README.md

ESLint Plugin TypeScript

An ESLint plugin which provides lint rules for TypeScript codebases.

Getting Started

• You can find our Getting Started docs here
• You can find our FAQ / Troubleshooting docs here

These docs walk you through setting up ESLint, this plugin, and our parser. If you know what you're doing and just want to quick start, read on...

Quick-start

Installation

Make sure you have TypeScript and @typescript-eslint/parser installed:

$ yarn add -D typescript @typescript-eslint/parser
$ npm i --save-dev typescript @typescript-eslint/parser

Then install the plugin:

$ yarn add -D @typescript-eslint/eslint-plugin
$ npm i --save-dev @typescript-eslint/eslint-plugin

It is important that you use the same version number for @typescript-eslint/parser and @typescript-eslint/eslint-plugin.

Note: If you installed ESLint globally (using the -g flag) then you must also install @typescript-eslint/eslint-plugin globally.

Usage

Add @typescript-eslint/parser to the parser field and @typescript-eslint to the plugins section of your .eslintrc configuration file, then configure the rules you want to use under the rules section.

{
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "rules": {
    "@typescript-eslint/rule-name": "error"
  }
}

You can also enable all the recommended rules for our plugin. Add plugin:@typescript-eslint/recommended in extends:

{
  "extends": ["plugin:@typescript-eslint/recommended"]
}

Recommended Configs

You can also use eslint:recommended (the set of rules which are recommended for all projects by the ESLint Team) with this plugin:

{
  "extends": ["eslint:recommended", "plugin:@typescript-eslint/recommended"]
}

As of version 2 of this plugin, by design, none of the rules in the main recommended config require type-checking in order to run. This means that they are more lightweight and faster to run.

Some highly valuable rules require type-checking in order to be implemented correctly, however, so we provide an additional config you can extend from called recommended-requiring-type-checking. You would apply this in addition to the recommended configs previously mentioned, e.g.:

{
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended",
    "plugin:@typescript-eslint/recommended-requiring-type-checking"
  ]
}

Pro Tip: For larger codebases you may want to consider splitting our linting into two separate stages: 1. fast feedback rules which operate purely based on syntax (no type-checking), 2. rules which are based on semantics (type-checking).

