ESLINT - PLUGGABLE JAVASCRIPT LINTERRULESGET STARTEDUSER GUIDECOMMAND LINE INTERFACEWORKING WITH CUSTOM FORMATTERSDEMO A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

NO-THROW-LITERAL

A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease. NO-RESTRICTED-SYNTAX MAX-LEN - RULES - ESLINT - PLUGGABLE JAVASCRIPT LINTERSEE MORE ON

ESLINT.ORG

PREFER-OBJECT-SPREAD Prefer use of an object spread over. Object.assign. (prefer-object-spread) The --fix option on the command line can automatically fix some of the problems reported by this rule. When Object.assign is called using an object literal as the first argument, this rule requires using the object spread syntax instead. This rule

also warns on cases

GUARD-FOR-IN

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement. Examples of incorrect code for this rule: /*eslint guard-for-in: "error"*/ for (key in foo) { doSomething (key

NO-DUPE-ELSE-IF

chains (no-dupe-else-if) The "extends": "eslint:recommended" property in a configuration file enables this rule. if-else-if chains are commonly used when there is a need to execute only one branch (or at most one branch) out of several possible branches, based on certain conditions. Two identical test conditions in the same chain are almost NO-ASYNC-PROMISE-EXECUTOR disallow using an async function as a Promise executor (no-async-promise-executor) The "extends": "eslint:recommended" property in a configuration file enables this rule. The new Promise constructor accepts an executor function as an argument, which has resolve and reject parameters that can be used to control the state of the created Promise. NO-UNDERSCORE-DANGLE NO-TEMPLATE-CURLY-IN-STRING Disallow template literal placeholder syntax in regular strings (no-template-curly-in-string) ECMAScript 6 allows programmers to create strings containing variable or expressions using template literals, instead of string concatenation, by writing expressions like ${variable} between two backtick quotes (`). It can be easy to use the wrong quotes when wanting to use template literals, by ESLINT - PLUGGABLE JAVASCRIPT LINTERRULESGET STARTEDUSER GUIDECOMMAND LINE INTERFACEWORKING WITH CUSTOM FORMATTERSDEMO A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

NO-THROW-LITERAL

A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease. NO-RESTRICTED-SYNTAX MAX-LEN - RULES - ESLINT - PLUGGABLE JAVASCRIPT LINTERSEE MORE ON

ESLINT.ORG

PREFER-OBJECT-SPREAD Prefer use of an object spread over. Object.assign. (prefer-object-spread) The --fix option on the command line can automatically fix some of the problems reported by this rule. When Object.assign is called using an object literal as the first argument, this rule requires using the object spread syntax instead. This rule

also warns on cases

GUARD-FOR-IN

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement. Examples of incorrect code for this rule: /*eslint guard-for-in: "error"*/ for (key in foo) { doSomething (key

NO-DUPE-ELSE-IF

chains (no-dupe-else-if) The "extends": "eslint:recommended" property in a configuration file enables this rule. if-else-if chains are commonly used when there is a need to execute only one branch (or at most one branch) out of several possible branches, based on certain conditions. Two identical test conditions in the same chain are almost NO-ASYNC-PROMISE-EXECUTOR disallow using an async function as a Promise executor (no-async-promise-executor) The "extends": "eslint:recommended" property in a configuration file enables this rule. The new Promise constructor accepts an executor function as an argument, which has resolve and reject parameters that can be used to control the state of the created Promise. NO-UNDERSCORE-DANGLE NO-TEMPLATE-CURLY-IN-STRING Disallow template literal placeholder syntax in regular strings (no-template-curly-in-string) ECMAScript 6 allows programmers to create strings containing variable or expressions using template literals, instead of string concatenation, by writing expressions like ${variable} between two backtick quotes (`). It can be easy to use the wrong quotes when wanting to use template literals, by ESLINT V7.28.0 RELEASED ESLint v7.28.0 released. We just pushed ESLint v7.28.0, which is a minor release upgrade of ESLint. This release adds some new features and fixes several bugs found in the previous release. WHAT'S COMING IN ESLINT V8.0.0 What's coming in ESLint v8.0.0. Last week, the Technical Steering Committee (TSC) met to finalize the features for ESLint v8.0.0. This feature set had not yet been locked down even as v8.0.0 work began and so this represented an important milestone that SUPPORTING ESLINT'S DEPENDENCIES Eleventy is a Node.js-based static site generator that we use to create eslint.org. Sindre Sorhus is a prolific open source developer, and ESLint uses several of his modules, including chalk, globals, import-fresh, strip-ansi, and strip-json-comments. We're grateful to these projects, and all of our dependencies, for allowing us to build

