@typescript-eslint/eslint-plugin

What is @typescript-eslint/eslint-plugin?

The @typescript-eslint/eslint-plugin package is an ESLint plugin that contains a set of ESLint rules that are specifically designed for TypeScript code. It helps in identifying and reporting on patterns found in TypeScript code, and it can be used to enforce a wide range of coding standards and conventions.

What are @typescript-eslint/eslint-plugin's main functionalities?

Type-aware linting

This feature allows for rules that require type information. For example, the 'strict-boolean-expressions' rule ensures that boolean expressions are clear and error-free by considering the types involved in the expression.

/* eslint @typescript-eslint/strict-boolean-expressions: 'error' */
function isTruthy(value: any): boolean {
  return Boolean(value);
}

Code style enforcement

Enforces naming conventions for everything from variables to type parameters. This example enforces camelCase naming for variables.

/* eslint @typescript-eslint/naming-convention: ['error', { 'selector': 'variable', 'format': ['camelCase'] }] */
let myVariable = 1;

Accessibility checks

This feature requires functions and methods to explicitly define their return type to improve code readability and maintainability.

/* eslint @typescript-eslint/explicit-function-return-type: 'warn' */
function add(x: number, y: number) {
  return x + y;
}

Other packages similar to @typescript-eslint/eslint-plugin

eslint-plugin-react

This package provides linting rules for React and JSX. It's similar to @typescript-eslint/eslint-plugin in that it extends ESLint's capabilities to a specific language extension, but it focuses on React rather than TypeScript.

eslint-plugin-vue

This package is designed for linting Vue.js templates and scripts. Like @typescript-eslint/eslint-plugin, it provides additional rules that are specific to the Vue.js framework, complementing the standard ESLint rules.

eslint-plugin-import

This plugin provides a set of rules that help ensure proper imports, exports, and module structure. While it's not specific to TypeScript, it complements @typescript-eslint/eslint-plugin by enforcing best practices in module usage.

README

ESLint Plugin TypeScript

Installation

Make sure you have TypeScript and @typescript-eslint/parser installed, then install the plugin:

npm i @typescript-eslint/eslint-plugin --save-dev

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:

{
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"]
}

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"]
}

You can also use eslint:recommended (the set of rules which are recommended for all projects by the ESLint Team) with this plugin. As noted in the root README, not all eslint core rules are compatible with TypeScript, so you need to add both eslint:recommended and plugin:@typescript-eslint/eslint-recommended (which will adjust the one from eslint appropriately for TypeScript) to your config:

{
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/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/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).

NOTE: If you want to use rules which require type information, you will need to specify a path to your tsconfig.json file in the "project" property of "parserOptions". If you do not do this, you will get a runtime error which explains this.

{
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "project": "./tsconfig.json"
  },
  "plugins": ["@typescript-eslint"],
  "rules": {
    "@typescript-eslint/restrict-plus-operands": "error"
  }
}

See @typescript-eslint/parser's README.md for more information on the available "parserOptions".

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

Usage with Prettier

Install eslint-config-prettier to disable our code formatting related rules:

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

Note: Make sure you have eslint-config-prettier@4.0.0 or newer.

Usage with Airbnb

Airbnb has two configs, a base one eslint-config-airbnb-base and one that includes rules for React eslint-config-airbnb.

First you'll need to install the config according to the instructions in one of the links above. npx install-peerdeps --dev eslint-config-airbnb or npx install-peerdeps --dev eslint-config-airbnb-base should work if you are using npm 5+.

Then you should add airbnb (or airbnb-base) to your extends section of .eslintrc. You might also want to turn on plugin:@typescript-eslint/recommended as well to enable all of the recommended rules.

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

Note: You can use Airbnb's rules alongside Prettier, see Usage with Prettier

Supported Rules

Key: :heavy_check_mark: = recommended, :wrench: = fixable, :thought_balloon: = requires type information

