
	🔧	semi	require or disallow semicolons instead of ASI
	🔧	semi-spacing	enforce consistent spacing before and after semicolons
	🔧	semi-style	enforce location of semicolons
	🔧	space-before-blocks	enforce consistent spacing before blocks
	🔧	space-before-function-paren	enforce consistent spacing before `function` definition opening parenthesis
	🔧	space-in-parens	enforce consistent spacing inside parentheses
	🔧	space-infix-ops	require spacing around infix operators
	🔧	space-unary-ops	enforce consistent spacing before or after unary operators
	🔧	switch-colon-spacing	enforce spacing around colons of switch statements
	🔧	template-curly-spacing	require or disallow spacing around embedded expressions of template strings
	🔧	template-tag-spacing	require or disallow spacing between template tags and their literals
	🔧	unicode-bom	require or disallow Unicode byte order mark (BOM)
	🔧	wrap-iife	require parentheses around immediate `function` invocations
	🔧	wrap-regex	require parenthesis around regex literals
	🔧	yield-star-spacing	require or disallow spacing around the `` in `yield` expressions

Deprecated

These rules have been deprecated in accordance with the deprecation policy, and replaced by newer rules:

Deprecated rule	Replaced by
callback-return	(no replacement)
global-require	(no replacement)
handle-callback-err	(no replacement)
id-blacklist	id-denylist
indent-legacy	indent
lines-around-directive	padding-line-between-statements
newline-after-var	padding-line-between-statements
newline-before-return	padding-line-between-statements
no-buffer-constructor	(no replacement)
no-catch-shadow	no-shadow
no-mixed-requires	(no replacement)
no-native-reassign	no-global-assign
no-negated-in-lhs	no-unsafe-negation
no-new-require	(no replacement)
no-path-concat	(no replacement)
no-process-env	(no replacement)
no-process-exit	(no replacement)
no-restricted-modules	(no replacement)
no-spaced-func	func-call-spacing
no-sync	(no replacement)
prefer-reflect	(no replacement)
require-jsdoc	(no replacement)
valid-jsdoc	(no replacement)

Removed

These rules from older versions of ESLint (before the deprecation policy existed) have been replaced by newer rules:

Removed rule	Replaced by
generator-star	generator-star-spacing
global-strict	strict
no-arrow-condition	no-confusing-arrow no-constant-condition
no-comma-dangle	comma-dangle
no-empty-class	no-empty-character-class
no-empty-label	no-labels
no-extra-strict	strict
no-reserved-keys	quote-props
no-space-before-semi	semi-spacing
no-wrap-func	no-extra-parens
space-after-function-name	space-before-function-paren
space-after-keywords	keyword-spacing
space-before-function-parentheses	space-before-function-paren
space-before-keywords	keyword-spacing
space-in-brackets	object-curly-spacing array-bracket-spacing
space-return-throw-case	keyword-spacing
space-unary-word-ops	space-unary-ops
spaced-line-comment	spaced-comment