$ npm install eslint-plugin-flowtype
Flow type linting rules for ESLint.
array-style-complex-type
array-style-simple-type
arrow-parens
boolean-style
define-flow-type
delimiter-dangle
enforce-line-break
generic-spacing
interface-id-match
newline-after-flow-annotation
no-dupe-keys
no-duplicate-type-union-intersection-members
no-existential-type
no-flow-fix-me-comments
no-internal-flow-type
no-mixed
no-mutable-array
no-primitive-constructor-types
no-types-missing-file-annotation
no-unused-expressions
no-weak-types
object-type-curly-spacing
object-type-delimiter
quotes
require-compound-type-alias
require-exact-type
require-indexer-name
require-inexact-type
require-parameter-type
require-readonly-react-props
require-return-type
require-types-at-top
require-valid-file-annotation
require-variable-type
semi
sort-keys
sort-type-union-intersection-members
space-after-type-colon
space-before-generic-bracket
space-before-type-colon
spread-exact-type
type-id-match
type-import-style
union-intersection-spacing
use-flow-type
use-read-only-spread
valid-syntax
npm install eslint --save-dev
npm install @babel/eslint-parser --save-dev
npm install eslint-plugin-flowtype --save-dev
parser
property to @babel/eslint-parser
.plugins
section and specify eslint-plugin-flowtype
as a plugin.{
"parser": "@babel/eslint-parser",
"plugins": [
"flowtype"
],
"rules": {
"flowtype/boolean-style": [
2,
"boolean"
],
"flowtype/define-flow-type": 1,
"flowtype/delimiter-dangle": [
2,
"never"
],
"flowtype/generic-spacing": [
2,
"never"
],
"flowtype/interface-id-match": [
2,
"^([A-Z][a-z0-9]+)+Type$"
],
"flowtype/no-mixed": 2,
"flowtype/no-primitive-constructor-types": 2,
"flowtype/no-types-missing-file-annotation": 2,
"flowtype/no-weak-types": 2,
"flowtype/object-type-delimiter": [
2,
"comma"
],
"flowtype/require-parameter-type": 2,
"flowtype/require-readonly-react-props": 0,
"flowtype/require-return-type": [
2,
"always",
{
"annotateUndefined": "never"
}
],
"flowtype/require-valid-file-annotation": 2,
"flowtype/semi": [
2,
"always"
],
"flowtype/space-after-type-colon": [
2,
"always"
],
"flowtype/space-before-generic-bracket": [
2,
"never"
],
"flowtype/space-before-type-colon": [
2,
"never"
],
"flowtype/type-id-match": [
2,
"^([A-Z][a-z0-9]+)+Type$"
],
"flowtype/union-intersection-spacing": [
2,
"always"
],
"flowtype/use-flow-type": 1,
"flowtype/valid-syntax": 1
},
"settings": {
"flowtype": {
"onlyFilesWithFlowAnnotation": false
}
}
}
This plugin exports a recommended configuration that enforces Flow type good practices.
To enable this configuration use the extends property in your .eslintrc
config file:
{
"extends": [
"plugin:flowtype/recommended"
],
"plugins": [
"flowtype"
]
}
See ESLint documentation for more information about extending configuration files.
The following are third-party submitted/ maintained configurations of eslint-plugin-flowtype
:
onlyFilesWithFlowAnnotation
When true
, only checks files with a @flow
annotation in the first comment.
{
"settings": {
"flowtype": {
"onlyFilesWithFlowAnnotation": true
}
}
}
array-style-complex-type
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces a particular annotation style of complex types.
Type is considered complex in these cases:
This rule takes one argument.
If it is 'verbose'
then a problem is raised when using Type[]
instead of Array<Type>
.
If it is 'shorthand'
then a problem is raised when using Array<Type>
instead of Type[]
.
The default value is 'verbose'
.
The following patterns are considered problems:
type X = (?string)[]
// Message: Use "Array<?string>", not "(?string)[]"
// Options: ["verbose"]
type X = (?string)[]
// Message: Use "Array<?string>", not "(?string)[]"
// Options: ["shorthand"]
type X = Array<?string>
// Message: Use "(?string)[]", not "Array<?string>"
// Options: ["shorthand"]
type X = Array<{foo: string}>
// Message: Use "{foo: string}[]", not "Array<{foo: string}>"
type X = (string | number)[]
// Message: Use "Array<string | number>", not "(string | number)[]"
type X = (string & number)[]
// Message: Use "Array<string & number>", not "(string & number)[]"
type X = [string, number][]
// Message: Use "Array<[string, number]>", not "[string, number][]"
type X = {foo: string}[]
// Message: Use "Array<{foo: string}>", not "{foo: string}[]"
type X = (string => number)[]
// Message: Use "Array<string => number>", not "(string => number)[]"
type X = {
foo: string,
bar: number
}[]
// Message: Use "Array<{ foo: string, bar: number }>", not "{ foo: string, bar: number }[]"
type X = {
foo: string,
bar: number,
quo: boolean,
hey: Date
}[]
// Message: Use "Array<Type>", not "Type[]"
The following patterns are not considered problems:
type X = Array<?string>
// Options: ["verbose"]
type X = Array<?string>
// Options: ["shorthand"]
type X = (?string)[]
// Options: ["shorthand"]
type X = Array<string>
// Options: ["shorthand"]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type X = Array<?string>
array-style-simple-type
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces a particular array type annotation style of simple types.
Type is considered simple in these cases:
This rule takes one argument.
If it is 'verbose'
then a problem is raised when using Type[]
instead of Array<Type>
.
If it is 'shorthand'
then a problem is raised when using Array<Type>
instead of Type[]
.
The default value is 'verbose'
.