ESLint.

OBJECT-SHORTHAND

Require Object Literal Shorthand Syntax (object-shorthand) The --fix option on the command line can automatically fix some of the problems reported by this rule.. ECMAScript 6 provides a concise form for defining object literal methods and properties. CLASS-METHODS-USE-THIS Enforce that class methods utilize this (class-methods-use-this). If a class method does not use this, it can sometimes be made into a static function. If you do convert the method into a static function, instances of the class that call that particular method have to be converted to a static call as well (MyClass.callStaticMethod())It's possible to have a class method which doesn't use this

NO-PLUSPLUS

A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

NO-AWAIT-IN-LOOP

Disallow await inside of loops (no-await-in-loop). Performing an operation on each element of an iterable is a common task. However, performing an await as part of each operation is an indication that the program is not taking full advantage of the parallelization benefits of async/await.. Usually, the code should be refactored to create all the promises at once, then get access to the results

PREFER-TEMPLATE

Suggest using template literals instead of string concatenation. (prefer-template) The --fix option on the command line can automatically fix some of the problems reported by this rule. In ES2015 (ES6), we can use template literals instead of string concatenation. var str = "Hello, " + name + "!"; NO-TEMPLATE-CURLY-IN-STRING Disallow template literal placeholder syntax in regular strings (no-template-curly-in-string) ECMAScript 6 allows programmers to create strings containing variable or expressions using template literals, instead of string concatenation, by writing expressions like ${variable} between two backtick quotes (`). It can be easy to use the wrong quotes when wanting to use template literals, by

NO-PARAM-REASSIGN

Rule Details. This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters. Examples of incorrect code for this rule: /*eslint no-param-reassign: "error"*/ function foo(bar) { bar = 13; } function foo(bar) { bar++; } function foo(bar) { for (bar in baz) {} } function foo(bar) { for (bar of baz ESLINT - PLUGGABLE JAVASCRIPT LINTERRULESGET STARTEDUSER GUIDECOMMAND LINE INTERFACEWORKING WITH CUSTOM FORMATTERSDEMO A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

NO-THROW-LITERAL

A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease. NO-RESTRICTED-SYNTAX MAX-LEN - RULES - ESLINT - PLUGGABLE JAVASCRIPT LINTERSEE MORE ON

ESLINT.ORG

PREFER-OBJECT-SPREAD Prefer use of an object spread over. Object.assign. (prefer-object-spread) The --fix option on the command line can automatically fix some of the problems reported by this rule. When Object.assign is called using an object literal as the first argument, this rule requires using the object spread syntax instead. This rule

also warns on cases

GUARD-FOR-IN

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement. Examples of incorrect code for this rule: /*eslint guard-for-in: "error"*/ for (key in foo) { doSomething (key

