Types by Lou

🏷️ Collection of TypeScript types shared across Lou Codes projects.

Usage

📦 Node

Install @lou.codes/types as a dependency:

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

Import as type and use it:

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

🦕 Deno

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

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

Useful links

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

Array

ArrayLike

Ƭ ArrayLike<Item>: Object

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

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

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

Type parameters

Name	Type	Description
Item	unknown	Type of the items in the array-like object.

Index signature

▪ [index: number]: Item

Item of the ArrayLike.

Type declaration

Name	Type	Description
length	number	Amount of items in the ArrayLike.

View source

---

Empty

Ƭ Empty: EmptyArray | EmptyRecord | EmptyString

Empty array, object or string.

Remarks

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

Example

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

See

• EmptyArray
• EmptyRecord
• EmptyString

View source

---

EmptyArray

Ƭ EmptyArray: readonly []

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

const emptyArray: EmptyArray = [];

View source

---

Entry

Ƭ Entry<Key, Value>: readonly [key: Key, value: 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

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

Type parameters

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

View source

---

EntryKey

Ƭ EntryKey<Input>: First<Input>

Key of an Entry.

Remarks

Util type to get the key of an Entry.

Example

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

See

• Entry
• First

Type parameters

Name	Type	Description
Input	extends Entry	Entry type.

View source

---

EntryOf

Ƭ EntryOf<Input>: Entry<KeyOf<Input>, ValueOf<Input>>

Object or array Entry.

Remarks

Get the Entry type out of an object or array.

Example

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

See

• Entry
• KeyOf
• ReadOnlyCollection
• ValueOf

Type parameters

Name	Type	Description
Input	extends ReadOnlyCollection	Array or record type.

View source

---

EntryValue

Ƭ EntryValue<Input>: Second<Input>

Value of an Entry.

Remarks

Util type to get the value of an Entry.

Example

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

See

• Entry
• Second

Type parameters

Name	Type	Description
Input	extends Entry	Entry type.

View source

---

First

Ƭ First<Input>: Input[0]

First value of an ArrayLike.

Remarks

Type of the first item of an ArrayLike, mainly here to avoid magic numbers.

Example

const array = ["🟢", "🟩", "💚"];
const first: First<typeof array> = "🟢";

See

• ArrayLike
• InitialAndLast

Type parameters

Name	Type	Description
Input	extends ArrayLike	The input ArrayLike.

View source

---

Head

Ƭ Head<Input>: First<HeadAndTail<Input>>

Initial value of an ArrayLike.

Remarks

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

Example

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

See

• ArrayLike
• First
• HeadAndTail

Type parameters

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

View source

---

HeadAndTail

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

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

See

• ArrayLike
• EmptyArray
• EmptyString
• Head
• Maybe
• Tail

Type parameters

Name	Type	Description
Input	extends ArrayLike	Input ArrayLike.

View source

---

Initial

Ƭ Initial<Input>: First<InitialAndLast<Input>>

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

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

See

• ArrayLike
• First
• InitialAndLast

Type parameters

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

View source

---

InitialAndLast

Ƭ InitialAndLast<Input>: Input extends readonly […(infer InitialItems), infer LastItem] ? readonly [initial: InitialItems, last: LastItem] : Input extends EmptyArray | EmptyString ? readonly [initial: Input, last: undefined] : Input extends `${infer FirstCharacter}${infer RestOfString}` ? readonly [initial: `${RestOfString extends EmptyString ? EmptyString : FirstCharacter}${Head<InitialAndLast<RestOfString>>}`, last: `${RestOfString extends EmptyString ? FirstCharacter : Last<RestOfString>}`] : readonly [initial: Input, last: 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

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

See

• ArrayLike
• EmptyArray
• EmptyString
• Head
• Initial
• Last
• Maybe

Type parameters

Name	Type	Description
Input	extends ArrayLike	Input ArrayLike.

View source

---

KeyOf

Ƭ KeyOf<Input>: Input extends ArrayLike ? NeverFallback<Defined<Exclude<Partial<Input>["length"], Input["length"]>>, number> : `${Exclude<keyof Input, symbol>}`

Generic key for either object or array.

Remarks

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

Example

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

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

See

ReadOnlyCollection

Type parameters

Name	Type	Description
Input	extends ReadOnlyCollection	The input ReadOnlyCollection.

View source

---

Last

Ƭ Last<Input>: Second<InitialAndLast<Input>>

Last value of an ArrayLike.

Remarks

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

Example

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

See

• ArrayLike
• InitialAndLast
• Second

Type parameters

Name	Type	Description
Input	extends ArrayLike	The input ArrayLike.

View source

---

NotEmpty

Ƭ 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

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

See

Empty

Type parameters

Name	Type	Description
Type	extends ArrayLike | object | string	The type to check.