The following patterns are considered problems:
type X = string[]
// Message: Use "Array<string>", not "string[]"
// Options: ["verbose"]
type X = string[]
// Message: Use "Array<string>", not "string[]"
// Options: ["shorthand"]
type X = Array<string>
// Message: Use "string[]", not "Array<string>"
type X = Date[]
// Message: Use "Array<Date>", not "Date[]"
type X = Promise<string>[]
// Message: Use "Array<Promise<string>>", not "Promise<string>[]"
type X = $Keys<{foo: string}>[]
// Message: Use "Array<$Keys<{foo: string}>>", not "$Keys<{foo: string}>[]"
type X = any[]
// Message: Use "Array<any>", not "any[]"
type X = mixed[]
// Message: Use "Array<mixed>", not "mixed[]"
type X = void[]
// Message: Use "Array<void>", not "void[]"
type X = null[]
// Message: Use "Array<null>", not "null[]"
type X = Promise<{
foo: string,
bar: number
}>[]
// Message: Use "Array<Promise<{ foo: string, bar: number }>>", not "Promise<{ foo: string, bar: number }>[]"
type X = Promise<{
foo: string,
bar: number,
quo: boolean
}>[]
// Message: Use "Array<Type>", not "Type[]"
The following patterns are not considered problems:
type X = Array<string>
// Options: ["verbose"]
type X = Array<string>
// Options: ["shorthand"]
type X = string[]
type X = Array<Array<string>>
// Options: ["verbose"]
type X = (?string)[]
// Options: ["verbose"]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type X = string[]
type X = Array
type X = typeof Array
arrow-parens
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces the consistent use of parentheses in arrow functions.
This rule has a string option and an object one.
String options are:
"always"
(default) requires parens around arguments in all cases."as-needed"
enforces no braces where they can be omitted.Object properties for variants of the "as-needed"
option:
"requireForBlockBody": true
modifies the as-needed rule in order to require parens if the function body is in an instructions block (surrounded by braces).The following patterns are considered problems:
a => {}
// Message: undefined
a => a
// Message: undefined
a => {
}
// Message: undefined
a.then(foo => {});
// Message: undefined
a.then(foo => a);
// Message: undefined
a(foo => { if (true) {}; });
// Message: undefined
a(async foo => { if (true) {}; });
// Message: undefined
// Options: ["as-needed"]
(a) => a
// Message: undefined
// Options: ["as-needed"]
(a,) => a
// Message: undefined
// Options: ["as-needed"]
async (a) => a
// Message: undefined
// Options: ["as-needed"]
async(a) => a
// Message: undefined
// Options: ["as-needed",{"requireForBlockBody":true}]
a => {}
// Message: undefined
// Options: ["as-needed",{"requireForBlockBody":true}]
(a) => a
// Message: undefined
// Options: ["as-needed",{"requireForBlockBody":true}]
async a => {}
// Message: undefined
// Options: ["as-needed",{"requireForBlockBody":true}]
async (a) => a
// Message: undefined
// Options: ["as-needed",{"requireForBlockBody":true}]
async(a) => a
// Message: undefined
The following patterns are not considered problems:
() => {}
(a) => {}
(a) => a
(a) => {
}
a.then((foo) => {});
a.then((foo) => { if (true) {}; });
a.then(async (foo) => { if (true) {}; });
// Options: ["always"]
() => {}
// Options: ["always"]
(a) => {}
// Options: ["always"]
(a) => a
// Options: ["always"]
(a) => {
}
// Options: ["always"]
a.then((foo) => {});
// Options: ["always"]
a.then((foo) => { if (true) {}; });
// Options: ["always"]
a.then(async (foo) => { if (true) {}; });
// Options: ["as-needed"]
() => {}
// Options: ["as-needed"]
a => {}
// Options: ["as-needed"]
a => a
// Options: ["as-needed"]
([a, b]) => {}
// Options: ["as-needed"]
({ a, b }) => {}
// Options: ["as-needed"]
(a = 10) => {}
// Options: ["as-needed"]
(...a) => a[0]
// Options: ["as-needed"]
(a, b) => {}
// Options: ["as-needed"]
async ([a, b]) => {}
// Options: ["as-needed"]
async (a, b) => {}
// Options: ["as-needed"]
(a: T) => a
// Options: ["as-needed"]
(a): T => a
// Options: ["as-needed",{"requireForBlockBody":true}]
() => {}
// Options: ["as-needed",{"requireForBlockBody":true}]
a => a
// Options: ["as-needed",{"requireForBlockBody":true}]
([a, b]) => {}
// Options: ["as-needed",{"requireForBlockBody":true}]
([a, b]) => a
// Options: ["as-needed",{"requireForBlockBody":true}]
({ a, b }) => {}
// Options: ["as-needed",{"requireForBlockBody":true}]
({ a, b }) => a + b
// Options: ["as-needed",{"requireForBlockBody":true}]
(a = 10) => {}
// Options: ["as-needed",{"requireForBlockBody":true}]
(...a) => a[0]
// Options: ["as-needed",{"requireForBlockBody":true}]
(a, b) => {}
// Options: ["as-needed",{"requireForBlockBody":true}]
a => ({})
// Options: ["as-needed",{"requireForBlockBody":true}]
async a => ({})
// Options: ["as-needed",{"requireForBlockBody":true}]
async a => a
// Options: ["as-needed",{"requireForBlockBody":true}]
(a: T) => a
// Options: ["as-needed",{"requireForBlockBody":true}]
(a): T => a
// Options: ["always",{"requireForBlockBody":true}]
<T>(a: T) => a
// Options: ["as-needed",{"requireForBlockBody":false}]
<T>(a: T) => { return a; }
// Options: ["always",{"requireForBlockBody":true}]
<T>(a: T) => { return a; }
// Options: ["as-needed",{"requireForBlockBody":true}]
<T>(a: T) => { return a; }
// Options: ["as-needed",{"requireForBlockBody":true}]
(a): %checks => typeof a === "number"
boolean-style
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces a particular style for boolean type annotations. This rule takes one argument.
If it is 'boolean'
then a problem is raised when using bool
instead of boolean
.
If it is 'bool'
then a problem is raised when using boolean
instead of bool
.
The default value is 'boolean'
.
