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type-annotation-spacing

danger
This rule will soon be moved to eslint-stylistic. See What About Formatting? for more information.

Require consistent spacing around type annotations.

🔧

Some problems reported by this rule are automatically fixable by the --fix ESLint command line option.

Spacing around type annotations improves readability of the code. Although the most commonly used style guideline for type annotations in TypeScript prescribes adding a space after the colon, but not before it, it is subjective to the preferences of a project. For example:

// with space after, but not before (default if no option is specified)
let foo: string = "bar";

// with no spaces
let foo:string = "bar";

// with space before and after
let foo : string = "bar";

// with space before, but not after
let foo :string = "bar";

// with spaces before and after the fat arrow (default if no option is specified)
type Foo = (string: name) => string;

// with no spaces between the fat arrow
type Foo = (string: name)=>string;

// with space after, but not before the fat arrow
type Foo = (string: name)=> string;

// with space before, but not after the fat arrow
type Foo = (string: name) =>string;
.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/type-annotation-spacing": "error"
  }
};
Try this rule in the playground ↗

Examples​

This rule aims to enforce specific spacing patterns around type annotations and function types in type literals.

let foo:string = "bar";
let foo :string = "bar";
let foo : string = "bar";

function foo():string {}
function foo() :string {}
function foo() : string {}

class Foo {
    name:string;
}

class Foo {
    name :string;
}

class Foo {
    name : string;
}

type Foo = ()=>{};
type Foo = () =>{};
type Foo = ()=> {};
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Options​

This rule accepts the following options

type SpacingConfig = {
  after?: boolean;
  before?: boolean;
};

type Options = [
  {
    after?: boolean;
    before?: boolean;
    overrides?: {
      arrow?: SpacingConfig;
      colon?: SpacingConfig;
      parameter?: SpacingConfig;
      property?: SpacingConfig;
      returnType?: SpacingConfig;
      variable?: SpacingConfig;
    };
  },
];

const defaultOptions: Options = [{}];

after​

{ "before": false, "after": true }
let foo:string = "bar";
let foo :string = "bar";
let foo : string = "bar";

function foo():string {}
function foo() :string {}
function foo() : string {}

class Foo {
    name:string;
}

class Foo {
    name :string;
}

class Foo {
    name : string;
}

type Foo = ()=>{};
type Foo = () =>{};
type Foo = () => {};
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before​

{ "before": true, "after": true }
let foo: string = "bar";
let foo:string = "bar";
let foo :string = "bar";

function foo(): string {}
function foo():string {}
function foo() :string {}

class Foo {
    name: string;
}

class Foo {
    name:string;
}

class Foo {
    name :string;
}

type Foo = ()=>{};
type Foo = () =>{};
type Foo = ()=> {};
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overrides - colon​

{
  "before": false,
  "after": false,
  "overrides": { "colon": { "before": true, "after": true } }
}
let foo: string = "bar";
let foo:string = "bar";
let foo :string = "bar";

function foo(): string {}
function foo():string {}
function foo() :string {}

class Foo {
    name: string;
}

class Foo {
    name:string;
}

class Foo {
    name :string;
}

type Foo = () =>{};
type Foo = ()=> {};
type Foo = () => {};
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overrides - arrow​

{
  "before": false,
  "after": false,
  "overrides": { "arrow": { "before": true, "after": true } }
}
let foo: string = "bar";
let foo : string = "bar";
let foo :string = "bar";

function foo(): string {}
function foo():string {}
function foo() :string {}

class Foo {
    name: string;
}

class Foo {
    name : string;
}

class Foo {
    name :string;
}

type Foo = ()=>{};
type Foo = () =>{};
type Foo = ()=> {};
Open in Playground

When Not To Use It​

If you don't want to enforce spacing for your type annotations, you can safely turn this rule off.

Further Reading​

Resources​