Types Reference

License NPM Version Open Issues

🏷️ Collection of TypeScript types shared across Lou Codes projects.

Usage

📦 Node

Install @lou.codes/types as a dependency:

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pnpm add @lou.codes/types
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# or
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npm install @lou.codes/types
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# or
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yarn add @lou.codes/types

Import as type and use it:

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import type { Unary } from "@lou.codes/types";

🦕 Deno

Import @lou.codes/types using the npm: prefix, and use it directly:

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import type { Unary } from "npm:@lou.codes/types";

Useful links

📝 Documentation: TypeDoc generated documentation.
⏳ Changelog: List of changes between versions.

Array

ArrayLike<Item, Length>

1
type ArrayLike<Item, Length>: ReadOnlyRecord<NeverFallback<Exclude<Enumerate<Length>, Length>, number>, Item> & object;

An alternative for TypeScript’s ArrayLike type, with its type set to unknown by default. It also makes it shallowly read-only.

Remarks

When working with optional types, having to type ArrayLike<unknown> every time gets annoying pretty fast. This type is a drop-in replacement for ArrayLike, with the only difference being that the type of the items is set to unknown by default.

Example

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const arrayLike: ArrayLike<number> = [1, 2, 3];

Type declaration

Member	Type	Description
`length`	`Length`	Amount of items in the ArrayLike.

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the array-like object.
`Length` extends `number`	`number`	-

Empty

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type Empty: EmptyArray | EmptyRecord | EmptyString;

Empty array, object or string.

Remarks

Union type of EmptyArray, EmptyRecord and EmptyString, to signify values that are empty.

Example

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const emptyString: Empty = "";
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const emptyArray: Empty = [];
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const emptyRecord: Empty = {};

EmptyArray

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type EmptyArray: typeof EMPTY_ARRAY;

Empty array.

Remarks

This is a type alias for an readonly empty array. Trying to access items on it will give a compile-time error.

Example

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const emptyArray: EmptyArray = [];

Entry<Key, Value>

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type Entry<Key, Value>: readonly [Key, Value];

Entry couple [key, value].

Remarks

It is a tuple of two elements, the first one being the key and the second one being the value of an object’s property.

Example

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const entry: Entry<string, number> = ["🟢", 1];

Type parameters

Type parameter	Value	Description
`Key`	`PropertyKey`	Object’s properties type.
`Value`	`unknown`	Object’s values type.

EntryKey<Input>

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type EntryKey<Input>: Input[0];

Key of an Entry.

Remarks

Util type to get the key of an Entry.

Example

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const entry: Entry<string, number> = ["🟢", 1];
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const entryKey: EntryKey<typeof entry> = entry[0];

See

Entry

Type parameters

Type parameter	Description
`Input` extends `Entry`	Entry type.

EntryOf<Type>

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type EntryOf<Type>: Entry<KeyOf<Type>, ValueOf<Type>>;

Object or array Entry.

Remarks

Get the Entry type out of an object or array.

Example

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const object = {
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	"🟢": 1,
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	"🟩": 2,
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};
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const entries: EntryOf<typeof object> = Object.entries(object)[0];

See

Entry
KeyOf
ValueOf

Type parameters

Type parameter	Description
`Type` extends `object`	Object or array type.

EntryValue<Input>

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type EntryValue<Input>: Input[1];

Value of an Entry.

Remarks

Util type to get the value of an Entry.

Example

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const entry: Entry<string, number> = ["🟢", 1];
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const entryValue: EntryValue<typeof entry> = entry[1];

See

Entry

Type parameters

Type parameter	Description
`Input` extends `Entry`	Entry type.

Head<Input>

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type Head<Input>: HeadAndTail<Input>[0];

Initial value of an ArrayLike.

Remarks

Given a type argument (an ArrayLike), this returns the type of the item in index 0.

Example

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const array = ["🟢", "🟩", "💚"];
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const head: Head<typeof array> = "🟢";

See

ArrayLike
HeadAndTail

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	`ArrayLike` value (such as `Array` or `string`).

HeadAndTail<Input>

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type HeadAndTail<Input>: Input extends readonly [infer HeadItem, infer TailItems] ? readonly [HeadItem, TailItems] : Input extends `${infer FirstCharacter}${infer RestOfString}` ? readonly [FirstCharacter, RestOfString] : Input extends EmptyArray | EmptyString ? readonly [undefined, Input] : readonly [Maybe<Input[number]>, Input];

Get a couple with the head and tail types of an ArrayLike.

Remarks

Given a type argument (an ArrayLike), this returns a couple with the type of the item in index 0 first, and the rest of the ArrayLike after.

Example

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const array = ["🟢", "🟩", "💚"];
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const headAndTail: HeadAndTail<typeof array> = ["🟢", ["🟩", "💚"]];

See

ArrayLike
EmptyArray
EmptyString
Head
Maybe
Tail

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	Input `ArrayLike`.

Initial<Input>

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type Initial<Input>: InitialAndLast<Input>[0];

Initial values of an ArrayLike (omitting the last).

Remarks

Given a type argument (an ArrayLike), this returns the type of the items from the start of the ArrayLike until the before to last item.

Example

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const array = ["🟢", "🟩", "💚"];
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const initial: Initial<typeof array> = ["🟢", "🟩"];

See

ArrayLike
InitialAndLast

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	`ArrayLike` value (such as `Array` or `string`).

InitialAndLast<Input>

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type InitialAndLast<Input>: Input extends readonly [...(infer InitialItems), infer LastItem] ? readonly [InitialItems, LastItem] : Input extends EmptyArray | EmptyString ? readonly [Input, undefined] : Input extends `${infer FirstCharacter}${infer RestOfString}` ? readonly [`${RestOfString extends EmptyString ? EmptyString : FirstCharacter}${Head<InitialAndLast<RestOfString>>}`, `${RestOfString extends EmptyString ? FirstCharacter : Last<RestOfString>}`] : readonly [Input, Maybe<Input[number]>];

Get a couple with the initial and last types of an ArrayLike.

Remarks

Given a ArrayLike, this returns a couple with the type of all items from the start until the item before last, and then the last.

Example

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const array = ["🟢", "🟩", "💚"];
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const initialAndLast: InitialAndLast<typeof array> = [["🟢", "🟩"], "💚"];

See

ArrayLike
EmptyArray
EmptyString
Head
Initial
Last
Maybe

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	Input `ArrayLike`.

KeyOf<Type>

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type KeyOf<Type>: Type extends ArrayLike ? NeverFallback<Just<Exclude<Partial<Type>["length"], Type["length"]>>, number> : `${Exclude<keyof Type, symbol>}`;

Generic key for either object or array.

Remarks

Type to represent the type of the key in an array or object. It automatically omits symbol keys from objects, and uses number for arrays with dynamic length.

Example

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const array = [1, 2, 3] as const;
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const object = { "🟢": "🟩" } as const;
3

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const arrayKey: KeyOf<typeof array> = 0;
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const objectKey: KeyOf<typeof object> = "🟢";

Type parameters

Type parameter	Description
`Type` extends `object`	Object or array type.

Last<Input>

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type Last<Input>: InitialAndLast<Input>[1];

Last value of an ArrayLike.

Remarks

Type of the last character of a string or the last element of an array.

Example

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const array = ["🟢", "🟩", "💚"];
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const last: Last<typeof array> = "💚";

See

ArrayLike
InitialAndLast

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	The input `ArrayLike`.

MaybeEmpty<Input>

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type MaybeEmpty<Input>: Either<Input, Input extends ReadOnlyArray ? EmptyArray : Input extends string ? EmptyString : Input extends ReadOnlyRecord ? EmptyRecord : undefined>;

Creates an union of the given type with a possible “empty” value.

Remarks

This type is useful to make clear that we expect a possible empty value.

Example

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type Greet: MaybeEmpty<"Hello">; // "Hello" | ""
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type Triple: MaybeEmpty<readonly [1, 2, 3]>; // readonly [1, 2, 3] | readonly []
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type Foo: MaybeEmpty<{ readonly foo: "bar" }>; // { readonly foo: "bar" } | {}

See

Either
EmptyArray
EmptyRecord
EmptyString

Type parameters

Type parameter	Description
`Input`	Type to unite with it’s empty counterpart.

NotEmpty<Type>

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type NotEmpty<Type>: Exclude<Type, Empty>;

Type for a non-empty ArrayLike, object or string.

Remarks

This type is useful for cases where you want to ensure that a value is not empty. For example, if you have an array that should always have at least one element, you could type it as NotEmpty<ArrayLike<ElementType>>.

Example

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const notEmptyString: NotEmpty<string> = "🟢";
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const notEmptyArray: NotEmpty<ReadOnlyArray> = ["🟢", "🟩"];
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const notEmptyRecord: NotEmpty<ReadOnlyRecord> = { "🟢": "🟩" };

See

Empty

Type parameters

Type parameter	Description
`Type` extends `ArrayLike` \| `object` \| `string`	The type to check.

ReadOnlyArray<Item>

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type ReadOnlyArray<Item>: ReadonlyArray<Item>;

An alternative for TypeScript’s ReadonlyArray type, with its type set to unknown by default.

Remarks

There’s already a native ReadonlyArray type, but this type has a default type parameter to make it easier to use when the type of an array is unknown.

Example

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const array: ReadOnlyArray<{ "🟢": number }> = [{ "🟢": 1 }, { "🟢": 2 }];
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array[0]["🟢"] = 3; // Error

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the array.

Reducer<Item, Accumulator>

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type Reducer<Item, Accumulator>: Unary<Item, Unary<Accumulator, Accumulator>>;

Reducer/Folder function.

Remarks

Type to represent a folder/reducer unary function that takes an item and an accumulator something of the type of the accumulator.

Example

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const reducer: Reducer<number, number> = item => accumulator =>
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	accumulator + item;

See

Unary

Type parameters

Type parameter	Description
`Item`	Type of the items to reduce.
`Accumulator`	Type of the accumulator/output.

Tail<Input>

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type Tail<Input>: HeadAndTail<Input>[1];

Last values of an ArrayLike (omitting the first).

Remarks

Type of the last items of an ArrayLike, excluding the first item in said ArrayLike.

Example

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const array = ["🟢", "🟩", "💚"];
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const tail: Tail<typeof array> = ["🟩", "💚"];

See

ArrayLike
HeadAndTail

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	Type of the array to get the tail.

ValueOf<Type>

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type ValueOf<Type>: KeyOf<Type> extends keyof Type ? Type[KeyOf<Type>] : never;

Generic key for either object or array.

Remarks

This type is used to get the type of the values in a collection (items of an ArrayLike or properties of a Record).

Example

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const object = {
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	"🟢": 1,
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	"🟩": 2,
4
};
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const key: ValueOf<typeof object> = 1;

See

KeyOf

Type parameters

Type parameter	Description
`Type` extends `object`	Object or array type.

Common

Awaitable<Type>

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type Awaitable<Type>: PromiseLike<Type> | Type;

A value that might be coming from a Promise.

Remarks

Union type useful when you want to accept both Promise and non-Promise for a given type, both “awaitable”.

Example

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type AwaitableString = Awaitable<string>;
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const promisedValue: AwaitableString = Promise.resolve("🟢");
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const plainValue: AwaitableString = "🟩";
4

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Promise.all([promisedValue, plainValue]).then(console.log); // ["🟢", "🟩"]

See

Promise

Type parameters

Type parameter	Value	Description
`Type`	`unknown`	The type to await.

Either<Right, Left>

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type Either<Right, Left>: Left | Right;

Value that can be something or something else.

Remarks

Union type useful for cases where a value might be of one type or another. By convention we use Right for the “success” type and Left for the error.

Example

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type MaybeNumber = Either<number, string>;
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const maybeNumber: MaybeNumber = 1;
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const notNumber: MaybeNumber = "1";

Type parameters

Type parameter	Description
`Right`	The “correct” type.
`Left`	The “error” type.

Falsy

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type Falsy:
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  | EmptyString
3
  | HTMLAllCollection
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  | Nullish
5
  | 0
6
  | 0n
7
  | false;

Types that evaluates to false in JS.

Remarks

Union type of the values that evaluate to false in JavaScript. Due to TypeScript type limitations NaN can’t be included.

Example

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const falsyBoolean: Falsy = false;
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const falsyHTMLAllCollection: Falsy = document.all;
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const falsyNegativeZero: Falsy = -0;
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const falsyNegativeZeroBigInt: Falsy = -0n;
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const falsyNull: Falsy = null;
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const falsyString: Falsy = "";
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const falsyUndefined: Falsy = undefined;
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const falsyZero: Falsy = 0;
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const falsyZeroBigInt: Falsy = 0n;

See

JSONValue

1
type JSONValue: Exclude<Primitive, bigint | symbol | undefined> | ReadonlyArray<JSONValue> | object;

Possible parsed JSON value.

Remarks

Following the JSON specification, the result of a JSON.parse call can be one of a given set of types. This type is a union of all of those types.

