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eslint-plugin-flowtype
Advanced tools
eslint-plugin-flowtype is an ESLint plugin that provides linting rules for Flow type annotations. It helps ensure that your Flow type annotations are correct and consistent, improving the reliability and maintainability of your code.
Type Annotations
This rule ensures that every file has a valid Flow file annotation. The code sample demonstrates a simple function with Flow type annotations for the parameters and return type.
/* eslint flowtype/require-valid-file-annotation: [2, "always"] */
// @flow
function add(a: number, b: number): number {
return a + b;
}
Type Definitions
This rule ensures that all Flow type definitions are defined correctly. The code sample shows a type definition for a User object and an instance of that type.
/* eslint flowtype/define-flow-type: 2 */
// @flow
type User = {
name: string,
age: number
};
const user: User = { name: 'John', age: 30 };
Type Casting
This rule enforces a naming convention for type identifiers. The code sample demonstrates a type definition that follows the specified naming convention.
/* eslint flowtype/type-id-match: [2, "^([A-Z][a-z0-9]+)+Type$"] */
// @flow
type UserType = {
name: string,
age: number
};
const user: UserType = { name: 'John', age: 30 };
eslint-plugin-typescript is an ESLint plugin that provides linting rules for TypeScript code. It offers similar functionality to eslint-plugin-flowtype but is designed for TypeScript instead of Flow. It helps ensure that your TypeScript code is correct and consistent.
typescript-eslint is a set of tools that allows ESLint to lint TypeScript code. It includes an ESLint plugin and a parser that can handle TypeScript syntax. Like eslint-plugin-flowtype, it helps maintain code quality and consistency, but it is tailored for TypeScript.
Flow type linting rules for ESLint.
babel-eslint
parser (ESLint parser does not support type annotations).eslint-plugin-flowtype
plugin.npm install eslint
npm install babel-eslint
npm install eslint-plugin-flowtype
parser
property to babel-eslint
.plugins
section and specify eslint-plugin-flowtype
as a plugin.{
"parser": "babel-eslint",
"plugins": [
"flowtype"
],
"rules": {
"flowtype/define-flow-type": 1,
"flowtype/require-parameter-type": 1,
"flowtype/require-return-type": [
1,
"always",
{
"annotateUndefined": "never"
}
],
"flowtype/space-after-type-colon": [
1,
"always"
],
"flowtype/space-before-type-colon": [
1,
"never"
],
"flowtype/type-id-match": [
1,
"^([A-Z][a-z0-9]+)+Type$"
],
"flowtype/use-flow-type": 1,
"flowtype/valid-syntax": 1
},
"settings": {
"flowtype": {
"onlyFilesWithFlowAnnotation": false
}
}
}
onlyFilesWithFlowAnnotation
When true
, only checks files with a @flow
annotation in the first comment.
{
"settings": {
"flowtype": {
"onlyFilesWithFlowAnnotation": true
}
}
}
define-flow-type
Marks Flow type identifiers as defined.
Used to suppress no-undef
reporting of type identifiers.
The following patterns are not considered problems:
var a: AType
// Additional rules: {"no-undef":2}
var a: AType; var b: AType
// Additional rules: {"no-undef":2}
var a; (a: AType)
// Additional rules: {"no-undef":2}
var a: AType<BType>
// Additional rules: {"no-undef":2}
type A = AType
// Additional rules: {"no-undef":2}
function f(a: AType) {}
// Additional rules: {"no-undef":2}
function f(a: AType.a) {}
// Additional rules: {"no-undef":2}
function f(a: AType.a.b) {}
// Additional rules: {"no-undef":2}
function f(a): AType {}; var a: AType
// Additional rules: {"no-undef":2}
function f(a): AType {}
// Additional rules: {"no-undef":2}
class C { a: AType }
// Additional rules: {"no-undef":2}
class C { a: AType.a }
// Additional rules: {"no-undef":2}
class C { a: AType.a.b }
// Additional rules: {"no-undef":2}
class C implements AType {}
// Additional rules: {"no-undef":2}
interface AType {}
// Additional rules: {"no-undef":2}
({ a: ({b() {}}: AType) })
// Additional rules: {"no-undef":2}
type X = {Y<AType>(): BType}
// Additional rules: {"no-undef":2}
interface AType<BType> {}
// Additional rules: {"no-undef":2}
var a: AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
var a: AType; var b: AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
var a; (a: AType)
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
var a: AType<BType>
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
type A = AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
function f(a: AType) {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
function f(a: AType.a) {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
function f(a: AType.a.b) {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
function f(a): AType {}; var a: AType
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
function f(a): AType {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
class C { a: AType }
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
class C { a: AType.a }
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
class C { a: AType.a.b }
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
class C implements AType {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
interface AType {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
({ a: ({b() {}}: AType) })
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
type X = {Y<AType>(): BType}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
interface AType<BType> {}
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
require-parameter-type
Requires that all function parameters have type annotations.
