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node_modules/@typescript-eslint/eslint-plugin/README.md

Getting Started

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, then install the plugin:

yarn add -D @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. 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).

You can read more about linting with type information here

Supported Rules

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

NameDescription:heavy_check_mark::wrench::thought_balloon:
@typescript-eslint/adjacent-overload-signaturesRequire that member overloads be consecutive:heavy_check_mark:
@typescript-eslint/array-typeRequires using either T[] or Array<T> for arrays:wrench:
@typescript-eslint/await-thenableDisallows awaiting a value that is not a Thenable:heavy_check_mark::thought_balloon:
@typescript-eslint/ban-ts-commentBans // @ts-<directive> comments from being used
@typescript-eslint/ban-typesBans specific types from being used:heavy_check_mark::wrench:
@typescript-eslint/consistent-type-assertionsEnforces consistent usage of type assertions:heavy_check_mark:
@typescript-eslint/consistent-type-definitionsConsistent with type definition either interface or type:wrench:
@typescript-eslint/explicit-function-return-typeRequire explicit return types on functions and class methods:heavy_check_mark:
@typescript-eslint/explicit-member-accessibilityRequire explicit accessibility modifiers on class properties and methods:wrench:
@typescript-eslint/explicit-module-boundary-typesRequire explicit return and argument types on exported functions' and classes' public class methods
@typescript-eslint/member-delimiter-styleRequire a specific member delimiter style for interfaces and type literals:heavy_check_mark::wrench:
@typescript-eslint/member-orderingRequire a consistent member declaration order
@typescript-eslint/naming-conventionEnforces naming conventions for everything across a codebase:thought_balloon:
@typescript-eslint/no-base-to-stringRequires that .toString() is only called on objects which provide useful information when stringified:thought_balloon:
@typescript-eslint/no-dynamic-deleteDisallow the delete operator with computed key expressions:wrench:
@typescript-eslint/no-empty-interfaceDisallow the declaration of empty interfaces:heavy_check_mark::wrench:
@typescript-eslint/no-explicit-anyDisallow usage of the any type:heavy_check_mark::wrench:
@typescript-eslint/no-extra-non-null-assertionDisallow extra non-null assertion:wrench:
@typescript-eslint/no-extraneous-classForbids the use of classes as namespaces
@typescript-eslint/no-floating-promisesRequires Promise-like values to be handled appropriately:thought_balloon:
@typescript-eslint/no-for-in-arrayDisallow iterating over an array with a for-in loop:heavy_check_mark::thought_balloon:
@typescript-eslint/no-implied-evalDisallow the use of eval()-like methods:thought_balloon:
@typescript-eslint/no-inferrable-typesDisallows explicit type declarations for variables or parameters initialized to a number, string, or boolean:heavy_check_mark::wrench:
@typescript-eslint/no-misused-newEnforce valid definition of new and constructor:heavy_check_mark:
@typescript-eslint/no-misused-promisesAvoid using promises in places not designed to handle them:heavy_check_mark::thought_balloon:
@typescript-eslint/no-namespaceDisallow the use of custom TypeScript modules and namespaces:heavy_check_mark:
@typescript-eslint/no-non-null-asserted-optional-chainDisallows using a non-null assertion after an optional chain expression
@typescript-eslint/no-non-null-assertionDisallows non-null assertions using the ! postfix operator:heavy_check_mark:
@typescript-eslint/no-parameter-propertiesDisallow the use of parameter properties in class constructors
@typescript-eslint/no-require-importsDisallows invocation of require()
@typescript-eslint/no-this-aliasDisallow aliasing this:heavy_check_mark:
@typescript-eslint/no-throw-literalDisallow throwing literals as exceptions:thought_balloon:
@typescript-eslint/no-type-aliasDisallow the use of type aliases
@typescript-eslint/no-unnecessary-boolean-literal-compareFlags unnecessary equality comparisons against boolean literals:wrench::thought_balloon:
@typescript-eslint/no-unnecessary-conditionPrevents conditionals where the type is always truthy or always falsy:wrench::thought_balloon:
@typescript-eslint/no-unnecessary-qualifierWarns when a namespace qualifier is unnecessary:wrench::thought_balloon:
@typescript-eslint/no-unnecessary-type-argumentsEnforces that type arguments will not be used if not required:wrench::thought_balloon:
@typescript-eslint/no-unnecessary-type-assertionWarns if a type assertion does not change the type of an expression:heavy_check_mark::wrench::thought_balloon:
@typescript-eslint/no-unused-vars-experimentalDisallow unused variables and arguments:thought_balloon:
@typescript-eslint/no-var-requiresDisallows the use of require statements except in import statements:heavy_check_mark:
@typescript-eslint/prefer-as-constPrefer usage of as const over literal type:wrench:
@typescript-eslint/prefer-for-ofPrefer 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-typeUse function types instead of interfaces with call signatures:wrench:
@typescript-eslint/prefer-includesEnforce includes method over indexOf method:heavy_check_mark::wrench::thought_balloon:
@typescript-eslint/prefer-namespace-keywordRequire the use of the namespace keyword instead of the module keyword to declare custom TypeScript modules:heavy_check_mark::wrench:
@typescript-eslint/prefer-nullish-coalescingEnforce the usage of the nullish coalescing operator instead of logical chaining:wrench::thought_balloon:
@typescript-eslint/prefer-optional-chainPrefer using concise optional chain expressions instead of chained logical ands:wrench:
@typescript-eslint/prefer-readonlyRequires that private members are marked as readonly if they're never modified outside of the constructor:wrench::thought_balloon:
@typescript-eslint/prefer-readonly-parameter-typesRequires that function parameters are typed as readonly to prevent accidental mutation of inputs:thought_balloon:
@typescript-eslint/prefer-regexp-execEnforce that RegExp#exec is used instead of String#match if no global flag is provided:heavy_check_mark::thought_balloon:
@typescript-eslint/prefer-string-starts-ends-withEnforce 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-asyncRequires any function or method that returns a Promise to be marked async:thought_balloon:
@typescript-eslint/require-array-sort-compareRequires Array#sort calls to always provide a compareFunction:thought_balloon:
@typescript-eslint/restrict-plus-operandsWhen adding two variables, operands must both be of type number or of type string:thought_balloon:
@typescript-eslint/restrict-template-expressionsEnforce template literal expressions to be of string type:thought_balloon:
@typescript-eslint/strict-boolean-expressionsRestricts the types allowed in boolean expressions:thought_balloon:
@typescript-eslint/switch-exhaustiveness-checkExhaustiveness checking in switch with union type:thought_balloon:
@typescript-eslint/triple-slash-referenceSets preference level for triple slash directives versus ES6-style import declarations:heavy_check_mark:
@typescript-eslint/type-annotation-spacingRequire consistent spacing around type annotations:heavy_check_mark::wrench:
@typescript-eslint/typedefRequires type annotations to exist
@typescript-eslint/unbound-methodEnforces unbound methods are called with their expected scope:heavy_check_mark::thought_balloon:
@typescript-eslint/unified-signaturesWarns 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: :heavy_check_mark: = recommended, :wrench: = fixable, :thought_balloon: = requires type information