View source

---

ReadOnly

Ƭ ReadOnly<Input>: Input extends Readonly<ReadonlyMap<infer Key, infer Value>> ? Readonly<ReadonlyMap<ReadOnly<Key>, ReadOnly<Value>>> : Input extends Readonly<ReadonlySet<infer Item>> ? Readonly<ReadonlySet<ReadOnly<Item>>> : Input extends readonly [] ? readonly [] : Input extends readonly [infer Head, …(infer Tail)] ? readonly [ReadOnly<Head>, …ReadOnly<Tail>] : Input extends ReadonlyArray<infer Item> ? ReadonlyArray<ReadOnly<Item>> : Input extends Function ? Input : Input extends object ? { readonly [Property in keyof Input]: ReadOnly<Input[Property]> } : Input

Read-only deep any Input.

Remarks

This type makes any Input read-only recursively, including nested objects and arrays, Sets, Maps, and functions.

Example

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

Type parameters

Name	Description
Input	The type to make read-only.

View source

---

ReadOnlyArray

Ƭ ReadOnlyArray<Item>: ReadOnly<Item[]>

Read-only array.

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, plus it recursively makes all the items in the array read-only.

Example

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

See

ReadOnly

Type parameters

Name	Type	Description
Item	unknown	Type of the items in the array.

View source

---

ReadOnlyCollection

Ƭ ReadOnlyCollection<Item>: ArrayLike<Item> | ReadOnlyRecord<PropertyKey, Item>

Read-only collection (ArrayLike or ReadOnlyRecord).

Remarks

Read-only type union of ArrayLike or ReadOnlyRecord.

Example

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

See

• ArrayLike
• ReadOnlyRecord

Type parameters

Name	Type	Description
Item	unknown	Type of the items in the collection.

View source

---

Reducer

Ƭ 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

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

See

Unary

Type parameters

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

View source

---

Second

Ƭ Second<Input>: Input[1]

Second value of an ArrayLike.

Remarks

Type of the Second item of an ArrayLike, manly here to avoid magic numbers.

Example

const array = ["🟢", "🟩", "💚"];
const second: Second<typeof array> = "🟩";

See

• ArrayLike
• InitialAndLast

Type parameters

Name	Type	Description
Input	extends ArrayLike	The input ArrayLike.

View source

---

Sorter

Ƭ Sorter<Item>: Unary<Item, Unary<Item, number>>

Curried sorter Unary function.

Remarks

Type to represent a function that takes two items and returns a number to determine their order. If the result is negative, the first item is sorted before the second item. If the result is positive, the first item is sorted after the second item. If the result is zero, the order of the items is unchanged.

Example

const sorter: Sorter<number> = value1 => value2 => value1 - value2;

See

• Unary
• Array.prototype.sort
• Array.prototype.toSorted

Type parameters

Name	Description
Item	Type of the items to sort.

View source

---

Tail

Ƭ Tail<Input>: Second<HeadAndTail<Input>>

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

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

See

• ArrayLike
• HeadAndTail
• Second

Type parameters

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

View source

---

ValueOf

Ƭ ValueOf<Input>: Input[KeyOf<Input> & keyof Input]

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

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

See

ReadOnlyCollection

Type parameters

Name	Type	Description
Input	extends ReadOnlyCollection	Type of the collection.

View source

Common

Awaitable

Ƭ Awaitable<Type>: Promise<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

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

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

See

Promise

Type parameters

Name	Type	Description
Type	unknown	The type to await.

View source

---

Defined

Ƭ Defined<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

const maybeUndefined: string | undefined = "🟢";
const definitelyDefined: Defined<typeof maybeUndefined> = "🟢";

See

Maybe

Type parameters

Name
Input

View source

---

Falsy

Ƭ Falsy: EmptyString | HTMLAllCollection | Nullish | 0 | 0n | 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

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

See

• Nullish
• Falsy

View source

---

JSONValue

Ƭ JSONValue: Exclude<Primitive, bigint | symbol | undefined> | ReadonlyArray<JSONValue> | { [property: string]: JSONValue; }