You can skip all arrow functions by providing the excludeArrowFunctions
option with true
.
Alternatively, you can want to exclude only function expressions (e.g. x => x * 2
). Provide excludeArrowFunctions
with expressionsOnly
for this.
{
"rules": {
"flowtype/require-parameter-type": [
2,
{
"excludeArrowFunctions": true
}
]
}
}
{
"rules": {
"flowtype/require-parameter-type": [
2,
{
"excludeArrowFunctions": "expressionsOnly"
}
]
}
}
The following patterns are considered problems:
(foo) => {}
// Message: Missing "foo" parameter type annotation.
function x(foo) {}
// Message: Missing "foo" parameter type annotation.
// Options: [{"excludeArrowFunctions":true}]
function x(foo) {}
// Message: Missing "foo" parameter type annotation.
(foo = 'FOO') => {}
// Message: Missing "foo" parameter type annotation.
(...foo) => {}
// Message: Missing "foo" parameter type annotation.
({foo}) => {}
// Message: Missing "{foo}" parameter type annotation.
([foo]) => {}
// Message: Missing "[foo]" parameter type annotation.
({foo = 1} = {}) => {}
// Message: Missing "{foo = 1}" parameter type annotation.
// @flow
(foo) => {}
// Message: Missing "foo" parameter type annotation.
// Options: [{"excludeArrowFunctions":"expressionsOnly"}]
(foo) => {}
// Message: Missing "foo" parameter type annotation.
// Options: [{"excludeArrowFunctions":"expressionsOnly"}]
function x(foo) {}
// Message: Missing "foo" parameter type annotation.
The following patterns are not considered problems:
(foo: string) => {}
(foo: string = 'FOO') => {}
(...foo: string) => {}
({foo}: {foo: string}) => {}
([foo]: Array) => {}
(foo) => {}
// Options: [{"excludeArrowFunctions":true}]
(foo) => {}
// Options: [{"excludeArrowFunctions":"expressionsOnly"}]
(foo) => 3
require-return-type
Requires that functions have return type annotation.
You can skip all arrow functions by providing the excludeArrowFunctions
option with true
.
Alternatively, you can want to exclude only function expressions (e.g. () => 2
). Provide excludeArrowFunctions
with expressionsOnly
for this.
{
"rules": {
"flowtype/require-return-type": [
2,
"always",
{
"excludeArrowFunctions": true
}
]
}
}
{
"rules": {
"flowtype/require-return-type": [
2,
"always",
{
"excludeArrowFunctions": "expressionsOnly"
}
]
}
}
The following patterns are considered problems:
(foo) => { return "foo"; }
// Message: Missing return type annotation.
// Options: ["always"]
(foo) => { return "foo"; }
// Message: Missing return type annotation.
// Options: ["always"]
(foo) => "foo"
// Message: Missing return type annotation.
(foo) => ({})
// Message: Missing return type annotation.
(foo): undefined => { return; }
// Message: Must not annotate undefined return type.
(foo): void => { return; }
// Message: Must not annotate undefined return type.
(foo): undefined => { return undefined; }
// Message: Must not annotate undefined return type.
