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-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 `this` keywords outside of classes or class-like objects
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-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:

Removed

These rules from older versions of ESLint (before the deprecation policy existed) have been replaced by newer rules: