Rules

Rules in ESLint are grouped by category to help you understand their purpose.

No rules are enabled by default. The "extends": "eslint:recommended" property in a configuration file enables rules that report common problems, which have a check mark below.

The `--fix` option on the command line automatically fixes problems (currently mostly whitespace) reported by rules which have a wrench below.

Possible Errors

These rules relate to possible syntax or logic errors in JavaScript code:

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-compare-neg-zero	disallow comparing against -0
no-cond-assign	disallow assignment operators in conditional expressions
no-console	disallow the use of `console`
no-constant-condition	disallow constant expressions in conditions
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-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-empty	disallow empty block statements
no-empty-character-class	disallow empty character classes in regular expressions
no-ex-assign	disallow reassigning exceptions in `catch` clauses
no-extra-boolean-cast	disallow unnecessary boolean casts
no-extra-parens	disallow unnecessary parentheses
no-extra-semi	disallow unnecessary semicolons
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-misleading-character-class	disallow characters which are made with multiple code points in character class syntax
no-obj-calls	disallow calling global object properties as functions
no-prototype-builtins	disallow calling some `Object.prototype` methods directly on objects
no-regex-spaces	disallow multiple spaces in regular expressions
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-unexpected-multiline	disallow confusing multiline expressions
no-unreachable	disallow unreachable code after `return`, `throw`, `continue`, and `break` statements
no-unsafe-finally	disallow control flow statements in `finally` blocks
no-unsafe-negation	disallow negating the left operand of relational operators
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

Best Practices

These rules relate to better ways of doing things to help you avoid problems:

accessor-pairs	enforce getter and setter pairs in objects and classes
array-callback-return	enforce `return` statements in callbacks of array methods
block-scoped-var	enforce the use of variables within the scope they are defined
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
curly	enforce consistent brace style for all control statements
default-case	require `default` cases in `switch` statements
default-param-last	enforce default parameters to be last
dot-location	enforce consistent newlines before and after dots
dot-notation	enforce dot notation whenever possible
eqeqeq	require the use of `===` and `!==`
grouped-accessor-pairs	require grouped accessor pairs in object literals and classes
guard-for-in	require `for-in` loops to include an `if` statement
max-classes-per-file	enforce a maximum number of classes per file
no-alert	disallow the use of `alert`, `confirm`, and `prompt`
no-caller	disallow the use of `arguments.caller` or `arguments.callee`
no-case-declarations	disallow lexical declarations in case clauses
no-constructor-return	disallow returning value from constructor
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-function	disallow empty functions
no-empty-pattern	disallow empty destructuring patterns
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-label	disallow unnecessary labels
no-fallthrough	disallow fallthrough of `case` statements
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-invalid-this	disallow `this` keywords outside of classes or class-like objects
no-iterator	disallow the use of the `__iterator__` property
no-labels	disallow labeled statements
no-lone-blocks	disallow unnecessary nested blocks
no-loop-func	disallow function declarations that contain unsafe references inside loop statements
no-magic-numbers	disallow magic numbers
no-multi-spaces	disallow multiple spaces
no-multi-str	disallow multiline strings
no-new	disallow `new` operators outside of assignments or comparisons
no-new-func	disallow `new` operators with the `Function` object
no-new-wrappers	disallow `new` operators with the `String`, `Number`, and `Boolean` objects
no-octal	disallow octal literals
no-octal-escape	disallow octal escape sequences in string literals
no-param-reassign	disallow reassigning `function` parameters
no-proto	disallow the use of the `__proto__` property
no-redeclare	disallow variable redeclaration
no-restricted-properties	disallow certain properties on certain objects
no-return-assign	disallow assignment operators in `return` statements
no-return-await	disallow unnecessary `return await`
no-script-url	disallow `javascript:` urls
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-sequences	disallow comma operators
no-throw-literal	disallow throwing literals as exceptions
no-unmodified-loop-condition	disallow unmodified loop conditions
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-concat	disallow unnecessary concatenation of literals or template literals
no-useless-escape	disallow unnecessary escape characters
no-useless-return	disallow redundant return statements
no-void	disallow `void` operators
no-warning-comments	disallow specified warning terms in comments
no-with	disallow `with` statements
prefer-named-capture-group	enforce using named capture group in regular expression
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
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
vars-on-top	require `var` declarations be placed at the top of their containing scope
wrap-iife	require parentheses around immediate `function` invocations
yoda	require or disallow "Yoda" conditions

Strict Mode

These rules relate to strict mode directives:

strict

require or disallow strict mode directives

Variables

These rules relate to variable declarations:

init-declarations	require or disallow initialization in variable declarations
no-delete-var	disallow deleting variables
no-label-var	disallow labels that share a name with a variable
no-restricted-globals	disallow specified global variables
no-shadow	disallow variable declarations from shadowing variables declared in the outer scope
no-shadow-restricted-names	disallow identifiers from shadowing restricted names
no-undef	disallow the use of undeclared variables unless mentioned in `/*global */` comments
no-undef-init	disallow initializing variables to `undefined`
no-undefined	disallow the use of `undefined` as an identifier
no-unused-vars	disallow unused variables
no-use-before-define	disallow the use of variables before they are defined

