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"]
}

Note: Make sure to use eslint --ext .js,.ts since by default eslint will only search for .js files.

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 simply 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, 🔧 = fixable, 💭 = requires type information

Name	Description	✅	🔧	💭
@typescript-eslint/adjacent-overload-signatures	Require that member overloads be consecutive	✅
@typescript-eslint/array-type	Requires using either T[] or Array<T> for arrays		🔧
@typescript-eslint/await-thenable	Disallows awaiting a value that is not a Thenable	✅		💭
@typescript-eslint/ban-ts-comment	Bans @ts-<directive> comments from being used or requires descriptions after directive	✅
@typescript-eslint/ban-tslint-comment	Bans // tslint:<rule-flag> comments from being used		🔧
@typescript-eslint/ban-types	Bans specific types from being used	✅	🔧
@typescript-eslint/class-literal-property-style	Ensures that literals on classes are exposed in a consistent style		🔧
@typescript-eslint/consistent-indexed-object-style	Enforce or disallow the use of the record type		🔧
@typescript-eslint/consistent-type-assertions	Enforces consistent usage of type assertions
@typescript-eslint/consistent-type-definitions	Consistent with type definition either interface or type		🔧
@typescript-eslint/consistent-type-imports	Enforces 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	Enforces using a particular method signature syntax.		🔧
@typescript-eslint/naming-convention	Enforces naming conventions for everything across a codebase			💭
@typescript-eslint/no-base-to-string	Requires that .toString() is only 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	Requires expressions of type void to appear in statement position		🔧	💭
@typescript-eslint/no-dynamic-delete	Disallow the delete operator with computed key expressions		🔧
@typescript-eslint/no-empty-interface	Disallow the declaration of empty interfaces	✅	🔧
@typescript-eslint/no-explicit-any	Disallow usage of the any type	✅	🔧
@typescript-eslint/no-extra-non-null-assertion	Disallow extra non-null assertion	✅	🔧
@typescript-eslint/no-extraneous-class	Forbids the use of classes as namespaces
@typescript-eslint/no-floating-promises	Requires Promise-like values to be handled appropriately	✅		💭
@typescript-eslint/no-for-in-array	Disallow iterating over an array with a for-in loop	✅		💭
@typescript-eslint/no-implicit-any-catch	Disallow usage of the implicit any type in catch clauses		🔧
@typescript-eslint/no-inferrable-types	Disallows explicit type declarations for variables or parameters initialized to a number, string, or boolean	✅	🔧
@typescript-eslint/no-invalid-void-type	Disallows usage of void type outside of generic or return types
@typescript-eslint/no-misused-new	Enforce valid definition of new and constructor	✅
@typescript-eslint/no-misused-promises	Avoid using promises in places not designed to handle them	✅		💭
@typescript-eslint/no-namespace	Disallow the use of custom TypeScript modules and namespaces	✅
@typescript-eslint/no-non-null-asserted-optional-chain	Disallows using a non-null assertion after an optional chain expression	✅
@typescript-eslint/no-non-null-assertion	Disallows non-null assertions using the ! postfix operator	✅
@typescript-eslint/no-parameter-properties	Disallow the use of parameter properties in class constructors
@typescript-eslint/no-require-imports	Disallows invocation of require()
@typescript-eslint/no-this-alias	Disallow aliasing this	✅
@typescript-eslint/no-type-alias	Disallow the use of type aliases
@typescript-eslint/no-unnecessary-boolean-literal-compare	Flags unnecessary equality comparisons against boolean literals		🔧	💭
@typescript-eslint/no-unnecessary-condition	Prevents conditionals where the type is always truthy or always falsy		🔧	💭
@typescript-eslint/no-unnecessary-qualifier	Warns when a namespace qualifier is unnecessary		🔧	💭
@typescript-eslint/no-unnecessary-type-arguments	Enforces that type arguments will not be used if not required		🔧	💭
@typescript-eslint/no-unnecessary-type-assertion	Warns if a type assertion does not change the type of an expression	✅	🔧	💭
@typescript-eslint/no-unnecessary-type-constraint	Disallows unnecessary constraints on generic types		🔧
@typescript-eslint/no-unsafe-argument	Disallows calling an function with an any type value			💭
@typescript-eslint/no-unsafe-assignment	Disallows assigning any to variables and properties	✅		💭