Example

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const json: JSONValue = JSON.parse('{"foo": "bar"}');

See

JSON

Just<Input>

1
type Just<Input>: Exclude<Input, undefined>;

Excludes undefined of a type union.

Remarks

Every now and then a type is possibly undefined, this type gets rid of the undefined in the union.

Example

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const maybeUndefined: string | undefined = "🟢";
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const defined: Just<typeof maybeUndefined> = "🟢"; // ok
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const noDefined: Just<typeof maybeUndefined> = undefined; // error

See

Maybe

Type parameters

Type parameter
`Input`

Maybe<Input>

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type Maybe<Input>: Either<Just<Input>, undefined>;

Value that can be undefined.

Remarks

Union type useful for cases where a value might be undefined, and provides a simple way to express this in TypeScript. For example, the return type of a function that returns a string or undefined could be typed as Maybe<string>.

Example

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type MaybeNumber = Maybe<number>;
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const maybeNumber: MaybeNumber = 1;
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const notNumber: MaybeNumber = undefined;

See

Just

Type parameters

Type parameter	Description
`Input`	The type of the value to make optional.

NeverFallback<MaybeNever, Fallback>

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type NeverFallback<MaybeNever, Fallback>: Single<MaybeNever> extends Single<never> ? Fallback : MaybeNever;

Takes a value that could be never, and if it is never it goes to the Fallback value.

Remarks

There are some scenarios where a value can end up being of type never, this works sorta like the the ?? operator, but for never.

Example

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const value: never = undefined as never;
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NeverFallback<typeof value, number>; // Will be number

See

Single

Type parameters

Type parameter	Description
`MaybeNever`	The type that may or may not be `never`.
`Fallback`	The fallback type to use if `MaybeNever` is `never`.

Nullish

1
type Nullish: Maybe<null>;

Nullish value (either null or undefined).

Remarks

This type is useful for cases where a value might be null or undefined, generally meant to be dealt with using the ?? operator.

Example

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const nullishUndefined: Nullish = undefined;
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const nullishNull: Nullish = null;

See

Primitive

1
type Primitive:
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  | Nullish
3
  | Numeric
4
  | boolean
5
  | string
6
  | symbol;

Valid JavaScript primitives.

Remarks

This type is a union of all the valid JavaScript primitives, including null, undefined, boolean, number, bigint, string, and symbol.

Example

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const aBigInt: Primitive = 13n;
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const aBoolean: Primitive = true;
3
const aNull: Primitive = null;
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const aNumber: Primitive = 13;
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const anUndefined: Primitive = undefined;
6
const aString: Primitive = "🟢";
7
const aSymbol: Primitive = Symbol("🟢");

See

Nullish
Numeric
Primitive

Replace<Type, Keys, NewType>

1
type Replace<Type, Keys, NewType>: Omit<Type, Keys> & { readonly [Property in Keys]: NewType };

Intersection that replaces the type of some keys in given object type.

Remarks

Intersection type to replace all the given keys of an object type with a new type.

Example

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type User = { name: string; age: number };
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type ReallyOldUser = Replace<User, "age", bigint>;

Type parameters

Type parameter	Description
`Type` extends `object`	Type to replace the type of some keys in.
`Keys` extends keyof `Type`	Keys to replace the type of.
`NewType`	New type to replace the old type with.

Single<Type>

1
type Single<Type>: readonly [Type];

Tuple of length 1 (AKA Monuple).

Remarks

Tuple with a single element on it, useful when doing optional types that compare to never.

Example

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const single: Single<boolean> = [true];

Type parameters

Type parameter	Description
`Type`	Type of the single element.

Strigifiable

1
type Strigifiable: Exclude<Primitive, symbol>;

Values that can be stringified.

Remarks

Type to represent all values that can be stringified, all primitives excluding symbol: string, number, bigint, boolean, undefined, and null.

Example

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let value: Strigifiable = "hello";
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value = 1;
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value = true;
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value = Symbol("hello"); // Error!
5
value = { toString: () => "hello" }; // Error!

See

Primitive

Truthy<Type>

1
type Truthy<Type>: Exclude<Type, Falsy>;

Excludes all Falsy values of the given Type.

Remarks

Type to represent all values of the given Type that are not Falsy. If all types are Falsy, the result is never.

Example

1
Truthy<"" | "truthy">; // "truthy"

See

Falsy

Type parameters

Type parameter	Value	Description
`Type`	`unknown`	Type to exclude `Falsy` values from.

TypeOfDictionary

1
type TypeOfDictionary: object;

typeof dictionary.

Remarks

Dictionary of types and their typeof values, including the proposed but never added type "null" for null.

Example

1
TypeOfMap["string"]; // `string`
2
TypeOfMap["boolean"]; // `boolean`
3
TypeOfMap["function"]; // `GenericFunction`

See

Type declaration

Member	Type	Description
`bigint`	`bigint`	TypeOfDictionary key for `BigInt`
`boolean`	`boolean`	TypeOfDictionary key for `Boolean`
`function`	`Function`	TypeOfDictionary key for `Function`
`null`	`null`	TypeOfDictionary key for `null`
`number`	`number`	TypeOfDictionary key for `Number`
`object`	`object`	TypeOfDictionary key for `Object`
`string`	`string`	TypeOfDictionary key for `String`
`symbol`	`symbol`	TypeOfDictionary key for `Symbol`
`undefined`	`undefined`	TypeOfDictionary key for `undefined`

TypeOfValue

1
type TypeOfValue: KeyOf<TypeOfDictionary>;

Possible type values returned by typeof.

Remarks

Type to represent the possible values returned by typeof, including the proposed but never added type "null" for null.

Example

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const typeString: TyeOfValue = "string";
2
const typeBoolean: TyeOfValue = "boolean";
3
const typeFunction: TyeOfValue = "function";

See

Date

DayOfMonth

1
type DayOfMonth: Range<1, 31>;

Day of the month values in numeric format (from 1 to 31).

Remarks

Stricter than number type for day of the month values, limited to valid values from 1 to 31, and giving type errors otherwise.

Example

1
const days: Iterable<DayOfMonth> = [1, 2, 3, 28, 29, 30, 31];

See

Enumerate
Date

DayOfWeek

1
type DayOfWeek: Enumerate<6>;

Day of the week values in numeric format (from 0 to 6).

Remarks

Stricter than number type for day of the week values, limited to valid values from 0 to 6, and giving type errors otherwise.

Example

1
const daysOfWeek: Iterable<DayOfWeek> = [0, 1, 2, 3, 4, 5, 6];

See

Enumerate
Date

Hours

1
type Hours: Enumerate<23>;

Hours values in numeric format (from 0 to 23).

Remarks

Stricter than number type for hour values, limited to valid values from 0 to 23, and giving type errors otherwise.

Example

1
const hours: Iterable<Hours> = [0, 1, 2, 3, 20, 21, 22, 23];

See

Enumerate
Date

ISODate

1
type ISODate: `${ISOYear}-${ISOMonth}-${ISODayOfMonth}T${MultiDigitNumberString}:${MultiDigitNumberString}:${MultiDigitNumberString}.${MultiDigitNumberString}Z`;

String representing an ISO date.

Remarks

This type is a string representing an ISO 8601 format of a date (returned by Date#toISOString). It uses MultiDigitNumberString because the type complexity using better types is too hight.

Example

1
const date: ISODate = "2020-01-01T00:00:00.000Z";

See

ISODayOfMonth

1
type ISODayOfMonth: `${1 | 2}${Digit}` | `0${Exclude<Digit, 0>}` | `3${Enumerate<1>}`;

Day of the month values in string format ("01" to "31").

Remarks

Union type stricter than string type for day of the month values, limited to valid values from "01" to "31", and giving type errors otherwise.

Example

1
const days: Iterable<ISODayOfMonth> = ["01", "15", "31"];

See

Digit
Enumerate
Date

ISOHours

1
type ISOHours: `${Enumerate<1>}${Digit}` | `2${Enumerate<3>}`;

Hours values in string format (from "00" to "23").

Remarks

Union type stricter than string type for hour values, limited to valid values from "00" to "23", and giving type errors otherwise.

Example

1
const hours: Iterable<ISOHours> = ["00", "06", "23"];

See

Enumerate
Date

ISOMilliseconds

1
type ISOMilliseconds: `${Digit}${Digit}${Digit}`;

ISO milliseconds values in string format (from "000" to "999").

Remarks

Stricter than string type for millisecond values, limited to valid values from "000" to "999", and giving type errors otherwise.

Example

1
const milliseconds: Iterable<ISOMilliseconds> = ["001", "250", "999"];

See

Date
Digit

ISOMinutes

1
type ISOMinutes: `${Enumerate<5>}${Digit}`;

ISO minutes values in string format (from "00" to "59").

Remarks

Stricter than string type for minute values, limited to valid values from "00" to "59", and giving type errors otherwise.

Example

1
const minutes: Iterable<ISOMinutes> = ["00", "30", "59"];

See

Date
Digit
Enumerate

ISOMonth

1
type ISOMonth: `0${Exclude<Digit, 0>}` | `1${Enumerate<2>}`;

ISO Month values in string format (from "01" to "12").

Remarks

Union type stricter than string type for month values, limited to valid values from "01" to "12", and giving type errors otherwise.

Example

1
const months: Iterable<ISOMonth> = ["01", "06", "12"];

See

Date
Digit
Enumerate

ISOSeconds

1
type ISOSeconds: `${Enumerate<5>}${Digit}`;

ISO seconds values in string format (from "00" to "59").

Remarks

Stricter than string type for seconds values, limited to valid values from "00" to "59", and giving type errors otherwise.

Example

1
const seconds: Iterable<ISOSeconds> = ["00", "30", "59"];

See

Date
Digit
Enumerate

ISOYear

1
type ISOYear: `${EmptyString | "-00"}${MultiDigitNumberString}`;

ISO year values in string format.

Remarks

Stricter than string type for year values, limited to valid values from "-271821" to "275760", and giving type errors otherwise.

Example

1
const years: Iterable<ISOYear> = ["2020", "-001000", "1989"];

See

Date

Milliseconds

1
type Milliseconds: Enumerate<999>;

ISO milliseconds values in number format (from 0 to 999).

Remarks

Stricter than number type for millisecond values, limited to valid values from 0 to 999, and giving type errors otherwise.

Example

1
const milliseconds: Iterable<Milliseconds> = [1, 250, 999];

See

Date
Enumerate

Minutes

1
type Minutes: Enumerate<59>;

ISO minutes values in number format (from 0 to 59).

Remarks

Stricter than number type for minute values, limited to valid values from 0 to 59, and giving type errors otherwise.

Example

1
const minutes: Iterable<Minutes> = [0, 30, 59];

See

Date
Enumerate

Month

1
type Month: Enumerate<11>;

ISO Month values in number format (from 0 to 11).

Remarks

Stricter than number type for month values, limited to valid values from 0 to 11, and giving type errors otherwise.

Example

1
const months: Iterable<ISOMonth> = [1, 6, 11];

See

Date
Enumerate

Seconds

1
type Seconds: Enumerate<59>;

ISO seconds values in number format (from 0 to 59).

Remarks

Stricter than number type for seconds values, limited to valid values from 0 to 59, and giving type errors otherwise.

Example

1
const seconds: Iterable<Seconds> = [0, 30, 59];

See

Date
Enumerate

Function

Class()<Arguments, Instance>

1
type Class<Arguments, Instance>: (...constructorArguments: Arguments) => Instance;

A generic type for classes.

Remarks

This type is a generic constructor function, mainly used when wrapping classes.

Example

1
const example = (AClass: Class) => new AClass("test");

See

ReadOnlyArray

Type parameters

Type parameter	Value	Description
`Arguments` extends `ReadOnlyArray`	`ReadOnlyArray`	Arguments of the class constructor.
`Instance`	`unknown`	Instance of the class.

Parameters

Parameter	Type
…`constructorArguments`	`Arguments`

Returns

Instance

Filter<Input>

1
type Filter<Input>: Unary<Input, boolean>;

Unary function that returns a boolean.

Remarks

This type is useful for cases where a function needs to check if a certain condition holds for an input value.

Example

1
const isEven: Filter<number> = number => number % 2 === 0;

See

Param

The input value to check.

Type parameters

Type parameter	Description
`Input`	The type of the input value.

Predicate()<Input, Predicated>

1
type Predicate<Input, Predicated>: (input: Input) => input is Predicated;

Unary function that returns a boolean and infers a given type for its argument.

Remarks

This type is useful for cases where a function needs to check if a certain condition holds for an input value. For example, the type of a filtering function that filters strings in an array of strings and numbers could look like Predicate<string | number, string>.

Example

1
const isString: Predicate<number | string, string> = (
2
	numberOrString,
3
): numberOrString is string => typeof numberOrString === "string";

Type parameters

Type parameter	Value	Description
`Input`	-	The type of the input value.
`Predicated` extends `Input`	`Input`	The subset of `Input` for which the predicate holds.