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

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

See

JSON

View source

---

LocaleIdentifier

Ƭ LocaleIdentifier: "eo" | "yue-Hant-HK" | `af${EmptyString | “-NA” | “-ZA”}` | `ak${EmptyString | “-GH”}` | `am${EmptyString | “-ET”}` | `ar${EmptyString | “-AE” | “-BH” | “-DZ” | “-EG” | “-EH” | “-ER” | “-IL” | “-IQ” | “-JO” | “-KW” | “-LB” | “-LY” | “-MA” | “-MR” | “-OM” | “-PS” | “-QA” | “-SA” | “-SD” | “-SO” | “-SS” | “-SY” | “-TD” | “-TN” | “-YE”}` | `as${EmptyString | “-IN”}` | `asa${EmptyString | “-TZ”}` | `az${EmptyString | `-Cyrl${EmptyString | “-AZ”}` | `-Latn${EmptyString | “-AZ”}`}` | `be${EmptyString | “-BY”}` | `bem${EmptyString | “-ZM”}` | `bez${EmptyString | “-TZ”}` | `bg${EmptyString | “-BG”}` | `bm${EmptyString | “-ML”}` | `bn${EmptyString | “-BD” | “-IN”}` | `bo${EmptyString | “-CN” | “-IN”}` | `bs${EmptyString | “-BA”}` | `ca${EmptyString | “-ES”}` | `cgg${EmptyString | “-UG”}` | `chr${EmptyString | “-US”}` | `cs${EmptyString | “-CZ”}` | `cy${EmptyString | “-GB”}` | `da${EmptyString | “-DK”}` | `dav${EmptyString | “-KE”}` | `de${EmptyString | “-AT” | “-BE” | “-CH” | “-DE” | “-LI” | “-LU”}` | `ebu${EmptyString | “-KE”}` | `ee${EmptyString | “-GH” | “-TG”}` | `el${EmptyString | “-CY” | “-GR”}` | `en${EmptyString | “-AS” | “-AU” | “-BE” | “-BW” | “-BZ” | “-CA” | “-GB” | “-GU” | “-HK” | “-IE” | “-IL” | “-IN” | “-JM” | “-MH” | “-MP” | “-MT” | “-MU” | “-NA” | “-NZ” | “-PH” | “-PK” | “-SG” | “-TT” | “-UM” | “-US” | “-VI” | “-ZA” | “-ZW”}` | `es${EmptyString | “-419” | “-AR” | “-BO” | “-CL” | “-CO” | “-CR” | “-DO” | “-EC” | “-ES” | “-GQ” | “-GT” | “-HN” | “-MX” | “-NI” | “-PA” | “-PE” | “-PR” | “-PY” | “-SV” | “-US” | “-UY” | “-VE”}` | `et${EmptyString | “-EE”}` | `eu${EmptyString | “-ES”}` | `fa${EmptyString | “-AF” | “-IR”}` | `ff${EmptyString | “-SN”}` | `fi${EmptyString | “-FI”}` | `fil${EmptyString | “-PH”}` | `fo${EmptyString | “-FO”}` | `fr${EmptyString | “-BE” | “-BF” | “-BI” | “-BJ” | “-BL” | “-CA” | “-CD” | “-CF” | “-CG” | “-CH” | “-CI” | “-CM” | “-DJ” | “-FR” | “-GA” | “-GN” | “-GP” | “-GQ” | “-KM” | “-LU” | “-MC” | “-MF” | “-MG” | “-ML” | “-MQ” | “-NE” | “-RE” | “-RW” | “-SN” | “-TD” | “-TG”}` | `ga${EmptyString | “-IE”}` | `gl${EmptyString | “-ES”}` | `gsw${EmptyString | “-CH”}` | `gu${EmptyString | “-IN”}` | `guz${EmptyString | “-KE”}` | `gv${EmptyString | “-GB”}` | `ha${EmptyString | `-Latn${EmptyString | “-GH” | “-NE” | “-NG”}`}` | `haw${EmptyString | “-US”}` | `he${EmptyString | “-IL”}` | `hi${EmptyString | “-IN”}` | `hr${EmptyString | “-HR”}` | `hu${EmptyString | “-HU”}` | `hy${EmptyString | “-AM”}` | `id${EmptyString | “-ID”}` | `ig${EmptyString | “-NG”}` | `ii${EmptyString | “-CN”}` | `is${EmptyString | “-IS”}` | `it${EmptyString | “-CH” | “-IT”}` | `ja${EmptyString | “-JP”}` | `jmc${EmptyString | “-TZ”}` | `ka${EmptyString | “-GE”}` | `kab${EmptyString | “-DZ”}` | `kam${EmptyString | “-KE”}` | `kde${EmptyString | “-TZ”}` | `kea${EmptyString | “-CV”}` | `khq${EmptyString | “-ML”}` | `ki${EmptyString | “-KE”}` | `kk${EmptyString | `-Cyrl${EmptyString | “-KZ”}`}` | `kl${EmptyString | “-GL”}` | `kln${EmptyString | “-KE”}` | `km${EmptyString | “-KH”}` | `kn${EmptyString | “-IN”}` | `ko${EmptyString | “-KR”}` | `kok${EmptyString | “-IN”}` | `kw${EmptyString | “-GB”}` | `lag${EmptyString | “-TZ”}` | `lg${EmptyString | “-UG”}` | `lt${EmptyString | “-LT”}` | `luo${EmptyString | “-KE”}` | `luy${EmptyString | “-KE”}` | `lv${EmptyString | “-LV”}` | `mas${EmptyString | “-KE” | “-TZ”}` | `mer${EmptyString | “-KE”}` | `mfe${EmptyString | “-MU”}` | `mg${EmptyString | “-MG”}` | `mk${EmptyString | “-MK”}` | `ml${EmptyString | “-IN”}` | `mr${EmptyString | “-IN”}` | `ms${EmptyString | “-BN” | “-MY”}` | `mt${EmptyString | “-MT”}` | `my${EmptyString | “-MM”}` | `naq${EmptyString | “-NA”}` | `nb${EmptyString | “-NO”}` | `nd${EmptyString | “-ZW”}` | `ne${EmptyString | “-IN” | “-NP”}` | `nl${EmptyString | “-BE” | “-NL”}` | `nn${EmptyString | “-NO”}` | `nyn${EmptyString | “-UG”}` | `om${EmptyString | “-ET” | “-KE”}` | `or${EmptyString | “-IN”}` | `pa${EmptyString | `-Arab${EmptyString | “-PK”}` | `-Guru${EmptyString | “-IN”}`}` | `pl${EmptyString | “-PL”}` | `ps${EmptyString | “-AF”}` | `pt${EmptyString | “-BR” | “-GW” | “-MZ” | “-PT”}` | `rm${EmptyString | “-CH”}` | `ro${EmptyString | “-MD” | “-RO”}` | `rof${EmptyString | “-TZ”}` | `ru${EmptyString | “-MD” | “-RU” | “-UA”}` | `rw${EmptyString | “-RW”}` | `rwk${EmptyString | “-TZ”}` | `saq${EmptyString | “-KE”}` | `seh${EmptyString | “-MZ”}` | `ses${EmptyString | “-ML”}` | `sg${EmptyString | “-CF”}` | `shi${EmptyString | `-Latn${EmptyString | “-MA”}` | `-Tfng${EmptyString | “-MA”}`}` | `si${EmptyString | “-LK”}` | `sk${EmptyString | “-SK”}` | `sl${EmptyString | “-SI”}` | `sn${EmptyString | “-ZW”}` | `so${EmptyString | “-DJ” | “-ET” | “-KE” | “-SO”}` | `sq${EmptyString | “-AL”}` | `sr${EmptyString | `-Cyrl${EmptyString | “-BA” | “-ME” | “-RS”}` | `-Latn${EmptyString | “-BA” | “-ME” | “-RS”}`}` | `sv${EmptyString | “-FI” | “-SE”}` | `sw${EmptyString | “-KE” | “-TZ”}` | `ta${EmptyString | “-IN” | “-LK”}` | `te${EmptyString | “-IN”}` | `teo${EmptyString | “-KE” | “-UG”}` | `th${EmptyString | “-TH”}` | `ti${EmptyString | “-ER” | “-ET”}` | `to${EmptyString | “-TO”}` | `tr${EmptyString | “-TR”}` | `tzm${EmptyString | `-Latn${EmptyString | “-MA”}`}` | `uk${EmptyString | “-UA”}` | `ur${EmptyString | “-IN” | “-PK”}` | `uz${EmptyString | `-Arab${EmptyString | “-AF”}` | `-Cyrl${EmptyString | “-UZ”}` | `-Latn${EmptyString | “-UZ”}`}` | `vi${EmptyString | “-VN”}` | `vun${EmptyString | “-TZ”}` | `xog${EmptyString | “-UG”}` | `yo${EmptyString | “-NG”}` | `zh${EmptyString | `-Hans${EmptyString | “-CN” | “-HK” | “-MO” | “-SG”}` | `-Hant${EmptyString | “-HK” | “-MO” | “-TW”}`}` | `zu${EmptyString | “-ZA”}`