(foo): void => { return void 0; }
// Message: Must not annotate undefined return type.
// Options: ["always",{"annotateUndefined":"never"}]
(foo): undefined => { return; }
// Message: Must not annotate undefined return type.
// Options: ["always",{"annotateUndefined":"never"}]
(foo): void => { return; }
// Message: Must not annotate undefined return type.
// Options: ["always",{"annotateUndefined":"always"}]
(foo) => { return; }
// Message: Must annotate undefined return type.
// Options: ["always",{"annotateUndefined":"never"}]
(foo): undefined => { return undefined; }
// Message: Must not annotate undefined return type.
// Options: ["always",{"annotateUndefined":"always"}]
(foo) => { return undefined; }
// Message: Must annotate undefined return type.
// Options: ["always",{"annotateUndefined":"always"}]
(foo) => { return void 0; }
// Message: Must annotate undefined return type.
// @flow
(foo) => { return 1; }
// Message: Missing return type annotation.
// Options: ["always",{"annotateUndefined":"always"}]
// @flow
(foo) => { return undefined; }
// Message: Must annotate undefined return type.
// Options: ["always"]
async () => { return 2; }
// Message: Missing return type annotation.
// Options: ["always",{"annotateUndefined":"always"}]
async () => {}
// Message: Missing return type annotation.
// Options: ["always",{"annotateUndefined":"always"}]
async function x() {}
// Message: Missing return type annotation.
// Options: ["always"]
async () => { return; }
// Message: Missing return type annotation.
// Options: ["always"]
function* x() {}
// Message: Missing return type annotation.
// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
() => { return 3; }
// Message: Missing return type annotation.
// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
async () => { return 4; }
// Message: Missing return type annotation.
The following patterns are not considered problems:
(foo): string => {}
// Options: ["always"]
(foo): string => {}
(foo) => { return; }
(foo): Object => ( {} )
(foo) => { return undefined; }
(foo) => { return void 0; }
// Options: ["always",{"annotateUndefined":"always"}]
(foo): undefined => { return; }
// Options: ["always",{"annotateUndefined":"always"}]
(foo): void => { return; }
// Options: ["always",{"annotateUndefined":"never"}]
(foo) => { return; }
// Options: ["always",{"annotateUndefined":"never"}]
(foo) => { return undefined; }
// Options: ["always",{"annotateUndefined":"never"}]
(foo) => { return void 0; }
// Options: ["always",{"annotateUndefined":"always"}]
(foo): undefined => { return undefined; }
// Options: ["always",{"annotateUndefined":"always"}]
(foo): void => { return void 0; }
// Options: ["always"]
(foo) => { return 1; }
// Options: ["always",{"annotateUndefined":"always"}]
(foo) => { return undefined; }
// Options: ["always",{"annotateUndefined":"always"}]
async function doThing(): Promise<void> {}
// Options: ["always",{"annotateUndefined":"always"}]
function* doThing(): Generator<number, void, void> { yield 2; }
async (foo): Promise<number> => { return 3; }
// Options: ["always",{"excludeArrowFunctions":true}]
() => 3
// Options: ["always",{"excludeArrowFunctions":true}]
() => { return 4; }
// Options: ["always",{"excludeArrowFunctions":true}]
() => undefined
// Options: ["always",{"annotateUndefined":"always","excludeArrowFunctions":true}]
() => undefined
// Options: ["always",{"annotateUndefined":"always","excludeArrowFunctions":true}]
() => { return undefined; }
// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
() => 3
// Options: ["always",{"excludeArrowFunctions":"expressionsOnly"}]
async () => 3
require-valid-file-annotation
Makes sure that files have a valid @flow
annotation. It will report annotations with typos (such as // @floww
) or not placed at the top of the file, and optionaly missing annotations.
By default, this rule won't complain if there is no @flow
annotation at all in the file. Passing a "always"
option reports files missing those annotations as well.
{
"rules": {
"flowtype/require-valid-file-annotation": [
2,
"always"
]
}
}
The following patterns are considered problems:
;// @flow
// Message: Flow file annotation not at the top of the file.