@typescript-eslint/no-unsafe-call	Disallows calling an any type value	✅		💭
@typescript-eslint/no-unsafe-member-access	Disallows member access on any typed variables	✅		💭
@typescript-eslint/no-unsafe-return	Disallows returning any from a function	✅		💭
@typescript-eslint/no-var-requires	Disallows the use of require statements except in import statements	✅
@typescript-eslint/non-nullable-type-assertion-style	Prefers a non-null assertion over explicit type cast when possible		🔧	💭
@typescript-eslint/prefer-as-const	Prefer usage of as const over literal type	✅	🔧
@typescript-eslint/prefer-enum-initializers	Prefer initializing each enums member value
@typescript-eslint/prefer-for-of	Prefer a ‘for-of’ loop over a standard ‘for’ loop if the index is only used to access the array being iterated
@typescript-eslint/prefer-function-type	Use 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 that all enum members be literal values to prevent unintended enum member name shadow issues
@typescript-eslint/prefer-namespace-keyword	Require the use of the namespace keyword instead of the module keyword to declare custom TypeScript modules	✅	🔧
@typescript-eslint/prefer-nullish-coalescing	Enforce the usage of the nullish coalescing operator instead of logical chaining			💭
@typescript-eslint/prefer-optional-chain	Prefer using concise optional chain expressions instead of chained logical ands
@typescript-eslint/prefer-readonly	Requires that private members are marked as readonly if they're never modified outside of the constructor		🔧	💭
@typescript-eslint/prefer-readonly-parameter-types	Requires that function parameters are typed as readonly to prevent accidental mutation of inputs			💭
@typescript-eslint/prefer-reduce-type-parameter	Prefer using type parameter when calling Array#reduce instead of casting		🔧	💭
@typescript-eslint/prefer-regexp-exec	Enforce that RegExp#exec is used instead of String#match if no global flag is provided	✅	🔧	💭
@typescript-eslint/prefer-string-starts-ends-with	Enforce the use of String#startsWith and String#endsWith instead of other equivalent methods of checking substrings		🔧	💭
@typescript-eslint/prefer-ts-expect-error	Recommends using @ts-expect-error over @ts-ignore		🔧
@typescript-eslint/promise-function-async	Requires any function or method that returns a Promise to be marked async		🔧	💭
@typescript-eslint/require-array-sort-compare	Requires Array#sort calls to always provide a compareFunction			💭
@typescript-eslint/restrict-plus-operands	When adding two variables, operands must both be of type number or of type string	✅		💭
@typescript-eslint/restrict-template-expressions	Enforce template literal expressions to be of string type	✅		💭
@typescript-eslint/sort-type-union-intersection-members	Enforces that members of a type union/intersection are sorted alphabetically		🔧
@typescript-eslint/strict-boolean-expressions	Restricts the types allowed in boolean expressions		🔧	💭
@typescript-eslint/switch-exhaustiveness-check	Exhaustiveness checking in switch with union type			💭
@typescript-eslint/triple-slash-reference	Sets preference level for triple slash directives versus ES6-style import declarations	✅
@typescript-eslint/type-annotation-spacing	Require consistent spacing around type annotations		🔧
@typescript-eslint/typedef	Requires type annotations to exist
@typescript-eslint/unbound-method	Enforces unbound methods are called with their expected scope	✅		💭
@typescript-eslint/unified-signatures	Warns for any two overloads that could be unified into one by using 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, 🔧 = fixable, 💭 = requires type information

Name	Description	✅	🔧	💭
@typescript-eslint/brace-style	Enforce consistent brace style for blocks		🔧
@typescript-eslint/comma-dangle	Require or disallow trailing comma		🔧
@typescript-eslint/comma-spacing	Enforces 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-duplicate-imports	Disallow duplicate imports
@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-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/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	Enforces consistent returning of awaited values		🔧	💭
@typescript-eslint/semi	Require or disallow semicolons instead of ASI		🔧
@typescript-eslint/space-before-function-paren	Enforces consistent spacing before function parenthesis		🔧
@typescript-eslint/space-infix-ops	This rule is aimed at ensuring there are spaces around infix operators.		🔧

Contributing

See the contributing guide here.