Locale identifiers (language-country).

Remarks

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

Example

const locale: LocaleIdentifier = "en-US";

See

EmptyString

View source

---

Maybe

Ƭ Maybe<Value>: Value | 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

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

Type parameters

Name	Description
Value	The type of the value to make optional.

View source

---

NeverFallback

Ƭ 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

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

Type parameters

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

View source

---

Nullish

Ƭ 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

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

See

• Maybe
• Nullish

View source

---

Primitive

Ƭ Primitive: Nullish | Numeric | boolean | string | 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

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

See

• Nullish
• Numeric
• Primitive

View source

---

ReplaceType

Ƭ ReplaceType<Type, Keys, NewType>: ReadOnly<Omit<Type, Keys>> & ReadOnlyRecord<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

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

See

• ReadOnly
• ReadOnlyRecord

Type parameters

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

View source

---

Single

Ƭ Single<Type>: readonly [single: 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

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

Type parameters

Name	Description
Type	Type of the single element.

View source

---

Strigifiable

Ƭ 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

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

See

Primitive

View source

---

Truthy

Ƭ 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

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

See

Falsy

Type parameters

Name	Type	Description
Type	unknown	Type to exclude Falsy values from.

View source

---

TypeOfDictionary

Ƭ TypeOfDictionary: Object

typeof dictionary.

Remarks

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

Example

TypeOfMap["string"]; // `string`
TypeOfMap["boolean"]; // `boolean`
TypeOfMap["function"]; // `GenericFunction`

See

• typeof null bug
• typeof typeof rejected proposal

Type declaration

Name	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

View source

---

TypeOfValue

Ƭ 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

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

See

• TypeOfDictionary
• typeof null bug
• typeof typeof rejected proposal

View source

Date

DayOfMonth

Ƭ 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

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

See

• Enumerate
• Date

View source

---

DayOfWeek

Ƭ 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

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

See

• Enumerate
• Date

View source

---

Hours

Ƭ 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

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

See

• Enumerate
• Date

View source

---

ISODate

Ƭ ISODate: `${ISOYear}-${ISOMonth}-${ISODayOfMonth}T${bigint}${bigint}:${bigint}${bigint}:${bigint}${bigint}.${bigint}${bigint}${bigint}Z`

String representing an ISO date.