NameDescription:heavy_check_mark::wrench::thought_balloon:
@typescript-eslint/brace-styleEnforce consistent brace style for blocks:wrench:
@typescript-eslint/comma-spacingEnforces consistent spacing before and after commas:wrench:
@typescript-eslint/default-param-lastEnforce default parameters to be last
@typescript-eslint/func-call-spacingRequire or disallow spacing between function identifiers and their invocations:wrench:
@typescript-eslint/indentEnforce consistent indentation:wrench:
@typescript-eslint/no-array-constructorDisallow generic Array constructors:heavy_check_mark::wrench:
@typescript-eslint/no-dupe-class-membersDisallow duplicate class members
@typescript-eslint/no-empty-functionDisallow empty functions:heavy_check_mark:
@typescript-eslint/no-extra-parensDisallow unnecessary parentheses:wrench:
@typescript-eslint/no-extra-semiDisallow unnecessary semicolons:wrench:
@typescript-eslint/no-magic-numbersDisallow magic numbers
@typescript-eslint/no-unused-expressionsDisallow unused expressions
@typescript-eslint/no-unused-varsDisallow unused variables:heavy_check_mark:
@typescript-eslint/no-use-before-defineDisallow the use of variables before they are defined:heavy_check_mark:
@typescript-eslint/no-useless-constructorDisallow unnecessary constructors
@typescript-eslint/quotesEnforce the consistent use of either backticks, double, or single quotes:wrench:
@typescript-eslint/require-awaitDisallow async functions which have no await expression:heavy_check_mark::thought_balloon:
@typescript-eslint/return-awaitEnforces consistent returning of awaited values:wrench::thought_balloon:
@typescript-eslint/semiRequire or disallow semicolons instead of ASI:wrench:
@typescript-eslint/space-before-function-parenEnforces consistent spacing before function parenthesis:wrench:

Contributing

See the contributing guide here.