Parameters

Parameter	Type	Description
`input`	`Input`	The input value to check.

Returns

input is Predicated

ReadOnlyArguments<Input>

1
type ReadOnlyArguments<Input>: Input extends (..._arguments: infer Arguments) => infer _Output ? Readonly<Arguments> : never;

Read-only alternative to TypeScript’s Parameters

Remarks

This type extracts the parameters of a function as a read-only tuple, similar to Parameters, but with the added benefit of making the parameters read-only.

Example

1
const example = (_foo: string, _bar: number) => undefined;
2
type ExampleArguments = ReadOnlyArguments<typeof example>; // readonly [string, number]

See

Function
ReadOnlyArray

Type parameters

Type parameter	Description
`Input` extends `Function`	Function to extract parameters from.

Reducer<Item, Accumulator>

1
type Reducer<Item, Accumulator>: Unary<Item, Unary<Accumulator, Accumulator>>;

Reducer/Folder function.

Remarks

Type to represent a folder/reducer unary function that takes an item and an accumulator something of the type of the accumulator.

Example

1
const reducer: Reducer<number, number> = item => accumulator =>
2
	accumulator + item;

See

Unary

Type parameters

Type parameter	Description
`Item`	Type of the items to reduce.
`Accumulator`	Type of the accumulator/output.

Tagger()<Output, Expressions>

1
type Tagger<Output, Expressions>: (templateStrings: TemplateStringsArray, ...expressions: Expressions) => Output;

Tag function for tagged templates.

Remarks

Type to represent a tag function for tagged templates, which takes a TemplateStringArray and any number of expressions, and returns a value of type Output (string by default).

Example

1
const intParser: Tagger<number> = strings => parseInt(strings.join(""), 10);
2
intParser`100`; // 100

See

ReadOnlyArray

Type parameters

Type parameter	Value	Description
`Output`	`string`	Type of the output value.
`Expressions` extends `ReadOnlyArray`	`ReadOnlyArray`	Type of the expressions.

Parameters

Parameter	Type
`templateStrings`	`TemplateStringsArray`
…`expressions`	`Expressions`

Returns

Output

Unary()<Input, Output>

1
type Unary<Input, Output>: (input: Input) => Output;

Unary function.

Remarks

Type to represent a function that takes a single argument, ideal for currying.

Example

1
const unary: Unary<number, number> = number => number + 1;

See

Function
Single

Type parameters

Type parameter	Description
`Input`	Type of the input value.
`Output`	Type of the output value.

Parameters

Parameter	Type
`input`	`Input`

Returns

Output

UnaryInput<UnaryFunction>

1
type UnaryInput<UnaryFunction>: UnaryFunction extends Unary<infer Input, infer _Output> ? Input : never;

Unary function input type.

Remarks

This type is used to get the input type of a Unary function.

Example

1
const unary: Unary<number, string> = number => `${number}`;
2
UnaryInput<typeof unary>; // `number`

See

Unary

Type parameters

Type parameter	Description
`UnaryFunction` extends `Unary`<`never`, `unknown`>	Type of the unary function to get the input type of.

UnaryOutput<UnaryFunction>

1
type UnaryOutput<UnaryFunction>: UnaryFunction extends Unary<infer _Input, infer Output> ? Output : never;

Unary function output type.

Remarks

This type is used to get the output type of a Unary function.

Example

1
const unary: Unary<number, string> = number => `${number}`;
2
UnaryOutput<typeof unary>; // `string`

See

Unary

Type parameters

Type parameter	Description
`UnaryFunction` extends `Unary`<`never`, `unknown`>	Type of the unary function to get the output type of.

HTML

HTMLElementTagAttributeMap

1
type HTMLElementTagAttributeMap: ReadOnlyRecord<`${string}-${string}`, HTMLElementTagGlobalAttributes> & object;

Map of HTML element tag attributes.

Remarks

If you need the type of the HTML attributes of an HTML element, this is it.

Example

1
const getAttribute =
2
	<Tag extends keyof HTMLElementTagAttributeMap>(tag: Tag) =>
3
	(attribute: keyof HTMLElementTagAttributeMap[Tag]) => // …