Remarks

This type is a string representing an ISO 8601 format of a date (returned by Date.prototype.toISOString).

Example

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

See

• ISO 8601
• Date
• Date.prototype.toISOString

View source

---

ISODayOfMonth

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

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

See

• Digit
• Enumerate
• Date

View source

---

ISOHours

Ƭ 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

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

See

• Enumerate
• Date

View source

---

ISOMilliseconds

Ƭ 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

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

See

• Date
• Digit

View source

---

ISOMinutes

Ƭ 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

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

See

• Date
• Digit
• Enumerate

View source

---

ISOMonth

Ƭ 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

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

See

• Date
• Digit
• Enumerate

View source

---

ISOSeconds

Ƭ 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

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

See

• Date
• Digit
• Enumerate

View source

---

ISOYear

Ƭ ISOYear: `${EmptyString | ”-”}${number}`

ISO year values in string format (from "-271821" to "275760").

Remarks

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

Example

const years: Iterable<ISOYear> = ["2020", "-1000", "1989"];

See

Date

View source

---

Milliseconds

Ƭ 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

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

See

• Date
• Enumerate

View source

---

Minutes

Ƭ 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

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

See

• Date
• Enumerate

View source

---

Month

Ƭ 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

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

See

• Date
• Enumerate

View source

---

Seconds

Ƭ 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

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

See

• Date
• Enumerate

View source

Function

Class

Ƭ Class<Arguments, Instance>: (…classArguments: Arguments) => Instance

Type parameters

Name	Type	Description
Arguments	extends ReadOnlyArray = ReadOnlyArray	Arguments of the class constructor.
Instance	unknown	Instance of the class.

Type declaration

• (...classArguments): Instance

A generic type for classes.

Parameters

Name	Type	Description
...classArguments	Arguments	Arguments of the class constructor.

Returns

Instance

Instance of the class.

Remarks

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

Example

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

See

ReadOnlyArray

View source

---

Comparison

Ƭ Comparison<Right, Left, Predicated>: Unary<Right, Single<Predicated> extends Single<never> ? Filter<Left> : Predicate<Left, Predicated>>

Comparison curried function.

Remarks

Curried function that takes a Right and a Left value and returns a boolean representing a comparison between them.

Example

const biggerThan: Comparison<number> = right => left => right > left;

See

• Predicate
• Unary

Param

Right-hand side of the comparison.

Type parameters

Name	Type	Description
Right	unknown	Right-hand side of the comparison.
Left	extends Right = Right	Left-hand side of the comparison.
Predicated	extends Left = never	Type of the value if Predicate returns true.

View source

---

Filter

Ƭ 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

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

See

Param

The input value to check.

Type parameters

Name	Description
Input	The type of the input value.

View source

---

Function

Ƭ Function<Arguments, Output>: (…input: Arguments) => Output

Type parameters

Name	Type	Description
Arguments	extends ReadOnlyArray = ReadOnlyArray	Arguments of the function.
Output	unknown	Output of the function.

Type declaration

▸ (...input): Output

Generic function type (safer than using any).

Parameters

Name	Type
...input	Arguments

Returns

Output

Output of the function.

Remarks

This type is a generic function type, for callbacks and other places where any type of function can be received.

Example

const example = (callback: Function) => callback("test");

See

ReadOnlyArray

View source

---

Predicate

Ƭ Predicate<Input, Predicated>: (input: Input) => input is Predicated

Type parameters

Name	Type	Description
Input	Input	The type of the input value.
Predicated	extends Input = Input	The subset of Input for which the predicate holds.

Type declaration

▸ (input): input is Predicated

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

Parameters

Name	Type	Description
input	Input	The input value to check.

Returns

input is Predicated

true if the predicate holds for the input value, and false otherwise.

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

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

See

View source

---

ReadOnlyArguments

Ƭ 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

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

See

• Function
• ReadOnly
• ReadOnlyArray

Type parameters

Name	Type	Description
Input	extends Function<ReadOnlyArray<never>>	Function to extract parameters from.

View source

---

Reducer

Ƭ 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

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

See

Unary

Type parameters

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

View source

---

Sorter

Ƭ Sorter<Item>: Unary<Item, Unary<Item, number>>

Curried sorter Unary function.

Remarks

Type to represent a function that takes two items and returns a number to determine their order. If the result is negative, the first item is sorted before the second item. If the result is positive, the first item is sorted after the second item. If the result is zero, the order of the items is unchanged.

Example

const sorter: Sorter<number> = value1 => value2 => value1 - value2;

See

• Unary
• Array.prototype.sort
• Array.prototype.toSorted

Type parameters

Name	Description
Item	Type of the items to sort.

View source

---

Tagger

Ƭ Tagger<Output, Expressions>: Function<readonly [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

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

See

• Function
• ReadOnly
• ReadOnlyArray

Type parameters

Name	Type	Description
Output	string	Type of the output value.
Expressions	extends ReadOnlyArray = ReadOnlyArray	Type of the expressions.

