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@stylistic/ts/

type-annotation-spacing ​

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:

ts
// 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;
// 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;

Examples ​

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

❌ Incorrect ​

ts
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 = ()=> {};
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 = ()=> {};

✅ Correct ​

ts
let foo: string = "bar";

function foo(): string {}

class Foo {
    name: string;
}

type Foo = () => {};
let foo: string = "bar";

function foo(): string {}

class Foo {
    name: string;
}

type Foo = () => {};

Options ​

after ​

json
{ "before": false, "after": true }
{ "before": false, "after": true }

❌ Incorrect ​

ts
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 = () => {};
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 = () => {};

✅ Correct ​

ts
let foo: string = "bar";

function foo(): string {}

class Foo {
    name: string;
}

type Foo = ()=> {};
let foo: string = "bar";

function foo(): string {}

class Foo {
    name: string;
}

type Foo = ()=> {};

before ​

json
{ "before": true, "after": true }
{ "before": true, "after": true }

❌ Incorrect ​

ts
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 = ()=> {};
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 = ()=> {};

✅ Correct ​

ts
let foo : string = "bar";

function foo() : string {}

class Foo {
    name : string;
}

type Foo = () => {};
let foo : string = "bar";

function foo() : string {}

class Foo {
    name : string;
}

type Foo = () => {};

overrides - colon ​

json
{
  "before": false,
  "after": false,
  "overrides": { "colon": { "before": true, "after": true } }
}
{
  "before": false,
  "after": false,
  "overrides": { "colon": { "before": true, "after": true } }
}

❌ Incorrect ​

ts
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 = () => {};
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 = () => {};

✅ Correct ​

ts
let foo : string = "bar";

function foo() : string {}

class Foo {
    name : string;
}

type Foo = {
    name: (name : string)=>string;
}

type Foo = ()=>{};
let foo : string = "bar";

function foo() : string {}

class Foo {
    name : string;
}

type Foo = {
    name: (name : string)=>string;
}

type Foo = ()=>{};

overrides - arrow ​

json
{
  "before": false,
  "after": false,
  "overrides": { "arrow": { "before": true, "after": true } }
}
{
  "before": false,
  "after": false,
  "overrides": { "arrow": { "before": true, "after": true } }
}

❌ Incorrect ​

ts
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 = ()=> {};
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 = ()=> {};

✅ Correct ​

ts
let foo:string = "bar";

function foo():string {}

class Foo {
    name:string;
}

type Foo = () => {};
let foo:string = "bar";

function foo():string {}

class Foo {
    name:string;
}

type Foo = () => {};

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 ​

Released under the MIT License.

Copyright OpenJS Foundation and other contributors, www.openjsf.org.
Copyright © 2023-PRESENT ESLint Stylistic contributors.