See

HTMLElementTagGlobalAttributes
ReadOnlyRecord

Type declaration

Member	Type	Description
`a`	`HTMLElementTagGlobalAttributes` & `object`	If the a element has an href attribute, then it represents a hyperlink (a hypertext anchor) labeled by its contents. --- References See MDN Reference
`abbr`	`HTMLElementTagGlobalAttributes`	The abbr element represents an abbreviation or acronym, optionally with its expansion. The title attribute may be used to provide an expansion of the abbreviation. The attribute, if specified, must contain an expansion of the abbreviation, and nothing else. --- References See MDN Reference
`address`	`HTMLElementTagGlobalAttributes`	The address element represents the contact information for its nearest article or body element ancestor. If that is the body element, then the contact information applies to the document as a whole. --- References See MDN Reference
`area`	`HTMLElementTagGlobalAttributes` & `object`	The area element represents either a hyperlink with some text and a corresponding area on an image map, or a dead area on an image map. --- References See MDN Reference
`article`	`HTMLElementTagGlobalAttributes`	The article element represents a complete, or self-contained, composition in a document, page, application, or site and that is, in principle, independently distributable or reusable, e.g. in syndication. This could be a forum post, a magazine or newspaper article, a blog entry, a user-submitted comment, an interactive widget or gadget, or any other independent item of content. Each article should be identified, typically by including a heading (h1–h6 element) as a child of the article element. --- References See MDN Reference
`aside`	`HTMLElementTagGlobalAttributes`	The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography. --- References See MDN Reference
`audio`	`HTMLElementTagGlobalAttributes` & `object`	An audio element represents a sound or audio stream. --- References See MDN Reference
`b`	`HTMLElementTagGlobalAttributes`	The b element represents a span of text to which attention is being drawn for utilitarian purposes without conveying any extra importance and with no implication of an alternate voice or mood, such as key words in a document abstract, product names in a review, actionable words in interactive text-driven software, or an article lede. --- References See MDN Reference
`base`	`HTMLElementTagGlobalAttributes` & `object`	The base element allows authors to specify the document base URL for the purposes of resolving relative URLs, and the name of the default browsing context for the purposes of following hyperlinks. The element does not represent any content beyond this information. --- References See MDN Reference
`bdi`	`HTMLElementTagGlobalAttributes`	The bdi element represents a span of text that is to be isolated from its surroundings for the purposes of bidirectional text formatting. [BIDI] --- References See MDN Reference
`bdo`	`HTMLElementTagGlobalAttributes` & `object`	The bdo element represents explicit text directionality formatting control for its children. It allows authors to override the Unicode bidirectional algorithm by explicitly specifying a direction override. [BIDI] --- References See MDN Reference
`blockquote`	`HTMLElementTagGlobalAttributes` & `object`	The blockquote element represents content that is quoted from another source, optionally with a citation which must be within a footer or cite element, and optionally with in-line changes such as annotations and abbreviations. --- References See MDN Reference
`body`	`HTMLElementTagGlobalAttributes` & `object`	The body element represents the content of the document. --- References See MDN Reference
`br`	`HTMLElementTagGlobalAttributes` & `object`	The br element represents a line break. --- References See MDN Reference
`button`	`HTMLElementTagGlobalAttributes` & `object`	The button element represents a button labeled by its contents. --- References See MDN Reference
`canvas`	`HTMLElementTagGlobalAttributes` & `object`	The canvas element provides scripts with a resolution-dependent bitmap canvas, which can be used for rendering graphs, game graphics, art, or other visual images on the fly. --- References See MDN Reference
`caption`	`HTMLElementTagGlobalAttributes` & `object`	The caption element represents the title of the table that is its parent, if it has a parent and that is a table element. --- References See MDN Reference
`cite`	`HTMLElementTagGlobalAttributes`	The cite element represents a reference to a creative work. It must include the title of the work or the name of the author(person, people or organization) or an URL reference, or a reference in abbreviated form as per the conventions used for the addition of citation metadata. --- References See MDN Reference
`code`	`HTMLElementTagGlobalAttributes`	The code element represents a fragment of computer code. This could be an XML element name, a file name, a computer program, or any other string that a computer would recognize. --- References See MDN Reference
`col`	`HTMLElementTagGlobalAttributes` & `object`	If a col element has a parent and that is a colgroup element that itself has a parent that is a table element, then the col element represents one or more columns in the column group represented by that colgroup. --- References See MDN Reference
`colgroup`	`HTMLElementTagGlobalAttributes` & `object`	The colgroup element represents a group of one or more columns in the table that is its parent, if it has a parent and that is a table element. --- References See MDN Reference
`data`	`HTMLElementTagGlobalAttributes` & `object`	The data element links a given piece of content with a machine-readable translation. --- References See MDN Reference
`datalist`	`HTMLElementTagGlobalAttributes`	The datalist element represents a set of option elements that represent predefined options for other controls. In the rendering, the datalist element represents nothing and it, along with its children, should be hidden. --- References See MDN Reference
`dd`	`HTMLElementTagGlobalAttributes` & `object`	The dd element represents the description, definition, or value, part of a term-description group in a description list (dl element). --- References See MDN Reference
`del`	`HTMLElementTagGlobalAttributes` & `object`	The del element represents a removal from the document. --- References See MDN Reference
`details`	`HTMLElementTagGlobalAttributes` & `object`	The details element represents a disclosure widget from which the user can obtain additional information or controls. --- References See MDN Reference
`dfn`	`HTMLElementTagGlobalAttributes`	The dfn element represents the defining instance of a term. The paragraph, description list group, or section that is the nearest ancestor of the dfn element must also contain the definition(s) for the term given by the dfn element. --- References See MDN Reference
`dialog`	`HTMLElementTagGlobalAttributes` & `object`	The dialog element represents a part of an application that a user interacts with to perform a task, for example a dialog box, inspector, or window. --- References See MDN Reference
`div`	`HTMLElementTagGlobalAttributes`	The div element has no special meaning at all. It represents its children. It can be used with the class, lang, and title attributes to mark up semantics common to a group of consecutive elements. --- References See MDN Reference
`dl`	`HTMLElementTagGlobalAttributes`	The dl element represents an association list consisting of zero or more name-value groups (a description list). A name-value group consists of one or more names (dt elements) followed by one or more values (dd elements), ignoring any nodes other than dt and dd elements. Within a single dl element, there should not be more than one dt element for each name. --- References See MDN Reference
`dt`	`HTMLElementTagGlobalAttributes`	The dt element represents the term, or name, part of a term-description group in a description list (dl element). --- References See MDN Reference
`em`	`HTMLElementTagGlobalAttributes`	The em element represents stress emphasis of its contents. --- References See MDN Reference
`embed`	`HTMLElementTagGlobalAttributes` & `object`	The embed element provides an integration point for an external (typically non-HTML) application or interactive content. --- References See MDN Reference
`fieldset`	`HTMLElementTagGlobalAttributes` & `object`	The fieldset element represents a set of form controls optionally grouped under a common name. --- References See MDN Reference
`figcaption`	`HTMLElementTagGlobalAttributes`	The figcaption element represents a caption or legend for the rest of the contents of the figcaption element’s parent figure element, if any. --- References See MDN Reference
`figure`	`HTMLElementTagGlobalAttributes`	The figure element represents some flow content, optionally with a caption, that is self-contained (like a complete sentence) and is typically referenced as a single unit from the main flow of the document. --- References See MDN Reference
`footer`	`HTMLElementTagGlobalAttributes`	The footer element represents a footer for its nearest ancestor sectioning content or sectioning root element. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like. --- References See MDN Reference
`form`	`HTMLElementTagGlobalAttributes` & `object`	The form element represents a collection of form-associated elements, some of which can represent editable values that can be submitted to a server for processing. --- References See MDN Reference
`h1`	`HTMLElementTagGlobalAttributes`	The h1 element represents a section heading. --- References See MDN Reference
`h2`	`HTMLElementTagGlobalAttributes`	The h2 element represents a section heading. --- References See MDN Reference
`h3`	`HTMLElementTagGlobalAttributes`	The h3 element represents a section heading. --- References See MDN Reference
`h4`	`HTMLElementTagGlobalAttributes`	The h4 element represents a section heading. --- References See MDN Reference
`h5`	`HTMLElementTagGlobalAttributes`	The h5 element represents a section heading. --- References See MDN Reference
`h6`	`HTMLElementTagGlobalAttributes`	The h6 element represents a section heading. --- References See MDN Reference
`head`	`HTMLElementTagGlobalAttributes` & `object`	The head element represents a collection of metadata for the Document. --- References See MDN Reference
`header`	`HTMLElementTagGlobalAttributes`	The header element represents introductory content for its nearest ancestor sectioning content or sectioning root element. A header typically contains a group of introductory or navigational aids. When the nearest ancestor sectioning content or sectioning root element is the body element, then it applies to the whole page. --- References See MDN Reference
`hgroup`	`HTMLElementTagGlobalAttributes`	The hgroup element represents a heading and related content. It groups a single h1–h6 element with one or more p. --- References See MDN Reference
`hr`	`HTMLElementTagGlobalAttributes` & `object`	The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book. --- References See MDN Reference
`html`	`HTMLElementTagGlobalAttributes` & `object`	The html element represents the root of an HTML document. --- References See MDN Reference
`i`	`HTMLElementTagGlobalAttributes`	The i element represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose in a manner indicating a different quality of text, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, transliteration, a thought, or a ship name in Western texts. --- References See MDN Reference
`iframe`	`HTMLElementTagGlobalAttributes` & `object`	The iframe element represents a nested browsing context. --- References See MDN Reference
`img`	`HTMLElementTagGlobalAttributes` & `object`	An img element represents an image. --- References See MDN Reference
`input`	`HTMLElementTagGlobalAttributes` & `object`	The input element represents a typed data field, usually with a form control to allow the user to edit the data. --- References See MDN Reference
`ins`	`HTMLElementTagGlobalAttributes` & `object`	The ins element represents an addition to the document. --- References See MDN Reference
`kbd`	`HTMLElementTagGlobalAttributes`	The kbd element represents user input (typically keyboard input, although it may also be used to represent other input, such as voice commands). --- References See MDN Reference
`label`	`HTMLElementTagGlobalAttributes` & `object`	The label element represents a caption in a user interface. The caption can be associated with a specific form control, known as the label element’s labeled control, either using the for attribute, or by putting the form control inside the label element itself. --- References See MDN Reference
`legend`	`HTMLElementTagGlobalAttributes`	The legend element represents a caption for the rest of the contents of the legend element’s parent fieldset element, if any. --- References See MDN Reference
`li`	`HTMLElementTagGlobalAttributes` & `object`	The li element represents a list item. If its parent element is an ol, ul, or menu element, then the element is an item of the parent element’s list, as defined for those elements. Otherwise, the list item has no defined list-related relationship to any other li element. --- References See MDN Reference
`link`	`HTMLElementTagGlobalAttributes` & `object`	The link element allows authors to link their document to other resources. --- References See MDN Reference
`main`	`HTMLElementTagGlobalAttributes`	The main element represents the main content of the body of a document or application. The main content area consists of content that is directly related to or expands upon the central topic of a document or central functionality of an application. --- References See MDN Reference
`map`	`HTMLElementTagGlobalAttributes` & `object`	The map element, in conjunction with an img element and any area element descendants, defines an image map. The element represents its children. --- References See MDN Reference
`mark`	`HTMLElementTagGlobalAttributes`	The mark element represents a run of text in one document marked or highlighted for reference purposes, due to its relevance in another context. When used in a quotation or other block of text referred to from the prose, it indicates a highlight that was not originally present but which has been added to bring the reader’s attention to a part of the text that might not have been considered important by the original author when the block was originally written, but which is now under previously unexpected scrutiny. When used in the main prose of a document, it indicates a part of the document that has been highlighted due to its likely relevance to the user’s current activity. --- References See MDN Reference
`menu`	`HTMLElementTagGlobalAttributes`	The menu element represents an unordered list of interactive items. --- References See MDN Reference
`meta`	`HTMLElementTagGlobalAttributes` & `object`	The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements. --- References See MDN Reference
`meter`	`HTMLElementTagGlobalAttributes` & `object`	The meter element represents a scalar measurement within a known range, or a fractional value; for example disk usage, the relevance of a query result, or the fraction of a voting population to have selected a particular candidate. --- References See MDN Reference
`nav`	`HTMLElementTagGlobalAttributes`	The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links. --- References See MDN Reference
`noscript`	`HTMLElementTagGlobalAttributes`	The noscript element represents nothing if scripting is enabled, and represents its children if scripting is disabled. It is used to present different markup to user agents that support scripting and those that don’t support scripting, by affecting how the document is parsed. --- References See MDN Reference
`object`	`HTMLElementTagGlobalAttributes` & `object`	The object element can represent an external resource, which, depending on the type of the resource, will either be treated as an image, as a nested browsing context, or as an external resource to be processed by a plugin. --- References See MDN Reference
`ol`	`HTMLElementTagGlobalAttributes` & `object`	The ol element represents a list of items, where the items have been intentionally ordered, such that changing the order would change the meaning of the document. --- References See MDN Reference
`optgroup`	`HTMLElementTagGlobalAttributes` & `object`	The optgroup element represents a group of option elements with a common label. --- References See MDN Reference
`option`	`HTMLElementTagGlobalAttributes` & `object`	The option element represents an option in a select element or as part of a list of suggestions in a datalist element. --- References See MDN Reference
`output`	`HTMLElementTagGlobalAttributes` & `object`	The output element represents the result of a calculation performed by the application, or the result of a user action. --- References See MDN Reference
`p`	`HTMLElementTagGlobalAttributes`	The p element represents a paragraph. --- References See MDN Reference
`param`	`HTMLElementTagGlobalAttributes` & `object`	The param element defines parameters for plugins invoked by object elements. It does not represent anything on its own. --- References See MDN Reference
`picture`	`HTMLElementTagGlobalAttributes`	The picture element is a container which provides multiple sources to its contained img element to allow authors to declaratively control or give hints to the user agent about which image resource to use, based on the screen pixel density, viewport size, image format, and other factors. It represents its children. --- References See MDN Reference
`pre`	`HTMLElementTagGlobalAttributes` & `object`	The pre element represents a block of preformatted text, in which structure is represented by typographic conventions rather than by elements. --- References See MDN Reference
`progress`	`HTMLElementTagGlobalAttributes` & `object`	The progress element represents the completion progress of a task. The progress is either indeterminate, indicating that progress is being made but that it is not clear how much more work remains to be done before the task is complete (e.g. because the task is waiting for a remote host to respond), or the progress is a number in the range zero to a maximum, giving the fraction of work that has so far been completed. --- References See MDN Reference
`q`	`HTMLElementTagGlobalAttributes` & `object`	The q element represents some phrasing content quoted from another source. --- References See MDN Reference
`rb`	`HTMLElementTagGlobalAttributes`	The rb element marks the base text component of a ruby annotation. When it is the child of a ruby element, it doesn’t represent anything itself, but its parent ruby element uses it as part of determining what it represents. --- References See MDN Reference
`rp`	`HTMLElementTagGlobalAttributes`	The rp element is used to provide fallback text to be shown by user agents that don’t support ruby annotations. One widespread convention is to provide parentheses around the ruby text component of a ruby annotation. --- References See MDN Reference
`rt`	`HTMLElementTagGlobalAttributes`	The rt element marks the ruby text component of a ruby annotation. When it is the child of a ruby element or of an rtc element that is itself the child of a ruby element, it doesn’t represent anything itself, but its ancestor ruby element uses it as part of determining what it represents. --- References See MDN Reference
`ruby`	`HTMLElementTagGlobalAttributes`	The ruby element allows one or more spans of phrasing content to be marked with ruby annotations. Ruby annotations are short runs of text presented alongside base text, primarily used in East Asian typography as a guide for pronunciation or to include other annotations. In Japanese, this form of typography is also known as furigana. Ruby text can appear on either side, and sometimes both sides, of the base text, and it is possible to control its position using CSS. A more complete introduction to ruby can be found in the Use Cases & Exploratory Approaches for Ruby Markup document as well as in CSS Ruby Module Level 1. [RUBY-UC] [CSSRUBY] --- References See MDN Reference
`s`	`HTMLElementTagGlobalAttributes`	The s element represents contents that are no longer accurate or no longer relevant. --- References See MDN Reference
`samp`	`HTMLElementTagGlobalAttributes`	The samp element represents sample or quoted output from another program or computing system. --- References See MDN Reference
`script`	`HTMLElementTagGlobalAttributes` & `object`	The script element allows authors to include dynamic script and data blocks in their documents. The element does not represent content for the user. --- References See MDN Reference
`section`	`HTMLElementTagGlobalAttributes`	The section element represents a generic section of a document or application. A section, in this context, is a thematic grouping of content. Each section should be identified, typically by including a heading ( h1- h6 element) as a child of the section element. --- References See MDN Reference
`select`	`HTMLElementTagGlobalAttributes` & `object`	The select element represents a control for selecting amongst a set of options. --- References See MDN Reference
`slot`	`HTMLElementTagGlobalAttributes` & `object`	The slot element is a placeholder inside a web component that you can fill with your own markup, which lets you create separate DOM trees and present them together. --- References See MDN Reference
`small`	`HTMLElementTagGlobalAttributes`	The small element represents side comments such as small print. --- References See MDN Reference
`source`	`HTMLElementTagGlobalAttributes` & `object`	The source element allows authors to specify multiple alternative media resources for media elements. It does not represent anything on its own. --- References See MDN Reference
`span`	`HTMLElementTagGlobalAttributes`	The span element doesn’t mean anything on its own, but can be useful when used together with the global attributes, e.g. class, lang, or dir. It represents its children. --- References See MDN Reference
`strong`	`HTMLElementTagGlobalAttributes`	The strong element represents strong importance, seriousness, or urgency for its contents. --- References See MDN Reference
`style`	`HTMLElementTagGlobalAttributes` & `object`	The style element allows authors to embed style information in their documents. The style element is one of several inputs to the styling processing model. The element does not represent content for the user. --- References See MDN Reference
`sub`	`HTMLElementTagGlobalAttributes`	The sub element represents a subscript. --- References See MDN Reference
`summary`	`HTMLElementTagGlobalAttributes`	The summary element represents a summary, caption, or legend for the rest of the contents of the summary element’s parent details element, if any. --- References See MDN Reference
`sup`	`HTMLElementTagGlobalAttributes`	The sup element represents a superscript. --- References See MDN Reference
`table`	`HTMLElementTagGlobalAttributes` & `object`	The table element represents data with more than one dimension, in the form of a table. --- References See MDN Reference
`tbody`	`HTMLElementTagGlobalAttributes` & `object`	The tbody element represents a block of rows that consist of a body of data for the parent table element, if the tbody element has a parent and it is a table. --- References See MDN Reference
`td`	`HTMLElementTagGlobalAttributes` & `object`	The td element represents a data cell in a table. --- References See MDN Reference
`template`	`HTMLElementTagGlobalAttributes`	The template element is used to declare fragments of HTML that can be cloned and inserted in the document by script. --- References See MDN Reference
`textarea`	`HTMLElementTagGlobalAttributes` & `object`	The textarea element represents a multiline plain text edit control for the element’s raw value. The contents of the control represent the control’s default value. --- References See MDN Reference
`tfoot`	`HTMLElementTagGlobalAttributes` & `object`	The tfoot element represents the block of rows that consist of the column summaries (footers) for the parent table element, if the tfoot element has a parent and it is a table. --- References See MDN Reference
`th`	`HTMLElementTagGlobalAttributes` & `object`	The th element represents a header cell in a table. --- References See MDN Reference
`thead`	`HTMLElementTagGlobalAttributes` & `object`	The thead element represents the block of rows that consist of the column labels (headers) for the parent table element, if the thead element has a parent and it is a table. --- References See MDN Reference
`time`	`HTMLElementTagGlobalAttributes` & `object`	The time element represents its contents, along with a machine-readable form of those contents in the datetime attribute. The kind of content is limited to various kinds of dates, times, time-zone offsets, and durations, as described below. --- References See MDN Reference
`title`	`HTMLElementTagGlobalAttributes`	The title element represents the document’s title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user’s history or bookmarks, or in search results. The document’s title is often different from its first heading, since the first heading does not have to stand alone when taken out of context. --- References See MDN Reference
`tr`	`HTMLElementTagGlobalAttributes` & `object`	The tr element represents a row of cells in a table. --- References See MDN Reference
`track`	`HTMLElementTagGlobalAttributes` & `object`	The track element allows authors to specify explicit external timed text tracks for media elements. It does not represent anything on its own. --- References See MDN Reference
`u`	`HTMLElementTagGlobalAttributes`	The u element represents a span of text with an unarticulated, though explicitly rendered, non-textual annotation, such as labeling the text as being a proper name in Chinese text (a Chinese proper name mark), or labeling the text as being misspelt. --- References See MDN Reference
`ul`	`HTMLElementTagGlobalAttributes` & `object`	The ul element represents a list of items, where the order of the items is not important — that is, where changing the order would not materially change the meaning of the document. --- References See MDN Reference
`var`	`HTMLElementTagGlobalAttributes`	The var element represents a variable. This could be an actual variable in a mathematical expression or programming context, an identifier representing a constant, a symbol identifying a physical quantity, a function parameter, or just be a term used as a placeholder in prose. --- References See MDN Reference
`video`	`HTMLElementTagGlobalAttributes` & `object`	A video element is used for playing videos or movies, and audio files with captions. --- References See MDN Reference
`wbr`	`HTMLElementTagGlobalAttributes`	The wbr element represents a line break opportunity. --- References See MDN Reference

HTMLElementTagGlobalAttributes

1
type HTMLElementTagGlobalAttributes: object;

Global HTML attributes.