View source

---

Unary

Ƭ Unary<Input, Output>: Function<Single<Input>, Output>

Unary function.

Remarks

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

Example

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

See

• Function
• Single

Type parameters

Name	Description
Input	Type of the input value.
Output	Type of the output value.

View source

---

UnaryInput

Ƭ 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

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

See

Unary

Type parameters

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

View source

---

UnaryOutput

Ƭ 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

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

See

Unary

Type parameters

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

View source

HTML

HTMLElementTagAttributeMap

Ƭ HTMLElementTagAttributeMap: ReadOnlyRecord<`${string}-${string}`, HTMLElementTagGlobalAttributes> & { a: HTMLElementTagGlobalAttributes & { download?: string ; href?: string ; hreflang?: string ; ping?: string ; referrerpolicy?: string ; rel?: string ; target?: string ; type?: string } ; abbr: HTMLElementTagGlobalAttributes ; address: HTMLElementTagGlobalAttributes ; area: HTMLElementTagGlobalAttributes & { accesskey?: string ; alt?: string ; coords?: string ; download?: string ; href?: string ; hreflang?: string ; ping?: string ; rel?: string ; shape?: string ; target?: string ; type?: string } ; article: HTMLElementTagGlobalAttributes ; aside: HTMLElementTagGlobalAttributes ; audio: HTMLElementTagGlobalAttributes & { autoplay?: string ; controls?: string ; crossorigin?: string ; loop?: string ; mediagroup?: string ; muted?: string ; preload?: string ; src?: string } ; b: HTMLElementTagGlobalAttributes ; base: HTMLElementTagGlobalAttributes & { href?: string ; target?: string } ; bdi: HTMLElementTagGlobalAttributes ; bdo: HTMLElementTagGlobalAttributes & { dir?: string } ; blockquote: HTMLElementTagGlobalAttributes & { cite?: string } ; body: HTMLElementTagGlobalAttributes & { alink?: string ; background?: string ; bgcolor?: string ; bottommargin?: string ; leftmargin?: string ; link?: string ; onafterprint?: string ; onbeforeprint?: string ; onbeforeunload?: string ; onblur?: string ; onerror?: string ; onfocus?: string ; onhashchange?: string ; onlanguagechange?: string ; onload?: string ; onmessage?: string ; onoffline?: string ; ononline?: string ; onpagehide?: string ; onpageshow?: string ; onpopstate?: string ; onredo?: string ; onresize?: string ; onstorage?: string ; onundo?: string ; onunload?: string ; rightmargin?: string ; text?: string ; topmargin?: string ; vlink?: string } ; br: HTMLElementTagGlobalAttributes & { clear?: string } ; button: HTMLElementTagGlobalAttributes & { autocomplete?: string ; autofocus?: string ; disabled?: string ; form?: string ; formaction?: string ; formenctype?: string ; formmethod?: string ; formnovalidate?: string ; formtarget?: string ; name?: string ; type?: string ; value?: string } ; canvas: HTMLElementTagGlobalAttributes & { height?: string ; moz-opaque?: string ; width?: string } ; caption: HTMLElementTagGlobalAttributes & { align?: string } ; cite: HTMLElementTagGlobalAttributes ; code: HTMLElementTagGlobalAttributes ; col: HTMLElementTagGlobalAttributes & { align?: string ; span?: string } ; colgroup: HTMLElementTagGlobalAttributes & { align?: string ; span?: string } ; data: HTMLElementTagGlobalAttributes & { value?: string } ; datalist: HTMLElementTagGlobalAttributes ; dd: HTMLElementTagGlobalAttributes & { nowrap?: string } ; del: HTMLElementTagGlobalAttributes & { cite?: string ; datetime?: string } ; details: HTMLElementTagGlobalAttributes & { open?: string } ; dfn: HTMLElementTagGlobalAttributes ; dialog: HTMLElementTagGlobalAttributes & { open?: string } ; div: HTMLElementTagGlobalAttributes ; dl: HTMLElementTagGlobalAttributes ; dt: HTMLElementTagGlobalAttributes ; em: HTMLElementTagGlobalAttributes ; embed: HTMLElementTagGlobalAttributes & { height?: string ; src?: string ; type?: string ; width?: string } ; fieldset: HTMLElementTagGlobalAttributes & { disabled?: string ; form?: string ; name?: string } ; figcaption: HTMLElementTagGlobalAttributes ; figure: HTMLElementTagGlobalAttributes ; footer: HTMLElementTagGlobalAttributes ; form: HTMLElementTagGlobalAttributes & { accept?: string ; accept-charset?: string ; action?: string ; autocapitalize?: string ; autocomplete?: string ; enctype?: string ; method?: string ; name?: string ; novalidate?: string ; target?: string } ; h1: HTMLElementTagGlobalAttributes ; h2: HTMLElementTagGlobalAttributes ; h3: HTMLElementTagGlobalAttributes ; h4: HTMLElementTagGlobalAttributes ; h5: HTMLElementTagGlobalAttributes ; h6: HTMLElementTagGlobalAttributes ; head: HTMLElementTagGlobalAttributes & { profile?: string } ; header: HTMLElementTagGlobalAttributes ; hgroup: HTMLElementTagGlobalAttributes ; hr: HTMLElementTagGlobalAttributes & { align?: string ; color?: string ; noshade?: string ; size?: string ; width?: string } ; html: HTMLElementTagGlobalAttributes & { manifest?: string ; version?: string ; xmlns?: string } ; i: HTMLElementTagGlobalAttributes ; iframe: HTMLElementTagGlobalAttributes & { allow?: string ; allowfullscreen?: string ; allowpaymentrequest?: string ; csp?: string ; height?: string ; importance?: string ; name?: string ; referrerpolicy?: string ; sandbox?: string ; seamless?: string ; src?: string ; srcdoc?: string ; width?: string } ; img: HTMLElementTagGlobalAttributes & { alt?: string ; crossorigin?: string ; decoding?: string ; height?: string ; importance?: string ; intrinsicsize?: string ; ismap?: string ; loading?: string ; referrerpolicy?: string ; sizes?: string ; src?: string ; srcset?: string ; usemap?: string ; width?: string } ; input: HTMLElementTagGlobalAttributes & { accept?: string ; alt?: string ; autocomplete?: string ; autofocus?: string ; checked?: string ; dirname?: string ; disabled?: string ; form?: string ; formaction?: string ; formenctype?: string ; formmethod?: string ; formnovalidate?: string ; formtarget?: string ; height?: string ; inputmode?: string ; list?: string ; max?: string ; maxlength?: string ; min?: string ; minlength?: string ; multiple?: string ; name?: string ; pattern?: string ; placeholder?: string ; readonly?: string ; required?: string ; size?: string ; src?: string ; step?: string ; type?: string ; value?: string ; width?: string } ; ins: HTMLElementTagGlobalAttributes & { cite?: string ; datetime?: string } ; kbd: HTMLElementTagGlobalAttributes ; label: HTMLElementTagGlobalAttributes & { for?: string ; form?: string } ; legend: HTMLElementTagGlobalAttributes ; li: HTMLElementTagGlobalAttributes & { type?: string ; value?: string } ; link: HTMLElementTagGlobalAttributes & { as?: string ; crossorigin?: string ; href?: string ; hreflang?: string ; importance?: string ; integrity?: string ; media?: string ; referrerpolicy?: string ; rel?: string ; sizes?: string ; title?: string ; type?: string } ; main: HTMLElementTagGlobalAttributes ; map: HTMLElementTagGlobalAttributes & { name?: string } ; mark: HTMLElementTagGlobalAttributes ; menu: HTMLElementTagGlobalAttributes ; meta: HTMLElementTagGlobalAttributes & { charset?: string ; content?: string ; http-equiv?: string ; name?: string ; scheme?: string } ; meter: HTMLElementTagGlobalAttributes & { form?: string ; high?: string ; low?: string ; max?: string ; min?: string ; optimum?: string ; value?: string } ; nav: HTMLElementTagGlobalAttributes ; noscript: HTMLElementTagGlobalAttributes ; object: HTMLElementTagGlobalAttributes & { archive?: string ; border?: string ; classid?: string ; codebase?: string ; codetype?: string ; data?: string ; declare?: string ; form?: string ; height?: string ; name?: string ; standby?: string ; tabindex?: string ; type?: string ; typemustmatch?: string ; usemap?: string ; width?: string } ; ol: HTMLElementTagGlobalAttributes & { compact?: string ; reversed?: string ; start?: string ; type?: string } ; optgroup: HTMLElementTagGlobalAttributes & { disabled?: string ; label?: string } ; option: HTMLElementTagGlobalAttributes & { disabled?: string ; label?: string ; selected?: string ; value?: string } ; output: HTMLElementTagGlobalAttributes & { for?: string ; form?: string ; name?: string } ; p: HTMLElementTagGlobalAttributes ; param: HTMLElementTagGlobalAttributes & { name?: string ; type?: string ; value?: string ; valuetype?: string } ; picture: HTMLElementTagGlobalAttributes ; pre: HTMLElementTagGlobalAttributes & { cols?: string ; width?: string ; wrap?: string } ; progress: HTMLElementTagGlobalAttributes & { max?: string ; value?: string } ; q: HTMLElementTagGlobalAttributes & { cite?: string } ; rb: HTMLElementTagGlobalAttributes ; rp: HTMLElementTagGlobalAttributes ; rt: HTMLElementTagGlobalAttributes ; ruby: HTMLElementTagGlobalAttributes ; s: HTMLElementTagGlobalAttributes ; samp: HTMLElementTagGlobalAttributes ; script: HTMLElementTagGlobalAttributes & { async?: string ; charset?: string ; crossorigin?: string ; defer?: string ; integrity?: string ; nomodule?: string ; nonce?: string ; referrerpolicy?: string ; src?: string ; text?: string ; type?: string } ; section: HTMLElementTagGlobalAttributes ; select: HTMLElementTagGlobalAttributes & { autocomplete?: string ; autofocus?: string ; disabled?: string ; form?: string ; multiple?: string ; name?: string ; required?: string ; size?: string } ; slot: HTMLElementTagGlobalAttributes & { name?: string } ; small: HTMLElementTagGlobalAttributes ; source: HTMLElementTagGlobalAttributes & { media?: string ; sizes?: string ; src?: string ; srcset?: string ; type?: string } ; span: HTMLElementTagGlobalAttributes ; strong: HTMLElementTagGlobalAttributes ; style: HTMLElementTagGlobalAttributes & { media?: string ; nonce?: string ; scoped?: string ; title?: string ; type?: string } ; sub: HTMLElementTagGlobalAttributes ; summary: HTMLElementTagGlobalAttributes ; sup: HTMLElementTagGlobalAttributes ; table: HTMLElementTagGlobalAttributes & { align?: string ; border?: string } ; tbody: HTMLElementTagGlobalAttributes & { align?: string } ; td: HTMLElementTagGlobalAttributes & { abbr?: string ; align?: string ; axis?: string ; bgcolor?: string ; colspan?: string ; headers?: string ; rowspan?: string } ; template: HTMLElementTagGlobalAttributes ; textarea: HTMLElementTagGlobalAttributes & { autocapitalize?: string ; autocomplete?: string ; autofocus?: string ; cols?: string ; dirname?: string ; disabled?: string ; form?: string ; inputmode?: string ; maxlength?: string ; minlength?: string ; name?: string ; placeholder?: string ; readonly?: string ; required?: string ; rows?: string ; spellcheck?: string ; wrap?: string } ; tfoot: HTMLElementTagGlobalAttributes & { align?: string } ; th: HTMLElementTagGlobalAttributes & { abbr?: string ; align?: string ; axis?: string ; bgcolor?: string ; colspan?: string ; headers?: string ; rowspan?: string ; scope?: string ; sorted?: string } ; thead: HTMLElementTagGlobalAttributes & { align?: string } ; time: HTMLElementTagGlobalAttributes & { datetime?: string } ; title: HTMLElementTagGlobalAttributes ; tr: HTMLElementTagGlobalAttributes & { align?: string } ; track: HTMLElementTagGlobalAttributes & { default?: string ; kind?: string ; label?: string ; src?: string ; srclang?: string } ; u: HTMLElementTagGlobalAttributes ; ul: HTMLElementTagGlobalAttributes & { compact?: string } ; var: HTMLElementTagGlobalAttributes ; video: HTMLElementTagGlobalAttributes & { autoplay?: string ; controls?: string ; crossorigin?: string ; height?: string ; loop?: string ; mediagroup?: string ; muted?: string ; poster?: string ; preload?: string ; src?: string ; width?: string } ; wbr: HTMLElementTagGlobalAttributes }