;
// @flow
// Message: Flow file annotation not at the top of the file.
// @Flow
// Message: Malformed flow file annotation.
// @floweeeeeee
// Message: Malformed flow file annotation.
// Options: ["always"]
a;
// Message: Flow file annotation is missing.
The following patterns are not considered problems:
a;
// @flow
a;
//@flow
a;
//**@flow
a;
/* foo @flow bar */
a;
// @flow
a;
// @flow
// @FLow
// Options: ["always"]
a;
space-after-type-colon
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces consistent spacing after the type annotation colon.
This rule takes one argument. If it is 'always'
then a problem is raised when there is no space after the type annotation colon. If it is 'never'
then a problem is raised when there is a space after the type annotation colon. The default value is 'always'
.
The following patterns are considered problems:
// Options: ["never"]
(foo: string) => {}
// Message: There must be no space after "foo" parameter type annotation colon.
// Options: ["never"]
export default function (foo: string) {}
// Message: There must be no space after "foo" parameter type annotation colon.
// Options: ["never"]
function foo (foo: string) {}
// Message: There must be no space after "foo" parameter type annotation colon.
// Options: ["always"]
(foo:string) => {}
// Message: There must be a space after "foo" parameter type annotation colon.
function foo (foo:string) {}
// Message: There must be a space after "foo" parameter type annotation colon.
// Options: ["always"]
(foo: string) => {}
// Message: There must be 1 space after "foo" parameter type annotation colon.
// Options: ["always"]
(foo:(() => void)) => {}
// Message: There must be a space after "foo" parameter type annotation colon.
// Options: ["never"]
(foo: (() => void)) => {}
// Message: There must be no space after "foo" parameter type annotation colon.
// Options: ["always"]
(foo: (() => void)) => {}
// Message: There must be 1 space after "foo" parameter type annotation colon.
// Options: ["always"]
():Object => {}
// Message: There must be a space after return type colon.
// Options: ["never"]
(): Object => {}
// Message: There must be no space after return type colon.
// Options: ["always"]
(): Object => {}
// Message: There must be 1 space after return type colon.
// Options: ["always"]
():(() => void) => {}
// Message: There must be a space after return type colon.
// Options: ["never"]
(): (() => void) => {}
// Message: There must be no space after return type colon.
// Options: ["always"]
(): (() => void) => {}
// Message: There must be 1 space after return type colon.
async function foo({ lorem, ipsum, dolor }:SomeType) {}
// Message: There must be a space after "{ lorem, ipsum, dolor }:SomeType" parameter type annotation colon.
({ lorem, ipsum, dolor } : SomeType) => {}
// Message: There must be 1 space after "{ lorem, ipsum, dolor }" parameter type annotation colon.
(foo:{ a: string, b: number }) => {}
// Message: There must be a space after "foo" parameter type annotation colon.
({ a, b } :{ a: string, b: number }) => {}
// Message: There must be a space after "{ a, b }" parameter type annotation colon.
([ a, b ] :string[]) => {}
// Message: There must be a space after "[ a, b ]" parameter type annotation colon.
type X = { foo:string }
// Message: There must be a space after "foo" type annotation colon.
// Options: ["always"]
type X = { foo:string }
// Message: There must be a space after "foo" type annotation colon.
// Options: ["never"]
type X = { foo: string }
// Message: There must be no space after "foo" type annotation colon.
type X = { foo: string }
// Message: There must be 1 space after "foo" type annotation colon.
type X = { foo?:string }
// Message: There must be a space after "foo" type annotation colon.
// Options: ["never"]
type X = { foo?: string }
// Message: There must be no space after "foo" type annotation colon.
type X = { foo?:?string }
// Message: There must be a space after "foo" type annotation colon.
type X = { foo?: ?string }
// Message: There must be 1 space after "foo" type annotation colon.
class X { foo:string }
// Message: There must be a space after "foo" class property type annotation colon.