NO-DUPE-ELSE-IF

chains (no-dupe-else-if) The "extends": "eslint:recommended" property in a configuration file enables this rule. if-else-if chains are commonly used when there is a need to execute only one branch (or at most one branch) out of several possible branches, based on certain conditions. Two identical test conditions in the same chain are almost NO-ASYNC-PROMISE-EXECUTOR disallow using an async function as a Promise executor (no-async-promise-executor) The "extends": "eslint:recommended" property in a configuration file enables this rule. The new Promise constructor accepts an executor function as an argument, which has resolve and reject parameters that can be used to control the state of the created Promise. NO-UNDERSCORE-DANGLE NO-TEMPLATE-CURLY-IN-STRING Disallow template literal placeholder syntax in regular strings (no-template-curly-in-string) ECMAScript 6 allows programmers to create strings containing variable or expressions using template literals, instead of string concatenation, by writing expressions like ${variable} between two backtick quotes (`). It can be easy to use the wrong quotes when wanting to use template literals, by ESLINT - PLUGGABLE JAVASCRIPT LINTERRULESGET STARTEDUSER GUIDECOMMAND LINE INTERFACEWORKING WITH CUSTOM FORMATTERSDEMO A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

NO-THROW-LITERAL

A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease. NO-RESTRICTED-SYNTAX MAX-LEN - RULES - ESLINT - PLUGGABLE JAVASCRIPT LINTERSEE MORE ON

ESLINT.ORG

PREFER-OBJECT-SPREAD Prefer use of an object spread over. Object.assign. (prefer-object-spread) The --fix option on the command line can automatically fix some of the problems reported by this rule. When Object.assign is called using an object literal as the first argument, this rule requires using the object spread syntax instead. This rule

also warns on cases

GUARD-FOR-IN

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement. Examples of incorrect code for this rule: /*eslint guard-for-in: "error"*/ for (key in foo) { doSomething (key

NO-DUPE-ELSE-IF

chains (no-dupe-else-if) The "extends": "eslint:recommended" property in a configuration file enables this rule. if-else-if chains are commonly used when there is a need to execute only one branch (or at most one branch) out of several possible branches, based on certain conditions. Two identical test conditions in the same chain are almost NO-ASYNC-PROMISE-EXECUTOR disallow using an async function as a Promise executor (no-async-promise-executor) The "extends": "eslint:recommended" property in a configuration file enables this rule. The new Promise constructor accepts an executor function as an argument, which has resolve and reject parameters that can be used to control the state of the created Promise. NO-UNDERSCORE-DANGLE NO-TEMPLATE-CURLY-IN-STRING Disallow template literal placeholder syntax in regular strings (no-template-curly-in-string) ECMAScript 6 allows programmers to create strings containing variable or expressions using template literals, instead of string concatenation, by writing expressions like ${variable} between two backtick quotes (`). It can be easy to use the wrong quotes when wanting to use template literals, by ESLINT V7.28.0 RELEASED ESLint v7.28.0 released. We just pushed ESLint v7.28.0, which is a minor release upgrade of ESLint. This release adds some new features and fixes several bugs found in the previous release. WHAT'S COMING IN ESLINT V8.0.0 What's coming in ESLint v8.0.0. Last week, the Technical Steering Committee (TSC) met to finalize the features for ESLint v8.0.0. This feature set had not yet been locked down even as v8.0.0 work began and so this represented an important milestone that SUPPORTING ESLINT'S DEPENDENCIES Eleventy is a Node.js-based static site generator that we use to create eslint.org. Sindre Sorhus is a prolific open source developer, and ESLint uses several of his modules, including chalk, globals, import-fresh, strip-ansi, and strip-json-comments. We're grateful to these projects, and all of our dependencies, for allowing us to build

ESLint.

OBJECT-SHORTHAND

Require Object Literal Shorthand Syntax (object-shorthand) The --fix option on the command line can automatically fix some of the problems reported by this rule.. ECMAScript 6 provides a concise form for defining object literal methods and properties. CLASS-METHODS-USE-THIS Enforce that class methods utilize this (class-methods-use-this). If a class method does not use this, it can sometimes be made into a static function. If you do convert the method into a static function, instances of the class that call that particular method have to be converted to a static call as well (MyClass.callStaticMethod())It's possible to have a class method which doesn't use this