The following patterns are considered problems:
type X = bool
// Message: Use "boolean", not "bool"
// Options: ["boolean"]
type X = bool
// Message: Use "boolean", not "bool"
// Options: ["bool"]
type X = boolean
// Message: Use "bool", not "boolean"
The following patterns are not considered problems:
type X = boolean
// Options: ["boolean"]
type X = boolean
// Options: ["bool"]
type X = bool
// Options: ["boolean"]
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type X = bool
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}
declare type A = number
// Additional rules: {"no-undef":2}
opaque 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}
declare interface A {}
// Additional rules: {"no-undef":2}
({ a: ({b() {}}: AType) })
// Additional rules: {"no-undef":2}
type X = {Y<AType>(): BType}
// Additional rules: {"no-undef":2}
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
/**
* Copyright 2019 no corp
* @flow
*/
type Foo = $ReadOnly<{}>
// 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"]}
declare type A = number
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
opaque 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"]}
declare interface A {}
// 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"]}
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
/**
* Copyright 2019 no corp
* @flow
*/
type Foo = $ReadOnly<{}>
// Additional rules: {"no-undef":2,"no-use-before-define":[2,"nofunc"]}
delimiter-dangle
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces consistent use of trailing commas in Object and Tuple annotations.
This rule takes three arguments where the possible values are the same as ESLint's default comma-dangle
rule:
'never'
....
). The default value is 'never'
.If it is 'never'
then a problem is raised when there is a trailing comma.
If it is 'always'
then a problem is raised when there is no trailing comma.
If it is 'always-multiline'
then a problem is raised when there is no trailing comma on a multi-line definition, or there is a trailing comma on a single-line definition.
If it is 'only-multiline'
then a problem is raised when there is a trailing comma on a single-line definition. It allows, but does not enforce, trailing commas on multi-line definitions.
The following patterns are considered problems:
type X = { foo: string, }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = { foo: string, }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = { foo: string; }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = {
foo: string,
}
// Message: Unexpected trailing delimiter
// Options: ["always"]
type X = { foo: string }
// Message: Missing trailing delimiter
// Options: ["always"]
type X = {
foo: string
}
// Message: Missing trailing delimiter
// Options: ["always-multiline"]
type X = { foo: string, }
// Message: Unexpected trailing delimiter
// Options: ["always-multiline"]
type X = {
foo: string
}
// Message: Missing trailing delimiter
// Options: ["only-multiline"]
type X = { foo: string; }
// Message: Unexpected trailing delimiter
// Options: ["always","never"]
interface X { foo: string; }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = { [key: string]: number, }
// Message: Unexpected trailing delimiter
// Options: ["always"]
type X = { [key: string]: number }
// Message: Missing trailing delimiter
// Options: ["always-multiline"]
type X = { [key: string]: number, }
// Message: Unexpected trailing delimiter
// Options: ["always-multiline"]
type X = {
[key: string]: number
}
// Message: Missing trailing delimiter
// Options: ["only-multiline"]
type X = { [key: string]: number; }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = { [key: string]: number, foo: string, }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = {
[key: string]: number,
foo: string,
}
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = {
[key: string]: number,
aReallyLongPropertyNameHere: string,
}
// Message: Unexpected trailing delimiter
// Options: ["always"]
type X = { [key: string]: number, foo: string }
// Message: Missing trailing delimiter
// Options: ["always"]
type X = {
[key: string]: number;
foo: string
}
// Message: Missing trailing delimiter
// Options: ["always-multiline"]
type X = { [key: string]: number, foo: string, }
// Message: Unexpected trailing delimiter
// Options: ["always-multiline"]
type X = {
[key: string]: number,
foo: string
}
// Message: Missing trailing delimiter
// Options: ["only-multiline"]
type X = { [key: string]: number, foo: string, }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = { foo: string, [key: string]: number, }
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = {
foo: string,
[key: string]: number,
}
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = {
aReallyLongPropertyNameHere: string,
[key: string]: number,
}
// Message: Unexpected trailing delimiter
// Options: ["always"]
type X = { foo: string, [key: string]: number }
// Message: Missing trailing delimiter
// Options: ["always"]
type X = { foo: string; [key: string]: number }
// Message: Missing trailing delimiter
// Options: ["always-multiline"]
type X = { foo: string, [key: string]: number; }
// Message: Unexpected trailing delimiter
// Options: ["always-multiline"]
type X = {
foo: string,
[key: string]: number
}
// Message: Missing trailing delimiter
// Options: ["only-multiline"]
type X = { foo: string, [key: string]: number; }
// Message: Unexpected trailing delimiter
type X = { ..., }
// Message: Unexpected trailing delimiter
type X = { ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = { ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = { ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","always"]
type X = { ... }
// Message: Missing trailing delimiter
// Options: ["never","never","always-multiline"]
type X = { ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","always-multiline"]
type X = { ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","only-multiline"]
type X = { ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","only-multiline"]
type X = { ...; }
// Message: Unexpected trailing delimiter
type X = {
...,
}
// Message: Unexpected trailing delimiter
type X = {
...;
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = {
...,
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = {
...;
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","always"]
type X = {
...
}
// Message: Missing trailing delimiter
// Options: ["never","never","always-multiline"]
type X = {
...
}
// Message: Missing trailing delimiter
type X = { foo: string, ..., }
// Message: Unexpected trailing delimiter
type X = { foo: string; ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = { foo: string, ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = { foo: string; ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","always"]
type X = { foo: string, ... }
// Message: Missing trailing delimiter
// Options: ["never","never","always-multiline"]
type X = { foo: string, ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","always-multiline"]
type X = { foo: string; ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","only-multiline"]
type X = { foo: string, ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","only-multiline"]
type X = { foo: string; ...; }
// Message: Unexpected trailing delimiter
type X = {
foo: string,
...,
}
// Message: Unexpected trailing delimiter
type X = {
foo: string;
...;
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = {
foo: string,
...,
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = {
foo: string;
...;
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","always"]
type X = {
foo: string,
...
}
// Message: Missing trailing delimiter
// Options: ["never","never","always-multiline"]
type X = {
foo: string,
...
}
// Message: Missing trailing delimiter
type X = { [key: string]: number, ..., }
// Message: Unexpected trailing delimiter
type X = { [key: string]: number; ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = { [key: string]: number, ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = { [key: string]: number; ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","always"]
type X = { [key: string]: number, ... }
// Message: Missing trailing delimiter
// Options: ["never","never","always-multiline"]
type X = { [key: string]: number, ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","always-multiline"]
type X = { [key: string]: number; ...; }
// Message: Unexpected trailing delimiter
// Options: ["never","never","only-multiline"]
type X = { [key: string]: number, ..., }
// Message: Unexpected trailing delimiter
// Options: ["never","never","only-multiline"]
type X = { [key: string]: number; ...; }
// Message: Unexpected trailing delimiter
type X = {
[key: string]: number,
...,
}
// Message: Unexpected trailing delimiter
type X = {
[key: string]: number;
...;
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = {
[key: string]: number,
...,
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","never"]
type X = {
[key: string]: number;
...;
}
// Message: Unexpected trailing delimiter
// Options: ["never","never","always"]
type X = {
[key: string]: number,
...
}
// Message: Missing trailing delimiter
// Options: ["never","never","always-multiline"]
type X = {
[key: string]: number,
...
}
// Message: Missing trailing delimiter
type X = [string, number,]
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = [string, number,]
// Message: Unexpected trailing delimiter
// Options: ["never"]
type X = [
string,
number,
]
// Message: Unexpected trailing delimiter
// Options: ["always"]
type X = [string, number]
// Message: Missing trailing delimiter
// Options: ["always"]
type X = [
string,
number
]
// Message: Missing trailing delimiter
// Options: ["always-multiline"]
type X = [string, number,]
// Message: Unexpected trailing delimiter
// Options: ["always-multiline"]
type X = [
foo, string
]
// Message: Missing trailing delimiter
// Options: ["only-multiline"]
type X = [ number, string, ]
// Message: Unexpected trailing delimiter
The following patterns are not considered problems:
type X = { foo: string }
// Options: ["never"]
type X = { foo: string }
// Options: ["always"]
type X = { foo: string, }
// Options: ["always"]
type X = { foo: string; }
// Options: ["never"]
type X = {
foo: string
}
// Options: ["always"]
type X = {
foo: string,
}
// Options: ["always-multiline"]
type X = { foo: string }
// Options: ["always-multiline"]
type X = {
foo: string,
}
// Options: ["always-multiline"]
type X = {
foo: string;
}
// Options: ["only-multiline"]
type X = { foo: string }
// Options: ["only-multiline"]
type X = {
foo: string
}
// Options: ["only-multiline"]
type X = {
foo: string,
}
// Options: ["only-multiline"]
type X = {
foo: string;
}
// Options: ["never","always"]
interface X { foo: string; }
// Options: ["never"]
type X = {}
// Options: ["always"]
type X = {}
// Options: ["always-multiline"]
type X = {}
// Options: ["only-multiline"]
type X = {}
// Options: ["never"]
type X = { [key: string]: number }
// Options: ["always"]
type X = { [key: string]: number, }
// Options: ["always"]
type X = { [key: string]: number; }
// Options: ["always-multiline"]
type X = { [key: string]: number }
// Options: ["always-multiline"]
type X = {
[key: string]: number,
}
// Options: ["only-multiline"]
type X = {
[key: string]: number,
}
// Options: ["only-multiline"]
type X = {
[key: string]: number
}
// Options: ["only-multiline"]
type X = { [key: string]: number }
// Options: ["never"]
type X = { [key: string]: number, foo: string }
// Options: ["always"]
type X = { [key: string]: number, foo: string, }
// Options: ["always"]
type X = { [key: string]: number; foo: string; }
// Options: ["always-multiline"]
type X = { [key: string]: number, foo: string }
// Options: ["always-multiline"]
type X = {
[key: string]: number,
foo: string,
}
// Options: ["only-multiline"]
type X = {
[key: string]: number,
foo: string,
}
// Options: ["only-multiline"]
type X = {
[key: string]: number;
foo: string
}
// Options: ["only-multiline"]
type X = { [key: string]: number, foo: string }
// Options: ["never"]
type X = { foo: string, [key: string]: number }
// Options: ["always"]
type X = { foo: string, [key: string]: number, }
// Options: ["always"]
type X = { foo: string; [key: string]: number; }
// Options: ["always-multiline"]
type X = { foo: string, [key: string]: number }
// Options: ["always-multiline"]
type X = {
foo: string,
[key: string]: number,
}
// Options: ["only-multiline"]
type X = {
foo: string,
[key: string]: number,
}
// Options: ["only-multiline"]
type X = {
foo: string;
[key: string]: number
}
// Options: ["only-multiline"]
type X = { foo: string, [key: string]: number }
type X = { ... }
// Options: ["never","never","never"]
type X = { ... }
// Options: ["never","never","always"]
type X = { ..., }
// Options: ["never","never","always-multiline"]
type X = { ... }
// Options: ["never","never","only-multiline"]
type X = { ... }
type X = {
...
}
// Options: ["never","never","never"]
type X = {
...
}
// Options: ["never","never","always"]
type X = {
...,
}
// Options: ["never","never","always"]
type X = {
...;
}
// Options: ["never","never","always-multiline"]
type X = {
...,
}
// Options: ["never","never","always-multiline"]
type X = {
...;
}
// Options: ["never","never","only-multiline"]
type X = {
...
}
// Options: ["never","never","only-multiline"]
type X = {
...,
}
// Options: ["never","never","only-multiline"]
type X = {
...;
}
type X = { foo: string, ... }
// Options: ["never","never","never"]
type X = { foo: string, ... }
// Options: ["never","never","always"]
type X = { foo: string, ..., }
// Options: ["never","never","always"]
type X = { foo: string; ...; }
// Options: ["never","never","always-multiline"]
type X = { foo: string, ... }
// Options: ["never","never","only-multiline"]
type X = { foo: string, ... }
type X = {
foo: string,
...
}
// Options: ["never","never","never"]
type X = {
foo: string,
...
}
// Options: ["never","never","always"]
type X = {
foo: string,
...,
}
// Options: ["never","never","always"]
type X = {
foo: string;
...;
}
// Options: ["never","never","always-multiline"]
type X = {
foo: string,
...,
}
// Options: ["never","never","always-multiline"]
type X = {
foo: string;
...;
}
// Options: ["never","never","only-multiline"]
type X = {
foo: string,
...
}
// Options: ["never","never","only-multiline"]
type X = {
foo: string,
...,
}
// Options: ["never","never","only-multiline"]
type X = {
foo: string,
...;
}
// Options: ["never","never","never"]
type X = { [key: string]: number, ... }
// Options: ["never","never","always"]
type X = { [key: string]: number, ..., }
// Options: ["never","never","always"]
type X = { [key: string]: number; ...; }
// Options: ["never","never","always-multiline"]
type X = { [key: string]: number, ... }
// Options: ["never","never","only-multiline"]
type X = { [key: string]: number, ... }
// Options: ["never","never","never"]
type X = {
[key: string]: number,
...
}
// Options: ["never","never","always"]
type X = {
[key: string]: number,
...,
}
// Options: ["never","never","always"]
type X = {
[key: string]: number;
...;
}
// Options: ["never","never","always-multiline"]
type X = {
[key: string]: number,
...,
}
// Options: ["never","never","always-multiline"]
type X = {
[key: string]: number;
...;
}
// Options: ["never","never","only-multiline"]
type X = {
[key: string]: number,
...
}
// Options: ["never","never","only-multiline"]
type X = {
[key: string]: number,
...,
}
// Options: ["never","never","only-multiline"]
type X = {
[key: string]: number;
...;
}
type X = [string, number]
// Options: ["never"]
type X = [string, number]
// Options: ["never"]
type X = [
string,
number
]
// Options: ["always"]
type X = [string, number,]
// Options: ["always"]
type X = [
string,
number,
]
// Options: ["always-multiline"]
type X = [ foo, string ]
// Options: ["always-multiline"]
type X = [
foo, string,
]
// Options: ["only-multiline"]
type X = [ number, string ]
// Options: ["only-multiline"]
type X = [
number,
string
]
// Options: ["only-multiline"]
type X = [
number,
string,
]
// Options: ["never"]
type X = []
// Options: ["always"]
type X = []
// Options: ["always-multiline"]
type X = []
// Options: ["only-multiline"]
type X = []
enforce-line-break
This rule enforces line breaks between type definitions.
The following patterns are considered problems:
type baz = 6;
const hi = 2;
// Message: New line required below type declaration
const foo = 6;
type hi = 2;
// Message: New line required above type declaration
const som = "jes";
// a comment
type fed = "hed";
// Message: New line required above type declaration
type som = "jes";
// a comment
const fed = "hed";
// Message: New line required below type declaration
type hello = 34;
const som = "jes";
type fed = "hed";
// Message: New line required below type declaration
// Message: New line required above type declaration
const a = 5;
export type hello = 34;
// Message: New line required above type declaration
const a = 5;
// a comment
export type hello = 34;
// Message: New line required above type declaration
const a = 5;
/**
* a jsdoc block
*/
type hello = 34;
// Message: New line required above type declaration
The following patterns are not considered problems:
type gjs = 6;
type gjs = 6;
type hi = 2;
type X = 4;
const red = "serpent";
console.log("hello");
// number or string
type Y = string | number;
// resting + sleep
type snooze = "dreaming" | "";
type Props = {
accountBalance: string | number,
accountNumber: string | number,
};
const x = 4;
const y = 489;
// Some Comment
type Props = {
accountBalance: string | number,
accountNumber: string | number,
};
type RoadT = "grass" | "gravel" | "cement";
// @flow
type A = string
generic-spacing
The --fix
option on the command line automatically fixes problems reported by this rule.
Enforces consistent spacing within generic type annotation parameters.
This rule takes one argument. If it is 'never'
then a problem is raised when there is a space surrounding the generic type parameters. If it is 'always'
then a problem is raised when there is no space surrounding the generic type parameters.
The default value is 'never'
.
The following patterns are considered problems:
type X = Promise< string>
// Message: There must be no space at start of "Promise" generic type annotation
// Options: ["never"]
type X = Promise< string>
// Message: There must be no space at start of "Promise" generic type annotation
type X = FooBar<string >
// Message: There must be no space at end of "FooBar" generic type annotation
type X = Promise< string >
// Message: There must be no space at start of "Promise" generic type annotation
// Message: There must be no space at end of "Promise" generic type annotation
type X = Promise< (foo), bar, (((baz))) >
// Message: There must be no space at start of "Promise" generic type annotation
// Message: There must be no space at end of "Promise" generic type annotation
// Options: ["always"]
type X = Promise<string >
// Message: There must be a space at start of "Promise" generic type annotation
// Options: ["always"]
type X = FooBar< string>
// Message: There must be a space at end of "FooBar" generic type annotation
// Options: ["always"]
type X = Promise<string>
// Message: There must be a space at start of "Promise" generic type annotation
// Message: There must be a space at end of "Promise" generic type annotation
// Options: ["always"]
type X = Promise<(foo), bar, (((baz)))>
// Message: There must be a space at start of "Promise" generic type annotation
// Message: There must be a space at end of "Promise" generic type annotation
// Options: ["always"]
type X = FooBar< string >
// Message: There must be one space at start of "FooBar" generic type annotation
// Options: ["always"]
type X = FooBar< string >
// Message: There must be one space at end of "FooBar" generic type annotation
// Options: ["always"]
type X = Promise< (foo), bar, (((baz))) >
// Message: There must be one space at start of "Promise" generic type annotation
// Message: There must be one space at end of "Promise" generic type annotation
The following patterns are not considered problems:
type X = Promise<string>
type X = Promise<(string)>
type X = Promise<(foo), bar, (((baz)))>
type X = Promise<
(foo),
bar,
(((baz)))
>
type X = Promise<
(foo),
bar,
(((baz)))
>
// Options: ["always"]
type X = Promise< string >
// Options: ["always"]
type X = Promise< (string) >
// Options: ["always"]
type X = Promise< (foo), bar, (((baz))) >
interface-id-match
Enforces a consistent naming pattern for interfaces.