Node.js and CommonJS

These rules relate to code running in Node.js, or in browsers with CommonJS:

callback-return	require `return` statements after callbacks
global-require	require `require()` calls to be placed at top-level module scope
handle-callback-err	require error handling in callbacks
no-buffer-constructor	disallow use of the `Buffer()` constructor
no-mixed-requires	disallow `require` calls to be mixed with regular variable declarations
no-new-require	disallow `new` operators with calls to `require`
no-path-concat	disallow string concatenation with `__dirname` and `__filename`
no-process-env	disallow the use of `process.env`
no-process-exit	disallow the use of `process.exit()`
no-restricted-modules	disallow specified modules when loaded by `require`
no-sync	disallow synchronous methods

Stylistic Issues

These rules relate to style guidelines, and are therefore quite subjective:

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
block-spacing	disallow or enforce spaces inside of blocks after opening block and before closing block
brace-style	enforce consistent brace style for blocks
camelcase	enforce camelcase naming convention
capitalized-comments	enforce or disallow capitalization of the first letter of a comment
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
consistent-this	enforce consistent naming when capturing the current execution context
eol-last	require or disallow newline at the end of files
func-call-spacing	require or disallow spacing between function identifiers and their invocations
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
function-call-argument-newline	enforce line breaks between arguments of a function call
function-paren-newline	enforce consistent line breaks inside function parentheses
id-blacklist	disallow specified identifiers
id-length	enforce minimum and maximum identifier lengths
id-match	require identifiers to match a specified regular expression
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-depth	enforce a maximum depth that blocks can be nested
max-len	enforce a maximum line length
max-lines	enforce a maximum number of lines per file
max-lines-per-function	enforce a maximum number of line 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
max-statements-per-line	enforce a maximum number of statements allowed per line
multiline-comment-style	enforce a particular style for multiline comments
multiline-ternary	enforce newlines between operands of ternary expressions
new-cap	require constructor names to begin with a capital letter
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-array-constructor	disallow `Array` constructors
no-bitwise	disallow bitwise operators
no-continue	disallow `continue` statements
no-inline-comments	disallow inline comments after code
no-lonely-if	disallow `if` statements as the only statement in `else` blocks
no-mixed-operators	disallow mixed binary operators
no-mixed-spaces-and-tabs	disallow mixed spaces and tabs for indentation
no-multi-assign	disallow use of chained assignment expressions
no-multiple-empty-lines	disallow multiple empty lines
no-negated-condition	disallow negated conditions
no-nested-ternary	disallow nested ternary expressions
no-new-object	disallow `Object` constructors
no-plusplus	disallow the unary operators `++` and `--`
no-restricted-syntax	disallow specified syntax
no-tabs	disallow all tabs
no-ternary	disallow ternary operators
no-trailing-spaces	disallow trailing whitespace at the end of lines
no-underscore-dangle	disallow dangling underscores in identifiers
no-unneeded-ternary	disallow ternary operators when simpler alternatives exist
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 inside braces
object-curly-spacing	enforce consistent spacing inside braces
object-property-newline	enforce placing object properties on separate lines
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
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
prefer-exponentiation-operator	disallow the use of `Math.pow` in favor of the `**` operator
prefer-object-spread	disallow using Object.assign with an object literal as the first argument and prefer the use of object spread instead.
quote-props	require quotes around object literal property names
quotes	enforce the consistent use of either backticks, double, or single quotes
semi	require or disallow semicolons instead of ASI
semi-spacing	enforce consistent spacing before and after semicolons
semi-style	enforce location of semicolons
sort-keys	require object keys to be sorted
sort-vars	require variables within the same declaration block to be sorted
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
spaced-comment	enforce consistent spacing after the `//` or `/*` in a comment
switch-colon-spacing	enforce spacing around colons of switch statements
template-tag-spacing	require or disallow spacing between template tags and their literals
unicode-bom	require or disallow Unicode byte order mark (BOM)
wrap-regex	require parenthesis around regex literals

ECMAScript 6

These rules relate to ES6, also known as ES2015:

arrow-body-style	require braces around arrow function bodies
arrow-parens	require parentheses around arrow function arguments
arrow-spacing	enforce consistent spacing before and after the arrow in arrow functions
constructor-super	require `super()` calls in constructors
generator-star-spacing	enforce consistent spacing around `*` operators in generator functions
no-class-assign	disallow reassigning class members
no-confusing-arrow	disallow arrow functions where they could be confused with comparisons
no-const-assign	disallow reassigning `const` variables
no-dupe-class-members	disallow duplicate class members
no-duplicate-imports	disallow duplicate module imports
no-new-symbol	disallow `new` operators with the `Symbol` object
no-restricted-imports	disallow specified modules when loaded by `import`
no-this-before-super	disallow `this`/`super` before calling `super()` in constructors
no-useless-computed-key	disallow unnecessary computed property keys in objects and classes
no-useless-constructor	disallow unnecessary constructors
no-useless-rename	disallow renaming import, export, and destructured assignments to the same name
no-var	require `let` or `const` instead of `var`
object-shorthand	require or disallow method and property shorthand syntax for object literals
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-numeric-literals	disallow `parseInt()` and `Number.parseInt()` in favor of binary, octal, and hexadecimal 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
require-yield	require generator functions to contain `yield`
rest-spread-spacing	enforce spacing between rest and spread operators and their expressions
sort-imports	enforce sorted import declarations within modules
symbol-description	require symbol descriptions
template-curly-spacing	require or disallow spacing around embedded expressions of template strings
yield-star-spacing	require or disallow spacing around the `*` in `yield*` expressions

Deprecated

These rules have been deprecated in accordance with the [deprecation policy](/docs/user-guide/rule-deprecation), and replaced by newer rules:

Removed

These rules from older versions of ESLint (before the [deprecation policy](/docs/user-guide/rule-deprecation) existed) have been replaced by newer rules: