ESLintRules
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. | ||
| 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-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-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 outside of strings and comments | |
| ✓ | 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-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 |
| ✓ | use-isnan | require calls to `isNaN()` when checking for `NaN` | |
| valid-jsdoc | enforce valid JSDoc comments | ||
| ✓ | 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 | ||
| 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 | ||
| 🔧 | dot-location | enforce consistent newlines before and after dots | |
| 🔧 | dot-notation | enforce dot notation whenever possible | |
| 🔧 | eqeqeq | require the use of `===` and `!==` | |
| guard-for-in | require `for-in` loops to include an `if` statement | ||
| 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-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 variable and `function` 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 and expressions 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-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-promise-reject-errors | require using Error objects as Promise rejection reasons | ||
| radix | enforce the consistent use of the radix argument when using `parseInt()` | ||
| require-await | disallow async functions which have no `await` expression | ||
| 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-catch-shadow | disallow `catch` clause parameters from shadowing variables in the outer scope | ||
| ✓ | 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 | enforce consistent spacing inside single-line blocks | |
| 🔧 | 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 | ||
| id-blacklist | disallow specified identifiers | ||
| id-length | enforce minimum and maximum identifier lengths | ||
| id-match | require identifiers to match a specified regular expression | ||
| 🔧 | 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 | |
| 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-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-ternary | enforce newlines between operands of ternary expressions | ||
| new-cap | require constructor names to begin with a capital letter | ||
| 🔧 | new-parens | require 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 | |
| 🔧 | quote-props | require quotes around object literal property names | |
| 🔧 | quotes | enforce the consistent use of either backticks, double, or single quotes | |
| require-jsdoc | require JSDoc comments | ||
| 🔧 | 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 object literals | |
| 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 arrow functions as 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()` 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, 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) |