Name	Description	:heavy_check_mark:	:wrench:	:thought_balloon:
@typescript-eslint/adjacent-overload-signatures	Require that member overloads be consecutive	:heavy_check_mark:
@typescript-eslint/array-type	Requires using either T[] or Array<T> for arrays		:wrench:
@typescript-eslint/await-thenable	Disallows awaiting a value that is not a Thenable	:heavy_check_mark:		:thought_balloon:
@typescript-eslint/ban-ts-ignore	Bans “// @ts-ignore” comments from being used	:heavy_check_mark:
@typescript-eslint/ban-types	Bans specific types from being used	:heavy_check_mark:	:wrench:
@typescript-eslint/brace-style	Enforce consistent brace style for blocks		:wrench:
@typescript-eslint/camelcase	Enforce camelCase naming convention	:heavy_check_mark:
@typescript-eslint/class-name-casing	Require PascalCased class and interface names	:heavy_check_mark:
@typescript-eslint/consistent-type-assertions	Enforces consistent usage of type assertions.	:heavy_check_mark:
@typescript-eslint/consistent-type-definitions	Consistent with type definition either interface or type		:wrench:
@typescript-eslint/explicit-function-return-type	Require explicit return types on functions and class methods	:heavy_check_mark:
@typescript-eslint/explicit-member-accessibility	Require explicit accessibility modifiers on class properties and methods
@typescript-eslint/func-call-spacing	Require or disallow spacing between function identifiers and their invocations		:wrench:
@typescript-eslint/generic-type-naming	Enforces naming of generic type variables
@typescript-eslint/indent	Enforce consistent indentation		:wrench:
@typescript-eslint/interface-name-prefix	Require that interface names should or should not prefixed with I	:heavy_check_mark:
@typescript-eslint/member-delimiter-style	Require a specific member delimiter style for interfaces and type literals	:heavy_check_mark:	:wrench:
@typescript-eslint/member-naming	Enforces naming conventions for class members by visibility
@typescript-eslint/member-ordering	Require a consistent member declaration order
@typescript-eslint/no-array-constructor	Disallow generic Array constructors	:heavy_check_mark:	:wrench:
@typescript-eslint/no-empty-function	Disallow empty functions	:heavy_check_mark:
@typescript-eslint/no-empty-interface	Disallow the declaration of empty interfaces	:heavy_check_mark:
@typescript-eslint/no-explicit-any	Disallow usage of the any type	:heavy_check_mark:	:wrench:
@typescript-eslint/no-extra-parens	Disallow unnecessary parentheses		:wrench:
@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.			:thought_balloon:
@typescript-eslint/no-for-in-array	Disallow iterating over an array with a for-in loop	:heavy_check_mark:		:thought_balloon:
@typescript-eslint/no-inferrable-types	Disallows explicit type declarations for variables or parameters initialized to a number, string, or boolean	:heavy_check_mark:	:wrench:
@typescript-eslint/no-magic-numbers	Disallows magic numbers
@typescript-eslint/no-misused-new	Enforce valid definition of new and constructor	:heavy_check_mark:
@typescript-eslint/no-misused-promises	Avoid using promises in places not designed to handle them	:heavy_check_mark:		:thought_balloon:
@typescript-eslint/no-namespace	Disallow the use of custom TypeScript modules and namespaces	:heavy_check_mark:
@typescript-eslint/no-non-null-assertion	Disallows non-null assertions using the ! postfix operator	:heavy_check_mark:
@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	:heavy_check_mark:
@typescript-eslint/no-type-alias	Disallow the use of type aliases
@typescript-eslint/no-unnecessary-condition	Prevents conditionals where the type is always truthy or always falsy			:thought_balloon:
@typescript-eslint/no-unnecessary-qualifier	Warns when a namespace qualifier is unnecessary		:wrench:	:thought_balloon:
@typescript-eslint/no-unnecessary-type-arguments	Warns if an explicitly specified type argument is the default for that type parameter		:wrench:	:thought_balloon:
@typescript-eslint/no-unnecessary-type-assertion	Warns if a type assertion does not change the type of an expression	:heavy_check_mark:	:wrench:	:thought_balloon:
@typescript-eslint/no-unused-vars	Disallow unused variables	:heavy_check_mark:
@typescript-eslint/no-use-before-define	Disallow the use of variables before they are defined	:heavy_check_mark:
@typescript-eslint/no-useless-constructor	Disallow unnecessary constructors
@typescript-eslint/no-var-requires	Disallows the use of require statements except in import statements	:heavy_check_mark:
@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		:wrench:
@typescript-eslint/prefer-includes	Enforce includes method over indexOf method	:heavy_check_mark:	:wrench:	:thought_balloon:
@typescript-eslint/prefer-namespace-keyword	Require the use of the namespace keyword instead of the module keyword to declare custom TypeScript modules	:heavy_check_mark:	:wrench:
@typescript-eslint/prefer-readonly	Requires that private members are marked as readonly if they're never modified outside of the constructor		:wrench:	:thought_balloon:
@typescript-eslint/prefer-regexp-exec	Prefer RegExp#exec() over String#match() if no global flag is provided	:heavy_check_mark:		:thought_balloon:
@typescript-eslint/prefer-string-starts-ends-with	Enforce the use of String#startsWith and String#endsWith instead of other equivalent methods of checking substrings	:heavy_check_mark:	:wrench:	:thought_balloon:
@typescript-eslint/promise-function-async	Requires any function or method that returns a Promise to be marked async			:thought_balloon:
@typescript-eslint/quotes	Enforce the consistent use of either backticks, double, or single quotes		:wrench:
@typescript-eslint/require-array-sort-compare	Enforce giving compare argument to Array#sort			:thought_balloon:
@typescript-eslint/require-await	Disallow async functions which have no await expression	:heavy_check_mark:		:thought_balloon:
@typescript-eslint/restrict-plus-operands	When adding two variables, operands must both be of type number or of type string			:thought_balloon:
@typescript-eslint/semi	Require or disallow semicolons instead of ASI		:wrench:
@typescript-eslint/strict-boolean-expressions	Restricts the types allowed in boolean expressions			:thought_balloon:
@typescript-eslint/triple-slash-reference	Sets preference level for triple slash directives versus ES6-style import declarations	:heavy_check_mark:
@typescript-eslint/type-annotation-spacing	Require consistent spacing around type annotations	:heavy_check_mark:	:wrench:
@typescript-eslint/typedef	Requires type annotations to exist
@typescript-eslint/unbound-method	Enforces unbound methods are called with their expected scope	:heavy_check_mark:		:thought_balloon:
@typescript-eslint/unified-signatures	Warns for any two overloads that could be unified into one by using a union or an optional/rest parameter