This rule requires a text RegExp:
{
"rules": {
"flowtype/interface-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:
interface foo{};
// Message: Interface identifier 'foo' does not match pattern '/^([A-Z][a-z0-9]*)+Type$/u'.
// Options: ["^foo$"]
interface FooType{};
// Message: Interface identifier 'FooType' does not match pattern '/^foo$/u'.
The following patterns are not considered problems:
interface FooType {};
// Options: ["^foo$"]
interface foo {};
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
interface foo {};
newline-after-flow-annotation
This rule requires an empty line after the Flow annotation.
The rule has a string option:
"always"
(default): Enforces that @flow
annotations be followed by an empty line, separated by newline (LF)"always-windows"
: Identical to "always", but will use a CRLF when autofixing"never"
: Enforces that @flow
annotations are not followed by empty lines{
"rules": {
"flowtype/newline-after-flow-annotation": [
2,
"always"
]
}
}
The following patterns are considered problems:
// @flow
import Foo from './foo';
// Message: Expected newline after flow annotation
// Options: ["always"]
// @flow
import Foo from './foo';
// Message: Expected newline after flow annotation
// Options: ["always-windows"]
// @flow
import Foo from './foo';
// Message: Expected newline after flow annotation
// Options: ["never"]
// @flow
// Message: Expected no newline after flow annotation
The following patterns are not considered problems:
// Options: ["always"]
// @flow
import Foo from './foo';
// Options: ["always-windows"]
// @flow
import Foo from './foo';
// Options: ["never"]
// @flow
import Foo from './foo';
no-dupe-keys
Checks for duplicate properties in Object annotations.
This rule mirrors ESLint's no-dupe-keys rule.
{
"rules": {
"flowtype/no-dupe-keys": 2
}
}
The following patterns are considered problems:
type f = { a: number, b: string, a: number }
// Message: Duplicate property.
type f = { a: number, b: string, a: string }
// Message: Duplicate property.
type f = { get(key: "a"): string, get(key: "a"): string }
// Message: Duplicate property.
type f = { get(key: 1): string, get(key: 1): string }
// Message: Duplicate property.
type f = { get(key: 1.1): string, get(key: 1.1): string }
// Message: Duplicate property.
type f = { get(key: true): string, get(key: true): string }
// Message: Duplicate property.
type f = { get(key: {a: 1}): string, get(key: {a: 1}):string }
// Message: Duplicate property.
var a = "a"; type f = { get(key: a): string, get(key: a): string }
// Message: Duplicate property.
var b = 1; type f = { get(key: b): string, get(key: b): string }
// Message: Duplicate property.
var c = true; type f = { get(key: c): string, get(key: c): string }
// Message: Duplicate property.
var d = {}; type f = { get(key: d): string, get(key: d): string }
// Message: Duplicate property.
var e = []; type f = { get(key: e): string, get(key: e): string }
// Message: Duplicate property.
var e = [1, "a"]; type f = { get(key: e): string, get(key: e): string }
// Message: Duplicate property.
function fn() {}; type f = { get(key: fn): string, get(key: fn): string }
// Message: Duplicate property.
The following patterns are not considered problems:
type FooType = { a: number, b: string, c: number }
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
type FooType = { a: number, b: string, a: number }
type f = { get(key: "a"): string, get(key: "b"): string }
type f = { get(key: 1): string, get(key: 2): string }
type f = { get(key: 1.1): string, get(key: 1.2): string }
type f = { get(key: true): string, get(key: false): string }
type f = { get(key: ["a", 1]): string, get(key: ["a", 2]): string }
type f = { get(key: ["a", ["b", 1]]): string, get(key: ["a", ["b", 2]]): string }
type f = { a: number, b: string, c: number }
type f = { get(key: "a"): string, get(key: "b"): string }
type f = { get(key: "a"): string, get(key: "a", key2: "b"): string }
type f = { get(key: "a"): string, get(key: 1): string }
type f = { get(key: { a: 1 }): string, get(key: { a: 2 }): string}
var a = {}; var b = {}; type f = { get(key: a): string, get(key: b): string }
var a = 1; var b = 1; type f = { get(key: a): string, get(key: b): string }
type a = { b: <C>(config: { ...C, key: string}) => C }
export interface Foo { get foo(): boolean; get bar(): string; }
no-duplicate-type-union-intersection-members
The --fix
option on the command line automatically fixes problems reported by this rule.
Checks for duplicate members of a type union/intersection.
You can disable checking intersection types using checkIntersections
.
true
(default) - check for duplicate members of intersection members.false
- do not check for duplicate members of intersection members.{
"rules": {
"flowtype/no-duplicate-type-union-intersection-members": [
2,
{
"checkIntersections": true
}
]
}
}
You can disable checking union types using checkUnions
.
true
(default) - check for duplicate members of union members.false
- do not check for duplicate members of union members.{
"rules": {
"flowtype/no-duplicate-type-union-intersection-members": [
2,
{
"checkUnions": true
}
]
}
}
The following patterns are considered problems:
type A = 1 | 2 | 3 | 1;
// Message: Duplicate union member found "1".
type B = 'foo' | 'bar' | 'foo';
// Message: Duplicate union member found "'foo'".
type C = A | B | A | B;
// Message: Duplicate union member found "A".
// Message: Duplicate union member found "B".
type C = A & B & A & B;
// Message: Duplicate intersection member found "A".
// Message: Duplicate intersection member found "B".
The following patterns are not considered problems:
type A = 1 | 2 | 3;
type B = 'foo' | 'bar';
type C = A | B;
type C = A & B;
no-existential-type
Disallows use of the existential type (*). See more
{
"rules": {
"flowtype/no-existential-type": 2
}
}
The following patterns are considered problems:
type T = *;
// Message: Unexpected use of existential type (*).
type T = U<*, *>;
// Message: Unexpected use of existential type (*).
// Message: Unexpected use of existential type (*).
const f: (*) => null = () => null;
// Message: Unexpected use of existential type (*).
The following patterns are not considered problems:
type T = string | null
no-flow-fix-me-comments
Disallows $FlowFixMe
comment suppressions.