NO-PLUSPLUS

A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

NO-AWAIT-IN-LOOP

Disallow await inside of loops (no-await-in-loop). Performing an operation on each element of an iterable is a common task. However, performing an await as part of each operation is an indication that the program is not taking full advantage of the parallelization benefits of async/await.. Usually, the code should be refactored to create all the promises at once, then get access to the results

PREFER-TEMPLATE

Suggest using template literals instead of string concatenation. (prefer-template) The --fix option on the command line can automatically fix some of the problems reported by this rule. In ES2015 (ES6), we can use template literals instead of string concatenation. var str = "Hello, " + name + "!"; NO-TEMPLATE-CURLY-IN-STRING Disallow template literal placeholder syntax in regular strings (no-template-curly-in-string) ECMAScript 6 allows programmers to create strings containing variable or expressions using template literals, instead of string concatenation, by writing expressions like ${variable} between two backtick quotes (`). It can be easy to use the wrong quotes when wanting to use template literals, by

NO-PARAM-REASSIGN

Rule Details. This rule aims to prevent unintended behavior caused by modification or reassignment of function parameters. Examples of incorrect code for this rule: /*eslint no-param-reassign: "error"*/ function foo(bar) { bar = 13; } function foo(bar) { bar++; } function foo(bar) { for (bar in baz) {} } function foo(bar) { for (bar of baz ESLINT - PLUGGABLE JAVASCRIPT LINTERRULESGET STARTEDUSER GUIDECOMMAND LINE INTERFACEWORKING WITH CUSTOM FORMATTERSDEMO A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

COMMA-DANGLE

require or disallow trailing commas (comma-dangle) The --fix option on the command line can automatically fix some of the problems reported by this rule.. Trailing commas in object literals are valid according to the ECMAScript 5 (and ECMAScript 3!) spec. COMMAND LINE INTERFACE NO-INNER-DECLARATIONS CLASS-METHODS-USE-THIS

NO-CONTINUE

Close search. disallow continue statements (no-continue). The continue statement terminates execution of the statements in the current iteration of the current or labeled loop, and continues execution of the loop with the next iteration. When used incorrectly it makes

NO-EXTRA-PARENS

NO-RESTRICTED-SYNTAX PREFER-OBJECT-SPREAD Prefer use of an object spread over Object.assign (prefer-object-spread). The --fix option on the command line can automatically fix some of the problems reported by this rule.. When Object.assign is called using an object literal as the first argument, this rule requires using the object spread syntax instead. NO-UNDERSCORE-DANGLE ESLINT - PLUGGABLE JAVASCRIPT LINTERRULESGET STARTEDUSER GUIDECOMMAND LINE INTERFACEWORKING WITH CUSTOM FORMATTERSDEMO A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

COMMA-DANGLE

require or disallow trailing commas (comma-dangle) The --fix option on the command line can automatically fix some of the problems reported by this rule.. Trailing commas in object literals are valid according to the ECMAScript 5 (and ECMAScript 3!) spec. COMMAND LINE INTERFACE NO-INNER-DECLARATIONS CLASS-METHODS-USE-THIS

NO-CONTINUE

Close search. disallow continue statements (no-continue). The continue statement terminates execution of the statements in the current iteration of the current or labeled loop, and continues execution of the loop with the next iteration. When used incorrectly it makes

NO-EXTRA-PARENS

NO-RESTRICTED-SYNTAX PREFER-OBJECT-SPREAD Prefer use of an object spread over Object.assign (prefer-object-spread). The --fix option on the command line can automatically fix some of the problems reported by this rule.. When Object.assign is called using an object literal as the first argument, this rule requires using the object spread syntax instead. NO-UNDERSCORE-DANGLE ESLINT V7.28.0 RELEASED ESLint v7.28.0 released. We just pushed ESLint v7.28.0, which is a minor release upgrade of ESLint. This release adds some new features and fixes several bugs found in the previous release. COMMAND LINE INTERFACE A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease. QUOTES - RULES - ESLINT - PLUGGABLE JAVASCRIPT LINTER enforce the consistent use of either backticks, double, or single quotes (quotes) The --fix option on the command line can automatically fix some of the problems reported by this rule.. JavaScript allows you to define strings in one of three ways: double quotes, single quotes, and backticks (as of ECMAScript 6).