You can read more about linting with type information here

Supported Rules

Key: ✅ = recommended, 🔒 = strict, 🔧 = fixable, 💭 = requires type information

Name	Description	✅🔒	🔧	💭
@typescript-eslint/adjacent-overload-signatures	Require that member overloads be consecutive	✅
@typescript-eslint/array-type	Require using either T[] or Array<T> for arrays	🔒	🔧
@typescript-eslint/await-thenable	Disallow awaiting a value that is not a Thenable	✅		💭
@typescript-eslint/ban-ts-comment	Disallow @ts-<directive> comments or require descriptions after directive	✅
@typescript-eslint/ban-tslint-comment	Disallow // tslint:<rule-flag> comments	🔒	🔧
@typescript-eslint/ban-types	Disallow certain types	✅	🔧
@typescript-eslint/class-literal-property-style	Enforce that literals on classes are exposed in a consistent style	🔒	🔧
@typescript-eslint/consistent-generic-constructors	Enforce specifying generic type arguments on type annotation or constructor name of a constructor call	🔒	🔧
@typescript-eslint/consistent-indexed-object-style	Require or disallow the Record type	🔒	🔧
@typescript-eslint/consistent-type-assertions	Enforce consistent usage of type assertions	🔒
@typescript-eslint/consistent-type-definitions	Enforce type definitions to consistently use either interface or type	🔒	🔧
@typescript-eslint/consistent-type-exports	Enforce consistent usage of type exports		🔧	💭
@typescript-eslint/consistent-type-imports	Enforce consistent usage of type imports		🔧
@typescript-eslint/explicit-function-return-type	Require explicit return types on functions and class methods
@typescript-eslint/explicit-member-accessibility	Require explicit accessibility modifiers on class properties and methods		🔧
@typescript-eslint/explicit-module-boundary-types	Require explicit return and argument types on exported functions' and classes' public class methods
@typescript-eslint/member-delimiter-style	Require a specific member delimiter style for interfaces and type literals		🔧
@typescript-eslint/member-ordering	Require a consistent member declaration order
@typescript-eslint/method-signature-style	Enforce using a particular method signature syntax		🔧
@typescript-eslint/naming-convention	Enforce naming conventions for everything across a codebase			💭
@typescript-eslint/no-base-to-string	Require .toString() to only be called on objects which provide useful information when stringified	🔒		💭
@typescript-eslint/no-confusing-non-null-assertion	Disallow non-null assertion in locations that may be confusing	🔒	🔧
@typescript-eslint/no-confusing-void-expression	Require expressions of type void to appear in statement position		🔧	💭
@typescript-eslint/no-duplicate-enum-values	Disallow duplicate enum member values	🔒
@typescript-eslint/no-dynamic-delete	Disallow using the delete operator on computed key expressions	🔒	🔧
@typescript-eslint/no-empty-interface	Disallow the declaration of empty interfaces	✅	🔧
@typescript-eslint/no-explicit-any	Disallow the any type	✅	🔧
@typescript-eslint/no-extra-non-null-assertion	Disallow extra non-null assertion	✅	🔧
@typescript-eslint/no-extraneous-class	Disallow classes used as namespaces	🔒
@typescript-eslint/no-floating-promises	Require Promise-like statements to be handled appropriately	✅		💭
@typescript-eslint/no-for-in-array	Disallow iterating over an array with a for-in loop	✅		💭
@typescript-eslint/no-inferrable-types	Disallow explicit type declarations for variables or parameters initialized to a number, string, or boolean	✅	🔧
@typescript-eslint/no-invalid-void-type	Disallow void type outside of generic or return types	🔒
@typescript-eslint/no-meaningless-void-operator	Disallow the void operator except when used to discard a value	🔒	🔧	💭
@typescript-eslint/no-misused-new	Enforce valid definition of new and constructor	✅
@typescript-eslint/no-misused-promises	Disallow Promises in places not designed to handle them	✅		💭
@typescript-eslint/no-namespace	Disallow custom TypeScript modules and namespaces	✅
@typescript-eslint/no-non-null-asserted-nullish-coalescing	Disallow non-null assertions in the left operand of a nullish coalescing operator	🔒
@typescript-eslint/no-non-null-asserted-optional-chain	Disallow non-null assertions after an optional chain expression	✅
@typescript-eslint/no-non-null-assertion	Disallow non-null assertions using the ! postfix operator	✅
@typescript-eslint/no-redundant-type-constituents	Disallow members of unions and intersections that do nothing or override type information			💭
@typescript-eslint/no-require-imports	Disallow invocation of require()
@typescript-eslint/no-this-alias	Disallow aliasing this	✅
@typescript-eslint/no-type-alias	Disallow type aliases
@typescript-eslint/no-unnecessary-boolean-literal-compare	Disallow unnecessary equality comparisons against boolean literals	🔒	🔧	💭
@typescript-eslint/no-unnecessary-condition	Disallow conditionals where the type is always truthy or always falsy	🔒	🔧	💭
@typescript-eslint/no-unnecessary-qualifier	Disallow unnecessary namespace qualifiers		🔧	💭
@typescript-eslint/no-unnecessary-type-arguments	Disallow type arguments that are equal to the default	🔒	🔧	💭
@typescript-eslint/no-unnecessary-type-assertion	Disallow type assertions that do not change the type of an expression	✅	🔧	💭
@typescript-eslint/no-unnecessary-type-constraint	Disallow unnecessary constraints on generic types	✅
@typescript-eslint/no-unsafe-argument	Disallow calling a function with a value with type any	✅		💭
@typescript-eslint/no-unsafe-assignment	Disallow assigning a value with type any to variables and properties	✅		💭
@typescript-eslint/no-unsafe-call	Disallow calling a value with type any	✅		💭
@typescript-eslint/no-unsafe-member-access	Disallow member access on a value with type any	✅		💭
@typescript-eslint/no-unsafe-return	Disallow returning a value with type any from a function	✅		💭
@typescript-eslint/no-useless-empty-export	Disallow empty exports that don't change anything in a module file		🔧
@typescript-eslint/no-var-requires	Disallow require statements except in import statements	✅
@typescript-eslint/non-nullable-type-assertion-style	Enforce non-null assertions over explicit type casts	🔒	🔧	💭
@typescript-eslint/parameter-properties	Require or disallow parameter properties in class constructors
@typescript-eslint/prefer-as-const	Enforce the use of as const over literal type	✅	🔧
@typescript-eslint/prefer-enum-initializers	Require each enum member value to be explicitly initialized
@typescript-eslint/prefer-for-of	Enforce the use of for-of loop over the standard for loop where possible	🔒
@typescript-eslint/prefer-function-type	Enforce using function types instead of interfaces with call signatures	🔒	🔧
@typescript-eslint/prefer-includes	Enforce includes method over indexOf method	🔒	🔧	💭
@typescript-eslint/prefer-literal-enum-member	Require all enum members to be literal values	🔒
@typescript-eslint/prefer-namespace-keyword	Require using namespace keyword over module keyword to declare custom TypeScript modules	✅	🔧
@typescript-eslint/prefer-nullish-coalescing	Enforce using the nullish coalescing operator instead of logical chaining	🔒		💭
@typescript-eslint/prefer-optional-chain	Enforce using concise optional chain expressions instead of chained logical ands	🔒
@typescript-eslint/prefer-readonly	Require private members to be marked as readonly if they're never modified outside of the constructor		🔧	💭
@typescript-eslint/prefer-readonly-parameter-types	Require function parameters to be typed as readonly to prevent accidental mutation of inputs			💭
@typescript-eslint/prefer-reduce-type-parameter	Enforce using type parameter when calling Array#reduce instead of casting	🔒	🔧	💭
@typescript-eslint/prefer-regexp-exec	Enforce RegExp#exec over String#match if no global flag is provided		🔧	💭
@typescript-eslint/prefer-return-this-type	Enforce that this is used when only this type is returned	🔒	🔧	💭
@typescript-eslint/prefer-string-starts-ends-with	Enforce using String#startsWith and String#endsWith over other equivalent methods of checking substrings	🔒	🔧	💭
@typescript-eslint/prefer-ts-expect-error	Enforce using @ts-expect-error over @ts-ignore	🔒	🔧
@typescript-eslint/promise-function-async	Require any function or method that returns a Promise to be marked async		🔧	💭
@typescript-eslint/require-array-sort-compare	Require Array#sort calls to always provide a compareFunction			💭
@typescript-eslint/restrict-plus-operands	Require both operands of addition to have type number or string	✅		💭
@typescript-eslint/restrict-template-expressions	Enforce template literal expressions to be of string type	✅		💭
@typescript-eslint/sort-type-union-intersection-members	Enforce members of a type union/intersection to be sorted alphabetically		🔧
@typescript-eslint/strict-boolean-expressions	Disallow certain types in boolean expressions		🔧	💭
@typescript-eslint/switch-exhaustiveness-check	Require switch-case statements to be exhaustive with union type			💭
@typescript-eslint/triple-slash-reference	Disallow certain triple slash directives in favor of ES6-style import declarations	✅
@typescript-eslint/type-annotation-spacing	Require consistent spacing around type annotations		🔧
@typescript-eslint/typedef	Require type annotations in certain places
@typescript-eslint/unbound-method	Enforce unbound methods are called with their expected scope	✅		💭
@typescript-eslint/unified-signatures	Disallow two overloads that could be unified into one with a union or an optional/rest parameter	🔒