Remarks

If you need the type of all HTML attributes, this is it.

Example

1
const getAttribute = (attribute: keyof HTMLElementTagGlobalAttributes) => // …

See

ReadOnlyRecord

Type declaration

Member	Type	Description
`accesskey`	`string`	Provides a hint for generating a keyboard shortcut for the current element. This attribute consists of a space-separated list of characters. The browser should use the first one that exists on the computer keyboard layout. --- References See MDN Reference
`aria-activedescendant`	`string`	Identifies the currently active element when DOM focus is on a `composite` widget, `textbox`, `group`, or `application`. --- References See WAI-ARIA Reference
`aria-atomic`	`string`	Indicates whether assistive technologies will present all, or only parts of, the changed region based on the change notifications defined by the `aria-relevant` attribute. --- References See WAI-ARIA Reference
`aria-autocomplete`	`string`	Indicates whether inputting text could trigger display of one or more predictions of the user’s intended value for an input and specifies how predictions would be presented if they are made. --- References See WAI-ARIA Reference
`aria-busy`	`string`	Indicates an element is being modified and that assistive technologies MAY want to wait until the modifications are complete before exposing them to the user. --- References See WAI-ARIA Reference
`aria-checked`	`string`	Indicates the current “checked” state of checkboxes, radio buttons, and other widgets. See related `aria-pressed` and `aria-selected`. --- References See WAI-ARIA Reference
`aria-colcount`	`string`	Defines the total number of columns in a `table`, `grid`, or `treegrid`. See related `aria-colindex`. --- References See WAI-ARIA Reference
`aria-colindex`	`string`	Defines an element’s column index or position with respect to the total number of columns within a `table`, `grid`, or `treegrid`. See related `aria-colcount` and `aria-colspan`. --- References See WAI-ARIA Reference
`aria-colspan`	`string`	Defines the number of columns spanned by a cell or gridcell within a `table`, `grid`, or `treegrid`. See related `aria-colindex` and `aria-rowspan`. --- References See WAI-ARIA Reference
`aria-controls`	`string`	Identifies the element (or elements) whose contents or presence are controlled by the current element. See related `aria-owns`. --- References See WAI-ARIA Reference
`aria-current`	`string`	Indicates the element that represents the current item within a container or set of related elements. --- References See WAI-ARIA Reference
`aria-describedby`	`string`	Identifies the element (or elements) that describes the object. See related `aria-labelledby`. --- References See WAI-ARIA Reference
`aria-details`	`string`	Identifies the element that provides a detailed, extended description for the object. See related `aria-describedby`.
`aria-disabled`	`string`	Indicates that the element is perceivable but disabled, so it is not editable or otherwise operable. See related `aria-hidden` and `aria-readonly`. --- References See WAI-ARIA Reference
`aria-dropeffect`	`string`	[Deprecated in ARIA 1.1] Indicates what functions can be performed when a dragged object is released on the drop target. --- References See WAI-ARIA Reference
`aria-errormessage`	`string`	Identifies the element that provides an error message for the object. See related `aria-invalid` and `aria-describedby`. --- References See WAI-ARIA Reference
`aria-expanded`	`string`	Indicates whether the element, or another grouping element it controls, is currently expanded or collapsed. --- References See WAI-ARIA Reference
`aria-flowto`	`string`	Identifies the next element (or elements) in an alternate reading order of content which, at the user’s discretion, allows assistive technology to override the general default of reading in document source order. --- References See WAI-ARIA Reference
`aria-grabbed`	`string`	[Deprecated in ARIA 1.1] Indicates an element’s “grabbed” state in a drag-and-drop operation. --- References See WAI-ARIA Reference
`aria-haspopup`	`string`	Indicates the availability and type of interactive popup element, such as menu or dialog, that can be triggered by an element. --- References See WAI-ARIA Reference
`aria-hidden`	`string`	Indicates whether the element is exposed to an accessibility API. See related `aria-disabled`. --- References See WAI-ARIA Reference
`aria-invalid`	`string`	Indicates the entered value does not conform to the format expected by the application. See related `aria-errormessage`. --- References See WAI-ARIA Reference
`aria-keyshortcuts`	`string`	Indicates keyboard shortcuts that an author has implemented to activate or give focus to an element.
`aria-label`	`string`	Defines a string value that labels the current element. See related `aria-labelledby`. --- References See WAI-ARIA Reference
`aria-labelledby`	`string`	Identifies the element (or elements) that labels the current element. See related `aria-describedby`. --- References See WAI-ARIA Reference
`aria-level`	`string`	Defines the hierarchical level of an element within a structure. --- References See WAI-ARIA Reference
`aria-live`	`string`	Indicates that an element will be updated, and describes the types of updates the user agents, assistive technologies, and user can expect from the live region. --- References See WAI-ARIA Reference
`aria-modal`	`string`	Indicates whether an element is modal when displayed. --- References See WAI-ARIA Reference
`aria-multiline`	`string`	Indicates whether a text box accepts multiple lines of input or only a single line. --- References See WAI-ARIA Reference
`aria-multiselectable`	`string`	Indicates that the user may select more than one item from the current selectable descendants. --- References See WAI-ARIA Reference
`aria-orientation`	`string`	Indicates whether the element’s orientation is horizontal, vertical, or unknown/ambiguous. --- References See WAI-ARIA Reference
`aria-owns`	`string`	Identifies an element (or elements) in order to define a visual, functional, or contextual parent/child relationship between DOM elements where the DOM hierarchy cannot be used to represent the relationship. See related `aria-controls`. --- References See WAI-ARIA Reference
`aria-placeholder`	`string`	Defines a short hint (a word or short phrase) intended to aid the user with data entry when the control has no value. A hint could be a sample value or a brief description of the expected format. --- References See WAI-ARIA Reference
`aria-posinset`	`string`	Defines an element’s number or position in the current set of listitems or treeitems. Not required if all elements in the set are present in the DOM. See related `aria-setsize`. --- References See WAI-ARIA Reference
`aria-pressed`	`string`	Indicates the current “pressed” state of toggle buttons. See related `aria-checked` and `aria-selected`. --- References See WAI-ARIA Reference
`aria-readonly`	`string`	Indicates that the element is not editable, but is otherwise operable. See related `aria-disabled`. --- References See WAI-ARIA Reference
`aria-relevant`	`string`	Indicates what notifications the user agent will trigger when the accessibility tree within a live region is modified. See related `aria-atomic`. --- References See WAI-ARIA Reference
`aria-required`	`string`	Indicates that user input is required on the element before a form may be submitted. --- References See WAI-ARIA Reference
`aria-roledescription`	`string`	Defines a human-readable, author-localized description for the role of an element. --- References See WAI-ARIA Reference
`aria-rowcount`	`string`	Defines the total number of rows in a `table`, `grid`, or `treegrid`. See related `aria-rowindex`. --- References See WAI-ARIA Reference
`aria-rowindex`	`string`	Defines an element’s row index or position with respect to the total number of rows within a `table`, `grid`, or `treegrid`. See related `aria-rowcount` and `aria-rowspan`. --- References See WAI-ARIA Reference
`aria-rowspan`	`string`	Defines the number of rows spanned by a cell or gridcell within a `table`, `grid`, or `treegrid`. See related `aria-rowindex` and `aria-colspan`. --- References See WAI-ARIA Reference
`aria-selected`	`string`	Indicates the current “selected” state of various widgets. See related `aria-checked` and `aria-pressed`. --- References See WAI-ARIA Reference
`aria-setsize`	`string`	Defines the number of items in the current set of listitems or treeitems. Not required if all elements in the set are present in the DOM. See related `aria-posinset`. --- References See WAI-ARIA Reference
`aria-sort`	`string`	Indicates if items in a table or grid are sorted in ascending or descending order. --- References See WAI-ARIA Reference
`aria-valuemax`	`string`	Defines the maximum allowed value for a range widget. --- References See WAI-ARIA Reference
`aria-valuemin`	`string`	Defines the minimum allowed value for a range widget. --- References See WAI-ARIA Reference
`aria-valuenow`	`string`	Defines the current value for a range widget. See related `aria-valuetext`. --- References See WAI-ARIA Reference
`aria-valuetext`	`string`	Defines the human readable text alternative of `aria-valuenow` for a range widget. --- References See WAI-ARIA Reference
`autocapitalize`	`string`	Controls whether and how text input is automatically capitalized as it is entered/edited by the user. It can have the following values: _ `off` or `none`, no autocapitalization is applied (all letters default to lowercase) _ `on` or `sentences`, the first letter of each sentence defaults to a capital letter; all other letters default to lowercase _ `words`, the first letter of each word defaults to a capital letter; all other letters default to lowercase _ `characters`, all letters should default to uppercase --- References See MDN Reference
`class`	`string`	A space-separated list of the classes of the element. Classes allows CSS and JavaScript to select and access specific elements via the class selectors or functions like the method `Document.getElementsByClassName()`. --- References See MDN Reference
`contenteditable`	`string`	An enumerated attribute indicating if the element should be editable by the user. If so, the browser modifies its widget to allow editing. The attribute must take one of the following values: _ `true` or the empty string, which indicates that the element must be editable; _ `false`, which indicates that the element must not be editable. --- References See MDN Reference
`contextmenu`	`string`	The `[id](#attr-id)` of a `<menu>` to use as the contextual menu for this element. --- References See MDN Reference
`dir`	`string`	An enumerated attribute indicating the directionality of the element’s text. It can have the following values: _ `ltr`, which means left to right and is to be used for languages that are written from the left to the right (like English); _ `rtl`, which means right to left and is to be used for languages that are written from the right to the left (like Arabic); * `auto`, which lets the user agent decide. It uses a basic algorithm as it parses the characters inside the element until it finds a character with a strong directionality, then it applies that directionality to the whole element. --- References See MDN Reference
`draggable`	`string`	An enumerated attribute indicating whether the element can be dragged, using the Drag and Drop API. It can have the following values: _ `true`, which indicates that the element may be dragged _ `false`, which indicates that the element may not be dragged. --- References See MDN Reference
`dropzone`	`string`	An enumerated attribute indicating what types of content can be dropped on an element, using the Drag and Drop API. It can have the following values: _ `copy`, which indicates that dropping will create a copy of the element that was dragged _ `move`, which indicates that the element that was dragged will be moved to this new location. * `link`, will create a link to the dragged data.
`exportparts`	`string`	Used to transitively export shadow parts from a nested shadow tree into a containing light tree. --- References See MDN Reference
`hidden`	`string`	A Boolean attribute indicates that the element is not yet, or is no longer, relevant. For example, it can be used to hide elements of the page that can’t be used until the login process has been completed. The browser won’t render such elements. This attribute must not be used to hide content that could legitimately be shown. --- References See MDN Reference
`id`	`string`	Defines a unique identifier (ID) which must be unique in the whole document. Its purpose is to identify the element when linking (using a fragment identifier), scripting, or styling (with CSS). --- References See MDN Reference
`inputmode`	`string`	Provides a hint to browsers as to the type of virtual keyboard configuration to use when editing this element or its contents. Used primarily on `<input>` elements, but is usable on any element while in `[contenteditable](https://developer.mozilla.org/docs/Web/HTML/Global_attributes#attr-contenteditable)` mode. --- References See MDN Reference
`is`	`string`	Allows you to specify that a standard HTML element should behave like a registered custom built-in element (see Using custom elements for more details). --- References See MDN Reference
`itemid`	`string`	The unique, global identifier of an item. --- References See MDN Reference
`itemprop`	`string`	Used to add properties to an item. Every HTML element may have an `itemprop` attribute specified, where an `itemprop` consists of a name and value pair. --- References See MDN Reference
`itemref`	`string`	Properties that are not descendants of an element with the `itemscope` attribute can be associated with the item using an `itemref`. It provides a list of element ids (not `itemid`s) with additional properties elsewhere in the document. --- References See MDN Reference
`itemscope`	`string`	`itemscope` (usually) works along with `[itemtype](https://developer.mozilla.org/docs/Web/HTML/Global_attributes#attr-itemtype)` to specify that the HTML contained in a block is about a particular item. `itemscope` creates the Item and defines the scope of the `itemtype` associated with it. `itemtype` is a valid URL of a vocabulary (such as schema.org) that describes the item and its properties context. --- References See MDN Reference
`itemtype`	`string`	Specifies the URL of the vocabulary that will be used to define `itemprop`s (item properties) in the data structure. `[itemscope](https://developer.mozilla.org/docs/Web/HTML/Global_attributes#attr-itemscope)` is used to set the scope of where in the data structure the vocabulary set by `itemtype` will be active. --- References See MDN Reference
`lang`	`string`	Helps define the language of an element: the language that non-editable elements are in, or the language that editable elements should be written in by the user. The attribute contains one “language tag” (made of hyphen-separated “language subtags”) in the format defined in Tags for Identifying Languages (BCP47). xml:lang has priority over it. --- References See MDN Reference
`onabort`	`string`	The loading of a resource has been aborted.
`onblur`	`string`	An element has lost focus (does not bubble).
`oncanplay`	`string`	The user agent can play the media, but estimates that not enough data has been loaded to play the media up to its end without having to stop for further buffering of content.
`oncanplaythrough`	`string`	The user agent can play the media up to its end without having to stop for further buffering of content.
`onchange`	`string`	The change event is fired for , elements when a change to the element’s value is committed by the user.
`onclick`	`string`	A pointing device button has been pressed and released on an element.
`oncontextmenu`	`string`	The right button of the mouse is clicked (before the context menu is displayed).
`ondblclick`	`string`	A pointing device button is clicked twice on an element.
`ondrag`	`string`	An element or text selection is being dragged (every 350ms).
`ondragend`	`string`	A drag operation is being ended (by releasing a mouse button or hitting the escape key).
`ondragenter`	`string`	A dragged element or text selection enters a valid drop target.
`ondragleave`	`string`	A dragged element or text selection leaves a valid drop target.
`ondragover`	`string`	An element or text selection is being dragged over a valid drop target (every 350ms).
`ondragstart`	`string`	The user starts dragging an element or text selection.
`ondrop`	`string`	An element is dropped on a valid drop target.
`ondurationchange`	`string`	The duration attribute has been updated.
`onemptied`	`string`	The media has become empty; for example, this event is sent if the media has already been loaded (or partially loaded), and the load() method is called to reload it.
`onended`	`string`	Playback has stopped because the end of the media was reached.
`onerror`	`string`	A resource failed to load.
`onfocus`	`string`	An element has received focus (does not bubble).
`onformchange`	`string`	-
`onforminput`	`string`	-
`oninput`	`string`	The value of an element changes or the content of an element with the attribute contenteditable is modified.
`oninvalid`	`string`	A submittable element has been checked and doesn’t satisfy its constraints.
`onkeydown`	`string`	A key is pressed down.
`onkeypress`	`string`	A key is pressed down and that key normally produces a character value (use input instead).
`onkeyup`	`string`	A key is released.
`onload`	`string`	A resource and its dependent resources have finished loading.
`onloadeddata`	`string`	The first frame of the media has finished loading.
`onloadedmetadata`	`string`	The metadata has been loaded.
`onloadstart`	`string`	Progress has begun.
`onmousedown`	`string`	A pointing device button (usually a mouse) is pressed on an element.
`onmouseenter`	`string`	A pointing device is moved onto the element that has the listener attached.
`onmouseleave`	`string`	A pointing device is moved off the element that has the listener attached.
`onmousemove`	`string`	A pointing device is moved over an element.
`onmouseout`	`string`	A pointing device is moved off the element that has the listener attached or off one of its children.
`onmouseover`	`string`	A pointing device is moved onto the element that has the listener attached or onto one of its children.
`onmouseup`	`string`	A pointing device button is released over an element.
`onmousewheel`	`string`	-
`onpause`	`string`	Playback has been paused.
`onplay`	`string`	Playback has begun.
`onplaying`	`string`	Playback is ready to start after having been paused or delayed due to lack of data.
`onpointercancel`	`string`	The pointer is unlikely to produce any more events.
`onpointerdown`	`string`	The pointer enters the active buttons state.
`onpointerenter`	`string`	Pointing device is moved inside the hit-testing boundary.
`onpointerleave`	`string`	Pointing device is moved out of the hit-testing boundary.
`onpointerlockchange`	`string`	The pointer was locked or released.
`onpointerlockerror`	`string`	It was impossible to lock the pointer for technical reasons or because the permission was denied.
`onpointermove`	`string`	The pointer changed coordinates.
`onpointerout`	`string`	The pointing device moved out of hit-testing boundary or leaves detectable hover range.
`onpointerover`	`string`	The pointing device is moved into the hit-testing boundary.
`onpointerup`	`string`	The pointer leaves the active buttons state.
`onprogress`	`string`	In progress.
`onratechange`	`string`	The playback rate has changed.
`onreadystatechange`	`string`	The readyState attribute of a document has changed.
`onreset`	`string`	A form is reset.
`onresize`	`string`	The document view has been resized.
`onscroll`	`string`	The document view or an element has been scrolled.
`onseeked`	`string`	A seek operation completed.
`onseeking`	`string`	A seek operation began.
`onselect`	`string`	Some text is being selected.
`onshow`	`string`	A contextmenu event was fired on/bubbled to an element that has a contextmenu attribute
`onstalled`	`string`	The user agent is trying to fetch media data, but data is unexpectedly not forthcoming.
`onsubmit`	`string`	A form is submitted.
`onsuspend`	`string`	Media data loading has been suspended.
`ontimeupdate`	`string`	The time indicated by the currentTime attribute has been updated.
`onvolumechange`	`string`	The volume has changed.
`onwaiting`	`string`	Playback has stopped because of a temporary lack of data.
`part`	`string`	A space-separated list of the part names of the element. Part names allows CSS to select and style specific elements in a shadow tree via the `::part` pseudo-element. --- References See MDN Reference
`role`	`string`	-
`slot`	`string`	Assigns a slot in a shadow DOM shadow tree to an element: An element with a `slot` attribute is assigned to the slot created by the `<slot>` element whose `[name](https://developer.mozilla.org/docs/Web/HTML/Element/slot#attr-name)` attribute’s value matches that `slot` attribute’s value. --- References See MDN Reference
`spellcheck`	`string`	An enumerated attribute defines whether the element may be checked for spelling errors. It may have the following values: _ `true`, which indicates that the element should be, if possible, checked for spelling errors; _ `false`, which indicates that the element should not be checked for spelling errors. --- References See MDN Reference
`style`	`string`	Contains CSS styling declarations to be applied to the element. Note that it is recommended for styles to be defined in a separate file or files. This attribute and the `<style>` element have mainly the purpose of allowing for quick styling, for example for testing purposes. --- References See MDN Reference
`tabindex`	`string`	An integer attribute indicating if the element can take input focus (is focusable), if it should participate to sequential keyboard navigation, and if so, at what position. It can take several values: _ a negative value means that the element should be focusable, but should not be reachable via sequential keyboard navigation; _ `0` means that the element should be focusable and reachable via sequential keyboard navigation, but its relative order is defined by the platform convention; * a positive value means that the element should be focusable and reachable via sequential keyboard navigation; the order in which the elements are focused is the increasing value of the tabindex. If several elements share the same tabindex, their relative order follows their relative positions in the document. --- References See MDN Reference
`title`	`string`	Contains a text representing advisory information related to the element it belongs to. Such information can typically, but not necessarily, be presented to the user as a tooltip. --- References See MDN Reference
`translate`	`string`	An enumerated attribute that is used to specify whether an element’s attribute values and the values of its `Text` node children are to be translated when the page is localized, or whether to leave them unchanged. It can have the following values: _ empty string and `yes`, which indicates that the element will be translated. _ `no`, which indicates that the element will not be translated. --- References See MDN Reference