// Options: ["never"]
class X { foo: string }
// Message: There must be no space after "foo" class property type annotation colon.
class X { foo:?string }
// Message: There must be a space after "foo" class property type annotation colon.
// Options: ["never"]
class X { foo: ?string }
// Message: There must be no space after "foo" class property type annotation colon.
type X = (foo:number) => string
// Message: There must be a space after "foo" parameter type annotation colon.
// Options: ["never"]
type X = (foo: number) => string
// Message: There must be no space after "foo" parameter type annotation colon.
type X = (foo: number) => string
// Message: There must be 1 space after "foo" parameter type annotation colon.
type X = (foo:?number) => string
// Message: There must be a space after "foo" parameter type annotation colon.
The following patterns are not considered problems:
(foo) => {}
(foo: string) => {}
function x(foo: string) {}
class Foo { constructor(foo: string) {} }
(foo: (string|number)) => {}
// Options: ["never"]
(foo:string) => {}
// Options: ["never"]
function x(foo:string) {}
// Options: ["never"]
class Foo { constructor(foo:string) {} }
// Options: ["always"]
(foo: string) => {}
// Options: ["never"]
(foo:(() => void)) => {}
// Options: ["always"]
(foo: (() => void)) => {}
// Options: ["never"]
():Object => {}
// Options: ["always"]
(): Object => {}
// Options: ["never"]
():(number | string) => {}
// Options: ["always"]
(): (number | string) => {}
// Options: ["never"]
():number|string => {}
// Options: ["always"]
(): number|string => {}
// Options: ["never"]
():(() => void) => {}
// Options: ["always"]
(): (() => void) => {}
// Options: ["never"]
():( () => void ) => {}
// Options: ["always"]
(): ( () => void ) => {}
async function foo({ lorem, ipsum, dolor }: SomeType) {}
({ lorem, ipsum, dolor }: SomeType) => {}
(foo: { a: string, b: number }) => {}
({ a, b }: ?{ a: string, b: number }) => {}
function x({ a, b }: { a: string, b: number }) {}
(): { a: number, b: string } => {}
// Options: ["never"]
() :{ a:number, b:string } => {}
([ a, b ]: string[]) => {}
type X = { foo: string }
// Options: ["never"]
type X = { foo:string }
type X = { foo?: string }
type X = { foo?: ?string }
// Options: ["never"]
type X = { foo?:?string }
class Foo { bar }
class Foo { bar = 3 }
class Foo { bar: string }
class Foo { bar: ?string }
// Options: ["never"]
class Foo { bar:string }
// Options: ["never"]
class Foo { bar:?string }
type X = (foo: number) => string;
type X = (foo : number) => string;
type X = (foo: ?number) => string;
type X = (foo? : ?number) => string;
type X = (foo: ?{ x: number }) => string;
// Options: ["never"]
type X = (foo:number) => string;
// Options: ["never"]
type X = (foo:?{ x:number }) => string;
space-before-type-colon
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces consistent spacing before the type annotation colon.
This rule takes one argument. If it is 'always'
then a problem is raised when there is no space before the type annotation colon. If it is 'never'
then a problem is raised when there is a space before the type annotation colon. The default value is 'never'
.
The following patterns are considered problems:
// Options: ["never"]
(foo : string) => {}
// Message: There must be no space before "foo" parameter type annotation colon.
// Options: ["never"]
(foo ? : string) => {}
// Message: There must be no space before "foo" parameter type annotation colon.
// Options: ["always"]
(foo: string) => {}
// Message: There must be a space before "foo" parameter type annotation colon.
// Options: ["always"]
(foo : string) => {}
// Message: There must be 1 space before "foo" parameter type annotation colon.
// Options: ["always"]
(foo?: string) => {}
// Message: There must be a space before "foo" parameter type annotation colon.
// Options: ["always"]
(foo ? : string) => {}
// Message: There must be 1 space before "foo" parameter type annotation colon.
// Options: ["always"]
(foo ?: string) => {}
// Message: There must be a space before "foo" parameter type annotation colon.
function x(foo : string) {}
// Message: There must be no space before "foo" parameter type annotation colon.