This is especially useful as a warning to ensure instances of $FlowFixMe
in your codebase get fixed over time.
This rule takes an optional RegExp that comments a text RegExp that makes the supression valid.
{
"rules": {
"flowtype/no-flow-fix-me-comments": [
1,
"TODO\s+[0-9]+"
]
}
}
The following patterns are considered problems:
// $FlowFixMe I am doing something evil here
const text = 'HELLO';
// Message: $FlowFixMe is treated as `any` and must be fixed.
// Options: ["TODO [0-9]+"]
// $FlowFixMe I am doing something evil here
const text = 'HELLO';
// Message: $FlowFixMe is treated as `any` and must be fixed. Fix it or match `/TODO [0-9]+/u`.
// Options: ["TODO [0-9]+"]
// $FlowFixMe TODO abc 47 I am doing something evil here
const text = 'HELLO';
// Message: $FlowFixMe is treated as `any` and must be fixed. Fix it or match `/TODO [0-9]+/u`.
// $$FlowFixMeProps I am doing something evil here
const text = 'HELLO';
// Message: $FlowFixMe is treated as `any` and must be fixed.
// Options: ["TODO [0-9]+"]
// $FlowFixMeProps I am doing something evil here
const text = 'HELLO';
// Message: $FlowFixMe is treated as `any` and must be fixed. Fix it or match `/TODO [0-9]+/u`.
The following patterns are not considered problems:
const text = 'HELLO';
// Options: ["TODO [0-9]+"]
// $FlowFixMe TODO 48
const text = 'HELLO';
no-internal-flow-type
Warns against using internal Flow types such as React$Node
, React$Ref
and others and suggests using public alternatives instead (React.Node
, React.Ref
, …).
The following patterns are considered problems:
type X = React$AbstractComponent<Config, Instance>
// Message: Type identifier 'React$AbstractComponent' is not allowed. Use 'React.AbstractComponent' instead.
type X = React$ChildrenArray<string>
// Message: Type identifier 'React$ChildrenArray' is not allowed. Use 'React.ChildrenArray' instead.
type X = React$ComponentType<Props>
// Message: Type identifier 'React$ComponentType' is not allowed. Use 'React.ComponentType' instead.
type X = React$Config<Prosp, DefaultProps>
// Message: Type identifier 'React$Config' is not allowed. Use 'React.Config' instead.
type X = React$Element<typeof Component>
// Message: Type identifier 'React$Element' is not allowed. Use 'React.Element' instead.
type X = React$ElementConfig<typeof Component>
// Message: Type identifier 'React$ElementConfig' is not allowed. Use 'React.ElementConfig' instead.
type X = React$ElementProps<typeof Component>
// Message: Type identifier 'React$ElementProps' is not allowed. Use 'React.ElementProps' instead.
type X = React$ElementRef<typeof Component>
// Message: Type identifier 'React$ElementRef' is not allowed. Use 'React.ElementRef' instead.
type X = React$ElementType
// Message: Type identifier 'React$ElementType' is not allowed. Use 'React.ElementType' instead.
type X = React$Key
// Message: Type identifier 'React$Key' is not allowed. Use 'React.Key' instead.
type X = React$Node
// Message: Type identifier 'React$Node' is not allowed. Use 'React.Node' instead.
type X = React$Ref<typeof Component>
// Message: Type identifier 'React$Ref' is not allowed. Use 'React.Ref' instead.
type X = React$StatelessFunctionalComponent<Props>
// Message: Type identifier 'React$StatelessFunctionalComponent' is not allowed. Use 'React.StatelessFunctionalComponent' instead.
The following patterns are not considered problems:
type X = React.AbstractComponent<Config, Instance>
type X = React.ChildrenArray<string>
type X = React.ComponentType<Props>
type X = React.Config<Props, DefaultProps>
type X = React.Element<typeof Component>
type X = React.ElementConfig<typeof Component>
type X = React.ElementProps<typeof Component>
type X = React.ElementRef<typeof Component>
type X = React.ElementType
type X = React.Key
type X = React.Node
type X = React.Ref<typeof Component>
type X = React.StatelessFunctionalComponent<Props>
type X = React$Rocks
no-mixed
Warns against "mixed" type annotations. These types are not strict enough and could often be made more specific.
The following patterns are considered problems:
The following patterns are considered problems:
function foo(thing): mixed {}
// Message: Unexpected use of mixed type
function foo(thing): Promise<mixed> {}
// Message: Unexpected use of mixed type
function foo(thing): Promise<Promise<mixed>> {}
// Message: Unexpected use of mixed type
The following patterns are not considered problems:
function foo(thing): string {}
function foo(thing): Promise<string> {}
function foo(thing): Promise<Promise<string>> {}
(foo?: string) => {}
(foo: ?string) => {}
(foo: { a: string }) => {}
(foo: { a: ?string }) => {}
(foo: string[]) => {}
type Foo = string
type Foo = { a: string }
type Foo = { (a: string): string }
function foo(thing: string) {}
var foo: string
class Foo { props: string }
no-mutable-array
The --fix
option on the command line automatically fixes problems reported by this rule.
Requires use of $ReadOnlyArray
instead of just Array
or array shorthand notation. $ReadOnlyArray
is immutable array collection type and the superclass of Array and tuple types in Flow. Use of $ReadOnlyArray
instead of Array
can solve some "problems" in typing with Flow (e.g., 1, 2).
General reasons for using immutable data structures:
Note that initialization of a variable with an empty array is considered valid (e.g., const values: Array<string> = [];
). This behavior resembles the behavior of Flow's unsealed objects, as it is assumed that empty array is intended to be mutated.
The following patterns are considered problems:
type X = Array<string>
// Message: Use "$ReadOnlyArray" instead of "Array"
type X = string[]
// Message: Use "$ReadOnlyArray" instead of array shorthand notation
const values: Array<Array<string>> = [];
// Message: Use "$ReadOnlyArray" instead of "Array"
let values: Array<Array<string>>;
// Message: Use "$ReadOnlyArray" instead of "Array"
// Message: Use "$ReadOnlyArray" instead of "Array"
The following patterns are not considered problems:
type X = $ReadOnlyArray<string>
const values: Array<$ReadOnlyArray<string>> = [];
const values: $ReadOnlyArray<string>[] = [];
const values: Array<$ReadOnlyArray<string>> = new Array();
const values: Array<$ReadOnlyArray<string>> = Array();
no-primitive-constructor-types
Disallows use of primitive constructors as types, such as Boolean
, Number
and String
. See more.