Iterables

IsomorphicIterable<Item>

1
type IsomorphicIterable<Item>: Readonly<AsyncIterable<Item> | Iterable<Item>>;

Value might be an AsyncIterable or just an Iterable (read-only).

Remarks

Union type useful when you want to accept both AsyncIterable and Iterable values, which is generally in asynchronous functions that can loop over @@asyncIterator or @@iterator values.

Example

1
const iterable: IsomorphicIterable<number> = [1, 2, 3];
2

3
for (const item of iterable) {
4
	console.log(item); // Works
5
}
6

7
for await (const item of iterable) {
8
	console.log(item); // Also works
9
}

See

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the iterable.

IsomorphicIterableItem<SourceIterable>

1
type IsomorphicIterableItem<SourceIterable>: SourceIterable extends IsomorphicIterable<infer Item> ? Item : never;

Type of the items of an IsomorphicIterable.

Remarks

Sometimes we have to get the item type out of an IsomorphicIterable. This type is meant to be used where inference is not an option.

Example

1
const iterable: IsomorphicIterable<number> = [1, 2, 3];
2
const item: IsomorphicIterableItem<typeof iterable> = 1;

See

IsomorphicIterable

Type parameters

Type parameter	Description
`SourceIterable` extends `IsomorphicIterable`	`IsomorphicIterable` type to get the item type from.`

IsomorphicIterableIterator<Item>

1
type IsomorphicIterableIterator<Item>: Readonly<AsyncIterableIterator<Item> | IterableIterator<Item>>;

Value might be an AsyncIterableIterator or just an IterableIterator (read-only).

Remarks

This is just an read-only alternative to AsyncIterableIterator or IterableIterator to avoid unwanted mutations.

Example

1
const iterable: IsomorphicIterableIterator<number> = [1, 2, 3];

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the `AsyncIterableIterator` or `IterableIterator`.

IsomorphicIterator<Item, Return, Next>

1
type IsomorphicIterator<Item, Return, Next>: Readonly<AsyncIterator<Item, Return, Next> | Iterator<Item, Return, Next>>;

Value might be an AsyncIterator or just an Iterator (read-only).

Remarks

This is just an read-only alternative to AsyncIterator or Iterator to avoid unwanted mutations.

Example

1
const iterator: IsomorphicIterator<number> = [1, 2, 3];

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the `AsyncIterator` or `Iterator`.
`Return`	`void`	Type of the return value in the `AsyncIterator` or `Iterator`.
`Next`	`void`	Type of the next value in the `AsyncIterator` or `Iterator`.

ReadOnlyIterable<Item>

1
type ReadOnlyIterable<Item>: Readonly<Iterable<Item>>;

Read-only Iterable.

Remarks

This is just an read-only alternative to Iterable to avoid unwanted mutations.

Example

1
const test1: ReadOnlyIterable<number> = [1, 2, 3]; // ok
2
const test2: ReadOnlyIterable<string> = [1, 2, 3]; // error

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the `Iterable`.

ReadOnlyIterableIterator<Item>

1
type ReadOnlyIterableIterator<Item>: Readonly<IterableIterator<Item>>;

Read-only IterableIterator.

Remarks

This is just an read-only alternative to IterableIterator to avoid unwanted mutations.

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the `IterableIterator`.

ReadOnlyIterator<Item, Return, Next>

1
type ReadOnlyIterator<Item, Return, Next>: Readonly<Iterator<Item, Return, Next>>;

Read-only Iterator.

Remarks

This is just an read-only alternative to Iterator to avoid unwanted mutations.

Type parameters

Type parameter	Value	Description
`Item`	`unknown`	Type of the items in the `Iterator`.
`Return`	`void`	Type of the return value in the `Iterator`.
`Next`	`void`	Type of the next value in the `Iterator`.

Number

Digit

1
type Digit: Enumerate<9>;

Valid digits (0 to 9).

Remarks

The idea with this type is to use it to construct others based on it, like for example Digit2 for 00 to 99.

Example

1
const numbers: Iterable<Digit> = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

See

Enumerate

Enumerate<To, Accumulator>

1
type Enumerate<To, Accumulator>: Accumulator["length"] extends To ? Accumulator[number] | To : Enumerate<To, [...Accumulator, Accumulator["length"]]>;

Union of numbers from 0 to To

Remarks

Recursively generates a type with an union of numbers from 0 to Length - 1. This has the same limit TypeScript has for recursive types.

Example

1
type From0To10 = Enumerate<10>;

Type parameters

Type parameter	Value	Description
`To` extends `number`	-	Last number of the union (starts at 0).
`Accumulator` extends `ReadonlyArray`<`number`>	[]	Accumulator for the recursion (for internal use).

MultiDigitNumberString

1
type MultiDigitNumberString: `${bigint}${bigint}`;

String with more than 1 number on it.

Remarks

This type is useful when a given string will need more than one number on it.

Example

1
const test1: MultiDigitNumberString = "01"; // ok
2
const test2: MultiDigitNumberString = "1"; // error

Numeric

1
type Numeric: bigint | number;

Types to represent numbers.

Remarks

The Numeric type is a union of number and bigint. It is useful for cases where a value could be either a regular JavaScript number or a BigInt.

Example

1
const numericNumber: Numeric = 42;
2
const numericBigInt: Numeric = 42n;

Radix

1
type Radix: Range<2, 36>;

Valid radix values (from 2 to 36).

Remarks

The Radix type is useful when working with number bases other than decimal. The radix defines the base of the number system being used. For example, a binary system has a radix of 2, a decimal system has a radix of 10, and a hexadecimal system has a radix of 16. The Radix type can be used to ensure that a given radix value is within the valid range of 2 to 36.

Example

1
const binary: Radix = 2;
2
const decimal: Radix = 10;
3
const hexadecimal: Radix = 16;

See

Range

Range<From, To>

1
type Range<From, To>: Exclude<Enumerate<To>, Enumerate<From>> | From;

Generates a range of numbers using Enumerate with given Length and omitting the first From numbers.