// Options: ["always"]
function x(foo: string) {}
// Message: There must be a space before "foo" parameter type annotation colon.
var x = function (foo : string) {}
// Message: There must be no space before "foo" parameter type annotation colon.
// Options: ["always"]
var x = function (foo: string) {}
// Message: There must be a space before "foo" parameter type annotation colon.
class Foo { constructor(foo : string ) {} }
// Message: There must be no space before "foo" parameter type annotation colon.
// Options: ["always"]
class Foo { constructor(foo: string ) {} }
// Message: There must be a space before "foo" parameter type annotation colon.
async function foo({ lorem, ipsum, dolor } : SomeType) {}
// Message: There must be no space before "{ lorem, ipsum, dolor } : SomeType" parameter type annotation colon.
({ lorem, ipsum, dolor } : SomeType) => {}
// Message: There must be no space before "{ lorem, ipsum, dolor }" parameter type annotation colon.
(foo : { a: string, b: number }) => {}
// Message: There must be no space before "foo" parameter type annotation colon.
({ a, b } : { a: string, b: number }) => {}
// Message: There must be no space before "{ a, b }" parameter type annotation colon.
([ a, b ] : string[]) => {}
// Message: There must be no space before "[ a, b ]" parameter type annotation colon.
type X = { foo : string }
// Message: There must be no space before "foo" type annotation colon.
// Options: ["never"]
type X = { foo : string }
// Message: There must be no space before "foo" type annotation colon.
// Options: ["always"]
type X = { foo: string }
// Message: There must be a space before "foo" type annotation colon.
// Options: ["always"]
type X = { foo : string }
// Message: There must be 1 space before "foo" type annotation colon.
type X = { foo? : string }
// Message: There must be no space before "foo" type annotation colon.
// Options: ["always"]
type X = { foo?: string }
// Message: There must be a space before "foo" type annotation colon.
// Options: ["always"]
type X = { foo? : string }
// Message: There must be 1 space before "foo" type annotation colon.
// Options: ["always"]
type X = { foo ?: string }
// Message: There must be a space before "foo" type annotation colon.
class X { foo :string }
// Message: There must be no space before "foo" class property type annotation colon.
// Options: ["always"]
class X { foo: string }
// Message: There must be a space before "foo" class property type annotation colon.
class X { foo :?string }
// Message: There must be no space before "foo" class property type annotation colon.
// Options: ["always"]
class X { foo: ?string }
// Message: There must be a space before "foo" class property type annotation colon.
type X = (foo :string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.
// Options: ["always"]
type X = (foo:string) => string;
// Message: There must be a space before "foo" parameter type annotation colon.
// Options: ["always"]
type X = (foo :string) => string;
// Message: There must be 1 space before "foo" parameter type annotation colon.
type X = (foo? :string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.
type X = (foo? :string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.
// Options: ["always"]
type X = (foo?:string) => string;
// Message: There must be a space before "foo" parameter type annotation colon.
type X = (foo? :?string) => string;
// Message: There must be no space before "foo" parameter type annotation colon.