ARROW-PARENS

Close search. Require parens in arrow function arguments (arrow-parens) The --fix option on the command line can automatically fix some of the problems reported by this rule.. Arrow functions can omit parentheses when they have exactly one parameter. SEMI - RULES - ESLINT - PLUGGABLE JAVASCRIPT LINTER A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease.

NO-PLUSPLUS

Close search. disallow the unary operators ++ and --(no-plusplus). Because the unary ++ and --operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code.. var i = 10; var j = 20; i ++ j // i = 11, j = 20 var i = 10; var j = 20; i ++ j // i = 10, j = 21 Rule Details. This rule disallows the unary operators ++ and --. NO-INNER-DECLARATIONS disallow variable or function declarations in nested blocks (no-inner-declarations). The "extends": "eslint:recommended" property in a configuration file enables this rule.. In JavaScript, prior to ES6, a function declaration is only allowed in the first level of a program or the body of another function, though parsers sometimes erroneously accept them elsewhere. NO-ALERT - RULES - ESLINT - PLUGGABLE JAVASCRIPT LINTER A pluggable and configurable linter tool for identifying and reporting on patterns in JavaScript. Maintain your code quality with ease. NO-RESTRICTED-SYNTAX disallow specified syntax (no-restricted-syntax) JavaScript has a lot of language features, and not everyone likes all of them. As a result, some projects choose to disallow the use of certain language features

altogether.

DEFAULT-CASE-LAST

Enforce default clauses in switch statements to be last (default-case-last) A switch statement can optionally have a default clause.. If present, it's usually the last clause, but it doesn't need

to be.

ESLint

Toggle navigation Open search

* User guide

* Getting Started

* Configuring ESLint * Command Line Interface

* Rules

* Formatters

* Integrations

*

* Migrating to v1.0.0 * Migrating to v2.0.0 * Migrating to v3.0.0 * Migrating to v4.0.0 * Migrating to v5.0.0 * Migrating to v6.0.0 * Migrating from JSCS

* Developer guide

* Architecture

* Contributing

* Get the Source Code * Set up a Development Environment * Run the Unit Tests * Working with Rules * Working with Plugins * Working with Custom Formatters * Working with Custom Parsers

* Shareable Configs

* Node.js API

* Maintainer guide

* Blog

* Demo

* ESLint Demo

* Espree Demo

* About

* Who's Using ESLint?

* About the Team

* About ESLint

Open search

Search

Close search

ESLINT

THE PLUGGABLE LINTING UTILITY FOR JAVASCRIPT AND JSX

Get Started »

WELCOME

ESLint is an open source project originally created by Nicholas C. Zakas in June 2013. Its goal is to provide a pluggable linting utility for JavaScript.

LATEST NEWS

* ESLint v6.5.1 released 30

September 2019

-------------------------

ABOUT

Learn more about ESLint and why it came about and the general philosophy behind it.

Learn More »

RULES

ESLint comes with a bunch of default rules to get you started. This is

the complete list.

See List »

COMMAND LINE INTERFACE ESLint is written to be used primarily on the command line. Learn about its usage here.

CLI Details »

DEVELOPER GUIDE

Love ESLint and want to help make it even awesomer? We've got all the details to get you started.

Start Hacking »

-------------------------

SPONSORS

The following companies, organizations, and individuals support ESLint's ongoing maintenance and development.

GOLD SPONSORS

Become a Sponsor

SILVER SPONSORS

Become a Sponsor

BRONZE SPONSORS

Become a Sponsor

HOSTING

------------------------- ESLint requires Node.js and works on Windows, Mac

and Linux

-------------------------

* Edit this page

* Mailing List

* GitHub

* Twitter

* Chat Room

* Copyright JS Foundation and other contributors, https://js.foundation/