Remarks

This type is equivalent to an array of numbers where the first From elements are excluded and the length of the array is Length - From. The idea is to use it to generate a range of numbers from the given From, and of the given Length.

Example

1
type From5To10 = Range<5, 10>; // 5, 6, 7, 8, 9, 10

See

Enumerate

Type parameters

Type parameter
`From` extends `number`
`To` extends `number`

Object

Empty

1
type Empty: EmptyArray | EmptyRecord | EmptyString;

Empty array, object or string.

Remarks

Union type of EmptyArray, EmptyRecord and EmptyString, to signify values that are empty.

Example

1
const emptyString: Empty = "";
2
const emptyArray: Empty = [];
3
const emptyRecord: Empty = {};

See

EmptyArray
EmptyRecord
EmptyString

EmptyRecord

1
type EmptyRecord: ReadOnlyRecord<PropertyKey, never>;

Empty record (object).

Remarks

This is a type alias for an empty readonly record. Accessing properties gives undefined.

Example

1
const emptyRecord: EmptyRecord = {};

See

ReadOnlyRecord

Entry<Key, Value>

1
type Entry<Key, Value>: readonly [Key, Value];

Entry couple [key, value].

Remarks

It is a tuple of two elements, the first one being the key and the second one being the value of an object’s property.

Example

1
const entry: Entry<string, number> = ["🟢", 1];

Type parameters

Type parameter	Value	Description
`Key`	`PropertyKey`	Object’s properties type.
`Value`	`unknown`	Object’s values type.

EntryKey<Input>

1
type EntryKey<Input>: Input[0];

Key of an Entry.

Remarks

Util type to get the key of an Entry.

Example

1
const entry: Entry<string, number> = ["🟢", 1];
2
const entryKey: EntryKey<typeof entry> = entry[0];

See

Entry

Type parameters

Type parameter	Description
`Input` extends `Entry`	Entry type.

EntryOf<Type>

1
type EntryOf<Type>: Entry<KeyOf<Type>, ValueOf<Type>>;

Object or array Entry.

Remarks

Get the Entry type out of an object or array.

Example

1
const object = {
2
	"🟢": 1,
3
	"🟩": 2,
4
};
5
const entries: EntryOf<typeof object> = Object.entries(object)[0];

See

Entry
KeyOf
ValueOf

Type parameters

Type parameter	Description
`Type` extends `object`	Object or array type.

EntryValue<Input>

1
type EntryValue<Input>: Input[1];

Value of an Entry.

Remarks

Util type to get the value of an Entry.

Example

1
const entry: Entry<string, number> = ["🟢", 1];
2
const entryValue: EntryValue<typeof entry> = entry[1];

See

Entry

Type parameters

Type parameter	Description
`Input` extends `Entry`	Entry type.

KeyOf<Type>

1
type KeyOf<Type>: Type extends ArrayLike ? NeverFallback<Just<Exclude<Partial<Type>["length"], Type["length"]>>, number> : `${Exclude<keyof Type, symbol>}`;

Generic key for either object or array.

Remarks

Type to represent the type of the key in an array or object. It automatically omits symbol keys from objects, and uses number for arrays with dynamic length.

Example

1
const array = [1, 2, 3] as const;
2
const object = { "🟢": "🟩" } as const;
3

4
const arrayKey: KeyOf<typeof array> = 0;
5
const objectKey: KeyOf<typeof object> = "🟢";

Type parameters

Type parameter	Description
`Type` extends `object`	Object or array type.

MaybeEmpty<Input>

1
type MaybeEmpty<Input>: Either<Input, Input extends ReadOnlyArray ? EmptyArray : Input extends string ? EmptyString : Input extends ReadOnlyRecord ? EmptyRecord : undefined>;

Creates an union of the given type with a possible “empty” value.

Remarks

This type is useful to make clear that we expect a possible empty value.

Example

1
type Greet: MaybeEmpty<"Hello">; // "Hello" | ""
2
type Triple: MaybeEmpty<readonly [1, 2, 3]>; // readonly [1, 2, 3] | readonly []
3
type Foo: MaybeEmpty<{ readonly foo: "bar" }>; // { readonly foo: "bar" } | {}

See

Either
EmptyArray
EmptyRecord
EmptyString

Type parameters

Type parameter	Description
`Input`	Type to unite with it’s empty counterpart.

NotEmpty<Type>

1
type NotEmpty<Type>: Exclude<Type, Empty>;

Type for a non-empty ArrayLike, object or string.

Remarks

Example

1
const notEmptyString: NotEmpty<string> = "🟢";
2
const notEmptyArray: NotEmpty<ReadOnlyArray> = ["🟢", "🟩"];
3
const notEmptyRecord: NotEmpty<ReadOnlyRecord> = { "🟢": "🟩" };

See

Empty

Type parameters

Type parameter	Description
`Type` extends `ArrayLike` \| `object` \| `string`	The type to check.

ReadOnlyRecord<Key, Value>

1
type ReadOnlyRecord<Key, Value>: Readonly<Record<Key, Value>>;

Read-only record.

Remarks

There’s already a native Readonly and Record type, but this type has default type parameters to make it easier to use when the type of a record is unknown.

Example

1
const record: ReadOnlyRecord<string, Array<number>> = {
2
	"🟢": [1, 2, 3],
3
	"🟩": [4, 5, 6],
4
};
5
record["🟢"][0] = 7; // Error

Type parameters

Type parameter	Value	Description
`Key` extends `PropertyKey`	`PropertyKey`	Type of the keys in the record.
`Value`	`unknown`	Type of the values in the record.

ValueOf<Type>

1
type ValueOf<Type>: KeyOf<Type> extends keyof Type ? Type[KeyOf<Type>] : never;

Generic key for either object or array.

Remarks

This type is used to get the type of the values in a collection (items of an ArrayLike or properties of a Record).

Example

1
const object = {
2
	"🟢": 1,
3
	"🟩": 2,
4
};
5
const key: ValueOf<typeof object> = 1;

See

KeyOf

Type parameters

Type parameter	Description
`Type` extends `object`	Object or array type.

RegExp

RegularExpression

1
type RegularExpression: `/${string}/${RegularExpressionFlags}`;

String representing a regular expression.

Remarks

Safer than string and simpler than RegExp type to represent a regular expression. It RegularExpression to enforce flags to always have u and have a consistent order.

Example

1
const regex: RegularExpression = "/^[a-z]+$/u";

See

RegularExpressionFlags

1
type RegularExpressionFlags: `${MaybeEmpty<"g">}${MaybeEmpty<"i">}${MaybeEmpty<"m">}${MaybeEmpty<"s">}u`;

Possible combinations of regular expression flags (with mandatory u flag).

Remarks

Type union stricter than string type for RegExp flags. The unicode flag is mandatory to ensure unicode characters are always supported.

Example

1
const flags1: RegularExpressionFlags = "u";
2
const flags2: RegularExpressionFlags = "gu";
3
const flags3: RegularExpressionFlags = "iu";
4
const flags4: RegularExpressionFlags = "giu";

See

Regular Expressions

String

Empty

1
type Empty: EmptyArray | EmptyRecord | EmptyString;

Empty array, object or string.

Remarks

Union type of EmptyArray, EmptyRecord and EmptyString, to signify values that are empty.

Example

1
const emptyString: Empty = "";
2
const emptyArray: Empty = [];
3
const emptyRecord: Empty = {};

See

EmptyArray
EmptyRecord
EmptyString

EmptyString

1
type EmptyString: typeof EMPTY_STRING;

Empty string.

Remarks

This type is a string with no characters on it (length 0). EmptyString.

Example

1
const emptyString: EmptyString = "";

Head<Input>

1
type Head<Input>: HeadAndTail<Input>[0];

Initial value of an ArrayLike.

Remarks

Given a type argument (an ArrayLike), this returns the type of the item in index 0.

Example

1
const array = ["🟢", "🟩", "💚"];
2
const head: Head<typeof array> = "🟢";

See

ArrayLike
HeadAndTail

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	`ArrayLike` value (such as `Array` or `string`).

HeadAndTail<Input>

1
type HeadAndTail<Input>: Input extends readonly [infer HeadItem, infer TailItems] ? readonly [HeadItem, TailItems] : Input extends `${infer FirstCharacter}${infer RestOfString}` ? readonly [FirstCharacter, RestOfString] : Input extends EmptyArray | EmptyString ? readonly [undefined, Input] : readonly [Maybe<Input[number]>, Input];

Get a couple with the head and tail types of an ArrayLike.

Remarks

Given a type argument (an ArrayLike), this returns a couple with the type of the item in index 0 first, and the rest of the ArrayLike after.

Example

1
const array = ["🟢", "🟩", "💚"];
2
const headAndTail: HeadAndTail<typeof array> = ["🟢", ["🟩", "💚"]];

See

ArrayLike
EmptyArray
EmptyString
Head
Maybe
Tail

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	Input `ArrayLike`.

Initial<Input>

1
type Initial<Input>: InitialAndLast<Input>[0];

Initial values of an ArrayLike (omitting the last).

Remarks

Given a type argument (an ArrayLike), this returns the type of the items from the start of the ArrayLike until the before to last item.

Example

1
const array = ["🟢", "🟩", "💚"];
2
const initial: Initial<typeof array> = ["🟢", "🟩"];

See

ArrayLike
InitialAndLast

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	`ArrayLike` value (such as `Array` or `string`).

InitialAndLast<Input>

1
type InitialAndLast<Input>: Input extends readonly [...(infer InitialItems), infer LastItem] ? readonly [InitialItems, LastItem] : Input extends EmptyArray | EmptyString ? readonly [Input, undefined] : Input extends `${infer FirstCharacter}${infer RestOfString}` ? readonly [`${RestOfString extends EmptyString ? EmptyString : FirstCharacter}${Head<InitialAndLast<RestOfString>>}`, `${RestOfString extends EmptyString ? FirstCharacter : Last<RestOfString>}`] : readonly [Input, Maybe<Input[number]>];

Get a couple with the initial and last types of an ArrayLike.

Remarks

Given a ArrayLike, this returns a couple with the type of all items from the start until the item before last, and then the last.

Example

1
const array = ["🟢", "🟩", "💚"];
2
const initialAndLast: InitialAndLast<typeof array> = [["🟢", "🟩"], "💚"];

See

ArrayLike
EmptyArray
EmptyString
Head
Initial
Last
Maybe

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	Input `ArrayLike`.

Last<Input>

1
type Last<Input>: InitialAndLast<Input>[1];

Last value of an ArrayLike.

Remarks

Type of the last character of a string or the last element of an array.

Example

1
const array = ["🟢", "🟩", "💚"];
2
const last: Last<typeof array> = "💚";

See

ArrayLike
InitialAndLast

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	The input `ArrayLike`.