The following patterns are not considered problems:
(foo) => {}
(foo: string) => {}
(foo?: string) => {}
(foo ?: string) => {}
// Options: ["never"]
(foo: string) => {}
// Options: ["always"]
(foo : string) => {}
// Options: ["always"]
(foo? : string) => {}
// Options: ["always"]
(foo ? : string) => {}
// Options: ["always"]
(foo ? : string) => {}
function x(foo: string) {}
// Options: ["always"]
function x(foo : string) {}
var x = function (foo: string) {}
// Options: ["always"]
var x = function (foo : string) {}
class Foo { constructor(foo: string ) {} }
// Options: ["always"]
class Foo { constructor(foo : string ) {} }
async function foo({ lorem, ipsum, dolor }: SomeType) {}
({ lorem, ipsum, dolor }: SomeType) => {}
(foo: { a: string, b: number }) => {}
({ a, b }: ?{ a: string, b: number }) => {}
function x({ a, b }: { a: string, b: number }) {}
(): { a: number, b: string } => {}
// Options: ["always"]
() : { a : number, b : string } => {}
([ a, b ]: string[]) => {}
type X = { foo: string }
// Options: ["always"]
type X = { foo : string }
type X = { foo?: string }
type X = { foo ?: string }
// Options: ["always"]
type X = { foo? : string }
class Foo { bar }
class Foo { bar = 3 }
class Foo { bar: string }
class Foo { bar: ?string }
class Foo { bar:?string }
// Options: ["always"]
class Foo { bar : string }
type X = (foo:string) => number;
type X = (foo: string) => number;
type X = (foo: ?string) => number;
type X = (foo?: string) => number;
type X = (foo?: ?string) => number;
type X = (foo ?: string) => number;
// Options: ["always"]
type X = (foo? : string) => number
// Options: ["always"]
type X = (foo? : ?string) => number
type-id-match
Enforces a consistent naming pattern for type aliases.
This rule needs a text RegExp to operate with Its signature is as follows:
{
"rules": {
"flowtype/type-id-match": [
2,
"^([A-Z][a-z0-9]+)+Type$"
]
}
}
'^([A-Z][a-z0-9]+)+Type$'
is the default pattern.
The following patterns are considered problems:
type foo = {};
// Message: Type identifier 'foo' does not match pattern '/^([A-Z][a-z0-9]+)+Type$/'.
// Options: ["^foo$"]
type FooType = {};
// Message: Type identifier 'FooType' does not match pattern '/^foo$/'.
The following patterns are not considered problems:
type FooType = {};
// Options: ["^foo$"]
type foo = {};
use-flow-type
Marks Flow type alias declarations as used.
Used to suppress no-unused-vars
errors that are triggered by type aliases.
The following patterns are not considered problems:
declare class A {}
// Additional rules: {"no-unused-vars":1}
declare function A(): Y
// Additional rules: {"no-unused-vars":1}
declare module A {}
// Additional rules: {"no-unused-vars":1}
declare module A { declare var a: Y }
// Additional rules: {"no-unused-vars":1}
declare var A: Y
// Additional rules: {"no-unused-vars":1}
import type A from "a"; (function<T: A>(): T {})
// Additional rules: {"no-unused-vars":1}
(function<T: A>(): T {}); import type A from "a"
// Additional rules: {"no-unused-vars":1}
import type {A} from "a"; (function<T: A>(): T {})
// Additional rules: {"no-unused-vars":1}
(function<T: A>(): T {}); import type {A} from "a"
// Additional rules: {"no-unused-vars":1}
(function<T: A>(): T {}); import type {a as A} from "a"
// Additional rules: {"no-unused-vars":1}
type A = {}; function x<Y: A>(i: Y) { i }; x()
// Additional rules: {"no-unused-vars":1}
function x<Y: A>(i: Y) { i }; type A = {}; x()
// Additional rules: {"no-unused-vars":1}
type A = {}; function x<Y: A.B.C>(i: Y) { i }; x()
// Additional rules: {"no-unused-vars":1}
function x<Y: A.B.C>(i: Y) { i }; type A = {}; x()
// Additional rules: {"no-unused-vars":1}
valid-syntax
Checks for simple Flow syntax errors.
The following patterns are considered problems:
function x(foo = "1": string) {}
// Message: "foo" parameter type annotation must be placed on left-hand side of assignment.
function x(foo = bar(): Type, baz = []: []) {}
// Message: "foo" parameter type annotation must be placed on left-hand side of assignment.
// Message: "baz" parameter type annotation must be placed on left-hand side of assignment.
The following patterns are not considered problems:
function x(foo: string = "1") {}
function x(foo: Type = bar()) {}
FAQs
Flowtype linting rules for ESLint.
The npm package eslint-plugin-flowtype receives a total of 3,559,665 weekly downloads. As such, eslint-plugin-flowtype popularity was classified as popular.
We found that eslint-plugin-flowtype demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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