Extension Rules

In some cases, ESLint provides a rule itself, but it doesn't support TypeScript syntax; either it crashes, or it ignores the syntax, or it falsely reports against it. In these cases, we create what we call an extension rule; a rule within our plugin that has the same functionality, but also supports TypeScript.

Key: ✅ = recommended, 🔒 = strict, 🔧 = fixable, 💭 = requires type information

Name	Description	✅🔒	🔧	💭
@typescript-eslint/brace-style	Enforce consistent brace style for blocks		🔧
@typescript-eslint/comma-dangle	Require or disallow trailing commas		🔧
@typescript-eslint/comma-spacing	Enforce consistent spacing before and after commas		🔧
@typescript-eslint/default-param-last	Enforce default parameters to be last
@typescript-eslint/dot-notation	Enforce dot notation whenever possible	🔒	🔧	💭
@typescript-eslint/func-call-spacing	Require or disallow spacing between function identifiers and their invocations		🔧
@typescript-eslint/indent	Enforce consistent indentation		🔧
@typescript-eslint/init-declarations	Require or disallow initialization in variable declarations
@typescript-eslint/keyword-spacing	Enforce consistent spacing before and after keywords		🔧
@typescript-eslint/lines-between-class-members	Require or disallow an empty line between class members		🔧
@typescript-eslint/no-array-constructor	Disallow generic Array constructors	✅	🔧
@typescript-eslint/no-dupe-class-members	Disallow duplicate class members
@typescript-eslint/no-empty-function	Disallow empty functions	✅
@typescript-eslint/no-extra-parens	Disallow unnecessary parentheses		🔧
@typescript-eslint/no-extra-semi	Disallow unnecessary semicolons	✅	🔧
@typescript-eslint/no-implied-eval	Disallow the use of eval()-like methods	✅		💭
@typescript-eslint/no-invalid-this	Disallow this keywords outside of classes or class-like objects
@typescript-eslint/no-loop-func	Disallow function declarations that contain unsafe references inside loop statements
@typescript-eslint/no-loss-of-precision	Disallow literal numbers that lose precision	✅
@typescript-eslint/no-magic-numbers	Disallow magic numbers
@typescript-eslint/no-redeclare	Disallow variable redeclaration
@typescript-eslint/no-restricted-imports	Disallow specified modules when loaded by import
@typescript-eslint/no-shadow	Disallow variable declarations from shadowing variables declared in the outer scope
@typescript-eslint/no-throw-literal	Disallow throwing literals as exceptions	🔒		💭
@typescript-eslint/no-unused-expressions	Disallow unused expressions
@typescript-eslint/no-unused-vars	Disallow unused variables	✅
@typescript-eslint/no-use-before-define	Disallow the use of variables before they are defined
@typescript-eslint/no-useless-constructor	Disallow unnecessary constructors	🔒
@typescript-eslint/object-curly-spacing	Enforce consistent spacing inside braces		🔧
@typescript-eslint/padding-line-between-statements	Require or disallow padding lines between statements		🔧
@typescript-eslint/quotes	Enforce the consistent use of either backticks, double, or single quotes		🔧
@typescript-eslint/require-await	Disallow async functions which have no await expression	✅		💭
@typescript-eslint/return-await	Enforce consistent returning of awaited values		🔧	💭
@typescript-eslint/semi	Require or disallow semicolons instead of ASI		🔧
@typescript-eslint/space-before-blocks	Enforce consistent spacing before blocks		🔧
@typescript-eslint/space-before-function-paren	Enforce consistent spacing before function parenthesis		🔧
@typescript-eslint/space-infix-ops	Require spacing around infix operators		🔧

Contributing

See the contributing guide here.