LocaleIdentifier

1
type LocaleIdentifier:
2
  | LocaleString<"ar",
3
  | "BH"
4
  | "DZ"
5
  | "JO"
6
  | "KW"
7
  | "OM"
8
  | "PS"
9
  | "QA"
10
  | `${"A" | "Y"}E`
11
  | `E${"G" | "H" | "R"}`
12
  | `I${"B" | "Y"}`
13
  | `I${"L" | "Q"}`
14
  | `M${"A" | "R"}`
15
  | `S${"A" | "D" | "O" | "S" | "Y"}`
16
  | `T${"D" | "N"}`>
17
  | LocaleString<"en",
18
  | "CA"
19
  | "HK"
20
  | "IE"
21
  | "JM"
22
  | "SG"
23
  | "TT"
24
  | "VI"
25
  | `A${"S" | "U"}`
26
  | `B${"E" | "W" | "Z"}`
27
  | `G${"B" | "U"}`
28
  | `I${"L" | "N"}`
29
  | `M${"H" | "P" | "T" | "U"}`
30
  | `N${"A" | "Z"}`
31
  | `P${"H" | "K"}`
32
  | `U${"M" | "S"}`
33
  | `Z${"A" | "W"}`>
34
  | LocaleString<"es",
35
  | "419"
36
  | "AR"
37
  | "BO"
38
  | "DO"
39
  | "HN"
40
  | "MX"
41
  | "NI"
42
  | "SV"
43
  | "VE"
44
  | `C${"L" | "O" | "R"}`
45
  | `E${"C" | "S"}`
46
  | `G${"Q" | "T"}`
47
  | `P${"A" | "E" | "R" | "Y"}`
48
  | `U${"S" | "Y"}`>
49
  | LocaleString<"fr",
50
  | "DJ"
51
  | "FR"
52
  | "KM"
53
  | "LU"
54
  | "NE"
55
  | "SN"
56
  | `B${"E" | "F" | "I" | "J" | "L"}`
57
  | `C${"A" | "D" | "F" | "G" | "H" | "I" | "M"}`
58
  | `G${"A" | "N" | "P" | "Q"}`
59
  | `M${"C" | "F" | "G" | "L" | "Q"}`
60
  | `R${"E" | "W"}`
61
  | `T${"D" | "G"}`>
62
  | LocaleString<"pa", LocaleString<"Arab", "PK"> | LocaleString<"Guru", "IN">>
63
  | LocaleString<"uz", LocaleString<"Arab", "AF"> | LocaleString<"Cyrl" | "Latn", "UZ">>
64
  | LocaleString<"zh", LocaleString<"Hans", "CN" | "SG"> | LocaleString<"Hant", "TW"> | LocaleString<`Han${"s" | "t"}`, "HK" | "MO">>
65
  | LocaleString<"af", `${"N" | "Z"}A`>
66
  | LocaleString<"ak", "GH">
67
  | LocaleString<"am", "ET">
68
  | LocaleString<"as", "IN">
69
  | LocaleString<"asa", "TZ">
70
  | LocaleString<"az", LocaleString<"Cyrl" | "Latn", "AZ">>
71
  | LocaleString<"be", "BY">
72
  | LocaleString<"bem", "ZM">
73
  | LocaleString<"bez", "TZ">
74
  | LocaleString<"bg", "BG">
75
  | LocaleString<"bm", "ML">
76
  | LocaleString<"bn", "BD" | "IN">
77
  | LocaleString<"bo", `${"C" | "I"}N`>
78
  | LocaleString<"bs", "BA">
79
  | LocaleString<"ca", "ES">
80
  | LocaleString<"cgg", "UG">
81
  | LocaleString<"chr", "US">
82
  | LocaleString<"cs", "CZ">
83
  | LocaleString<"cy", "GB">
84
  | LocaleString<"da", "DK">
85
  | LocaleString<"dav", "KE">
86
  | LocaleString<"de", "AT" | "CH" | `${"B" | "D"}E` | `L${"I" | "U"}`>
87
  | LocaleString<"ebu", "KE">
88
  | LocaleString<"ee", "GH" | "TG">
89
  | LocaleString<"el", "CY" | "GR">
90
  | LocaleString<"et", "EE">
91
  | LocaleString<"eu", "ES">
92
  | LocaleString<"fa", "AF" | "IR">
93
  | LocaleString<"ff", "SN">
94
  | LocaleString<"fi", "FI">
95
  | LocaleString<"fil", "PH">
96
  | LocaleString<"fo", "FO">
97
  | LocaleString<"ga", "IE">
98
  | LocaleString<"gl", "ES">
99
  | LocaleString<"gsw", "CH">
100
  | LocaleString<"gu", "IN">
101
  | LocaleString<"guz", "KE">
102
  | LocaleString<"gv", "GB">
103
  | LocaleString<"ha", LocaleString<"Latn", "GH" | `N${"E" | "G"}`>>
104
  | LocaleString<"haw", "US">
105
  | LocaleString<"he", "IL">
106
  | LocaleString<"hi", "IN">
107
  | LocaleString<"hr", "HR">
108
  | LocaleString<"hu", "HU">
109
  | LocaleString<"hy", "AM">
110
  | LocaleString<"id", "ID">
111
  | LocaleString<"ig", "NG">
112
  | LocaleString<"ii", "CN">
113
  | LocaleString<"is", "IS">
114
  | LocaleString<"it", "CH" | "IT">
115
  | LocaleString<"ja", "JP">
116
  | LocaleString<"jmc", "TZ">
117
  | LocaleString<"ka", "GE">
118
  | LocaleString<"kab", "DZ">
119
  | LocaleString<"kam", "KE">
120
  | LocaleString<"kde", "TZ">
121
  | LocaleString<"kea", "CV">
122
  | LocaleString<"khq", "ML">
123
  | LocaleString<"ki", "KE">
124
  | LocaleString<"kk", LocaleString<"Cyrl", "KZ">>
125
  | LocaleString<"kl", "GL">
126
  | LocaleString<"kln", "KE">
127
  | LocaleString<"km", "KH">
128
  | LocaleString<"kn", "IN">
129
  | LocaleString<"ko", "KR">
130
  | LocaleString<"kok", "IN">
131
  | LocaleString<"kw", "GB">
132
  | LocaleString<"lag", "TZ">
133
  | LocaleString<"lg", "UG">
134
  | LocaleString<"lt", "LT">
135
  | LocaleString<"luo", "KE">
136
  | LocaleString<"luy", "KE">
137
  | LocaleString<"lv", "LV">
138
  | LocaleString<"mas", "KE" | "TZ">
139
  | LocaleString<"mer", "KE">
140
  | LocaleString<"mfe", "MU">
141
  | LocaleString<"mg", "MG">
142
  | LocaleString<"mk", "MK">
143
  | LocaleString<"ml", "IN">
144
  | LocaleString<"mr", "IN">
145
  | LocaleString<"ms", "BN" | "MY">
146
  | LocaleString<"mt", "MT">
147
  | LocaleString<"my", "MM">
148
  | LocaleString<"naq", "NA">
149
  | LocaleString<"nb", "NO">
150
  | LocaleString<"nd", "ZW">
151
  | LocaleString<"ne", "IN" | "NP">
152
  | LocaleString<"nl", "BE" | "NL">
153
  | LocaleString<"nn", "NO">
154
  | LocaleString<"nyn", "UG">
155
  | LocaleString<"om", "ET" | "KE">
156
  | LocaleString<"or", "IN">
157
  | LocaleString<"pl", "PL">
158
  | LocaleString<"ps", "AF">
159
  | LocaleString<"pt", "BR" | "GW" | "MZ" | "PT">
160
  | LocaleString<"rm", "CH">
161
  | LocaleString<"ro", "MD" | "RO">
162
  | LocaleString<"rof", "TZ">
163
  | LocaleString<"ru", "MD" | "RU" | "UA">
164
  | LocaleString<"rw", "RW">
165
  | LocaleString<"rwk", "TZ">
166
  | LocaleString<"saq", "KE">
167
  | LocaleString<"seh", "MZ">
168
  | LocaleString<"ses", "ML">
169
  | LocaleString<"sg", "CF">
170
  | LocaleString<"shi", LocaleString<"Latn" | "Tfng", "MA">>
171
  | LocaleString<"si", "LK">
172
  | LocaleString<"sk", "SK">
173
  | LocaleString<"sl", "SI">
174
  | LocaleString<"sn", "ZW">
175
  | LocaleString<"so", "DJ" | "ET" | "KE" | "SO">
176
  | LocaleString<"sq", "AL">
177
  | LocaleString<"sr", LocaleString<"Cyrl" | "Latn", "BA" | "ME" | "RS">>
178
  | LocaleString<"sv", "FI" | "SE">
179
  | LocaleString<"sw", "KE" | "TZ">
180
  | LocaleString<"ta", "IN" | "LK">
181
  | LocaleString<"te", "IN">
182
  | LocaleString<"teo", "KE" | "UG">
183
  | LocaleString<"th", "TH">
184
  | LocaleString<"ti", `E${"R" | "T"}`>
185
  | LocaleString<"to", "TO">
186
  | LocaleString<"tr", "TR">
187
  | LocaleString<"tzm", LocaleString<"Latn", "MA">>
188
  | LocaleString<"uk", "UA">
189
  | LocaleString<"ur", "IN" | "PK">
190
  | LocaleString<"vi", "VN">
191
  | LocaleString<"vun", "TZ">
192
  | LocaleString<"xog", "UG">
193
  | LocaleString<"yo", "NG">
194
  | LocaleString<"zu", "ZA">
195
  | "eo"
196
  | "yue-Hant-HK";

Locale identifiers (language-country).

Remarks

When using i18n tools, this is a stricter union type than string to handle the locale identifiers.

Example

1
const locale: LocaleIdentifier = "en-US";

See

EmptyString

LocaleString<LanguageCode, CountryCodes, Separator>

1
type LocaleString<LanguageCode, CountryCodes, Separator>: `${LanguageCode}${MaybeEmpty<`${Separator}${CountryCodes}`>}`;

String for locales such as “en-US”.

Remarks

This type mainly exists to make LocaleIdentifier a little bit easier to the eyes.

Example

1
type English1: LocaleIdentifier<"en", "US" | "UK">; // "en" | "en-US" | "en-UK"
2
type English2: LocaleIdentifier<"en", "US" | "UK", "_">; // "en" | "en_US" | "en_UK"

See

LocaleIdentifier

Type parameters

Type parameter	Value	Description
`LanguageCode` extends `MultiCharacterString`	-	2 character language code.
`CountryCodes` extends `MultiCharacterString`	-	Union of country codes.
`Separator` extends `"_"` \| `"-"`	`"-"`	-

MaybeEmpty<Input>

1
type MaybeEmpty<Input>: Either<Input, Input extends ReadOnlyArray ? EmptyArray : Input extends string ? EmptyString : Input extends ReadOnlyRecord ? EmptyRecord : undefined>;

Creates an union of the given type with a possible “empty” value.

Remarks

This type is useful to make clear that we expect a possible empty value.

Example

1
type Greet: MaybeEmpty<"Hello">; // "Hello" | ""
2
type Triple: MaybeEmpty<readonly [1, 2, 3]>; // readonly [1, 2, 3] | readonly []
3
type Foo: MaybeEmpty<{ readonly foo: "bar" }>; // { readonly foo: "bar" } | {}

See

Either
EmptyArray
EmptyRecord
EmptyString

Type parameters

Type parameter	Description
`Input`	Type to unite with it’s empty counterpart.

MultiCharacterString

1
type MultiCharacterString: `${string}${string}`;

String with more than 1 character on it.

Deprecated

Not actually deprecated, this type doesn’t do anything yet.

Remarks

This type will be useful when a given string will need more than one character on it. Sadly this type doesn’t work because TypeScript considers "" a string, so "" + "" === string, same for "f" + "" which is not a multi character string.

Example

1
const test1: MultiCharacterString = "foo"; // ok
2
const test2: MultiCharacterString = "f"; // error

MultiDigitNumberString

1
type MultiDigitNumberString: `${bigint}${bigint}`;

String with more than 1 number on it.

Remarks

This type is useful when a given string will need more than one number on it.

Example

1
const test1: MultiDigitNumberString = "01"; // ok
2
const test2: MultiDigitNumberString = "1"; // error

NotEmpty<Type>

1
type NotEmpty<Type>: Exclude<Type, Empty>;

Type for a non-empty ArrayLike, object or string.

Remarks

Example

1
const notEmptyString: NotEmpty<string> = "🟢";
2
const notEmptyArray: NotEmpty<ReadOnlyArray> = ["🟢", "🟩"];
3
const notEmptyRecord: NotEmpty<ReadOnlyRecord> = { "🟢": "🟩" };

See

Empty

Type parameters

Type parameter	Description
`Type` extends `ArrayLike` \| `object` \| `string`	The type to check.

StringJoin<StrigifiableArray, Glue, Accumulator, LoopTracker>

1
type StringJoin<StrigifiableArray, Glue, Accumulator, LoopTracker>: LoopTracker["length"] extends StrigifiableArray["length"] ? Accumulator : StringJoin<StrigifiableArray, Glue, `${Accumulator}${Glue}${StrigifiableArray[LoopTracker["length"]]}`, [...LoopTracker, LoopTracker["length"]]>;

Joins all the items of the given strigifiable array using the given “glue”.

Remarks

Recursively generates a string type with the combination of the items of the given array. Ideal to use as the output type of a join function.

Example

1
type FooOrBar = StringJoin<readonly ["foo", "bar"], "|">; // "foo|bar"

Type parameters

Type parameter	Value	Description
`StrigifiableArray` extends `ReadOnlyArray`<`Strigifiable`>	-	Array to join.
`Glue` extends `string`	-	String to use to glue items together.
`Accumulator` extends `string`	`${StrigifiableArray[0]}`	-
`LoopTracker` extends `ReadOnlyArray`<`number`>	[`0`]	-

Tagger()<Output, Expressions>

1
type Tagger<Output, Expressions>: (templateStrings: TemplateStringsArray, ...expressions: Expressions) => Output;

Tag function for tagged templates.

Remarks

Type to represent a tag function for tagged templates, which takes a TemplateStringArray and any number of expressions, and returns a value of type Output (string by default).

Example

1
const intParser: Tagger<number> = strings => parseInt(strings.join(""), 10);
2
intParser`100`; // 100

See

ReadOnlyArray

Type parameters

Type parameter	Value	Description
`Output`	`string`	Type of the output value.
`Expressions` extends `ReadOnlyArray`	`ReadOnlyArray`	Type of the expressions.

Parameters

Parameter	Type
`templateStrings`	`TemplateStringsArray`
…`expressions`	`Expressions`

Returns

Output

Tail<Input>

1
type Tail<Input>: HeadAndTail<Input>[1];

Last values of an ArrayLike (omitting the first).

Remarks

Type of the last items of an ArrayLike, excluding the first item in said ArrayLike.

Example

1
const array = ["🟢", "🟩", "💚"];
2
const tail: Tail<typeof array> = ["🟩", "💚"];

See

ArrayLike
HeadAndTail

Type parameters

Type parameter	Description
`Input` extends `ArrayLike`	Type of the array to get the tail.