{
"rules": {
"flowtype/no-primitive-constructor-types": 2
}
}
The following patterns are considered problems:
type x = Number
// Message: Unexpected use of Number constructor type.
type x = String
// Message: Unexpected use of String constructor type.
type x = Boolean
// Message: Unexpected use of Boolean constructor type.
type x = { a: Number }
// Message: Unexpected use of Number constructor type.
type x = { a: String }
// Message: Unexpected use of String constructor type.
type x = { a: Boolean }
// Message: Unexpected use of Boolean constructor type.
(x: Number) => {}
// Message: Unexpected use of Number constructor type.
(x: String) => {}
// Message: Unexpected use of String constructor type.
(x: Boolean) => {}
// Message: Unexpected use of Boolean constructor type.
The following patterns are not considered problems:
type x = number
type x = string
type x = boolean
type x = { a: number }
type x = { a: string }
type x = { a: boolean }
(x: number) => {}
(x: string) => {}
(x: boolean) => {}
type x = MyNumber
type x = MyString
type x = MyBoolean
no-types-missing-file-annotation
Disallows Flow type imports, aliases, and annotations in files missing a valid Flow file declaration (or a @noflow annotation).
{
"rules": {
"flowtype/no-types-missing-file-annotation": 2
}
}
The following patterns are considered problems:
const x: number = 42;
// Message: Type annotations require valid Flow declaration.
type FooType = number;
// Message: Type aliases require valid Flow declaration.
import type A from "a"
// Message: Type imports require valid Flow declaration.
import type {A} from "a"
// Message: Type imports require valid Flow declaration.
import {type A} from "a"
// Message: Type imports require valid Flow declaration.
export type {A} from "a"
// Message: Type exports require valid Flow declaration.
function t<T>(): T{}
// Message: Type annotations require valid Flow declaration.
// Settings: {"flowtype":{"onlyFilesWithFlowAnnotation":true}}
const x: number = 42;
// Message: Type annotations require valid Flow declaration.
The following patterns are not considered problems:
// @flow
const x: number = 42;
/* @flow weak */
type FooType = number;
/* @noflow */
type FooType = number;
/* @noflow */
import type A from "a"
/* @noflow */
import {type A} from "a"
/* @noflow */
export type {A} from "a"
// an unrelated comment
// @flow
export type {A} from "a"
no-unused-expressions
An extension of ESLint's no-unused-expressions
.
This rule ignores type cast expressions and optional call expressions, but otherwise behaves the same as ESLint's
no-unused-expressions
.
Bare type casts are useful, for example to assert the exhaustiveness of a switch
:
type Action
= { type: 'FOO', doFoo: (_: number) => void }
| { type: 'BAR', doBar: (_: string) => void };
type State = { foo: number, bar: string };
function runFooBar(action: Action, state: State): void {
switch (action.type) {
case 'FOO':
doFoo(state.foo);
break;
case 'BAR':
doBar(state.bar);
break;
default:
(action: empty); // type error when `Action` is extended with new types
console.error(`Impossible action: ${action.toString()}`);
}
}
This rule takes the same arguments as ESLint's no-unused-expressions
. See
that rule's documentation for details.
The following patterns are considered problems:
foo + 1
// Message: Expected an assignment or function call and instead saw an expression.
x?.y
// Message: Expected an assignment or function call and instead saw an expression.
The following patterns are not considered problems:
(foo: number)
x?.y()
no-weak-types
Warns against weak type annotations any, Object and Function. These types can cause flow to silently skip over portions of your code, which would have otherwise caused type errors.
This rule optionally takes one argument, an object to configure which type warnings to enable. By default, all of the
warnings are enabled. e.g. to disable the any
warning (allowing it to exist in your code), while continuing to warn
about Object
and Function
:
{
"rules": {
"flowtype/no-weak-types": [2, {
"any": false,
"Object": true,
"Function": true
}]
}
}
// or, the following is equivalent as default is true:
{
"rules": {
"flowtype/no-weak-types": [2, {
"any": false
}]
}
}
The following patterns are considered problems:
function foo(thing): any {}
// Message: Unexpected use of weak type "any"
function foo(thing): Promise<any> {}
// Message: Unexpected use of weak type "any"
function foo(thing): Promise<Promise<any>> {}
// Message: Unexpected use of weak type "any"
function foo(thing): Object {}
// Message: Unexpected use of weak type "Object"
function foo(thing): Promise<Object> {}
// Message: Unexpected use of weak type "Object"
function foo(thing): Promise<Promise<Object>> {}
// Message: Unexpected use of weak type "Object"
function foo(thing): Function {}
// Message: Unexpected use of weak type "Function"
function foo(thing): Promise<Function> {}
// Message: Unexpected use of weak type "Function"
function foo(thing): Promise<Promise<Function>> {}
// Message: Unexpected use of weak type "Function"
(foo: any) => {}
// Message: Unexpected use of weak type "any"
(foo: Function) => {}
// Message: Unexpected use of weak type "Function"
(foo?: any) => {}
// Message: Unexpected use of weak type "any"
(foo?: Function) => {}
// Message: Unexpected use of weak type "Function"
(foo: { a: any }) => {}
// Message: Unexpected use of weak type "any"
(foo: { a: Object }) => {}
// Message: Unexpected use of weak type "Object"
(foo: any[]) => {}
// Message: Unexpected use of weak type "any"
type Foo = any
// Message: Unexpected use of weak type "any"
type Foo = Function
// Message: Unexpected use of weak type "Function"
type Foo = { a: any }
// Message: Unexpected use of weak type "any"
type Foo = { a: Object }
// Message: Unexpected use of weak type "Object"
type Foo = { (a: Object): string }
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