Map of HTML element tag attributes.

Remarks

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

Example

const getAttribute =
	<Tag extends keyof HTMLElementTagAttributeMap>(tag: Tag) =>
	(attribute: keyof HTMLElementTagAttributeMap[Tag]) => // ...

See

• HTMLElementTagGlobalAttributes
• ReadOnlyRecord

View source

---

HTMLElementTagGlobalAttributes

Ƭ HTMLElementTagGlobalAttributes: ReadOnlyRecord<string, string> & { accesskey?: string ; aria-activedescendant?: string ; aria-atomic?: string ; aria-autocomplete?: string ; aria-busy?: string ; aria-checked?: string ; aria-colcount?: string ; aria-colindex?: string ; aria-colspan?: string ; aria-controls?: string ; aria-current?: string ; aria-describedby?: string ; aria-details?: string ; aria-disabled?: string ; aria-dropeffect?: string ; aria-errormessage?: string ; aria-expanded?: string ; aria-flowto?: string ; aria-grabbed?: string ; aria-haspopup?: string ; aria-hidden?: string ; aria-invalid?: string ; aria-keyshortcuts?: string ; aria-label?: string ; aria-labelledby?: string ; aria-level?: string ; aria-live?: string ; aria-modal?: string ; aria-multiline?: string ; aria-multiselectable?: string ; aria-orientation?: string ; aria-owns?: string ; aria-placeholder?: string ; aria-posinset?: string ; aria-pressed?: string ; aria-readonly?: string ; aria-relevant?: string ; aria-required?: string ; aria-roledescription?: string ; aria-rowcount?: string ; aria-rowindex?: string ; aria-rowspan?: string ; aria-selected?: string ; aria-setsize?: string ; aria-sort?: string ; aria-valuemax?: string ; aria-valuemin?: string ; aria-valuenow?: string ; aria-valuetext?: string ; autocapitalize?: string ; class?: string ; contenteditable?: string ; contextmenu?: string ; dir?: string ; draggable?: string ; dropzone?: string ; exportparts?: string ; hidden?: string ; id?: string ; inputmode?: string ; is?: string ; itemid?: string ; itemprop?: string ; itemref?: string ; itemscope?: string ; itemtype?: string ; lang?: string ; onabort?: string ; onblur?: string ; oncanplay?: string ; oncanplaythrough?: string ; onchange?: string ; onclick?: string ; oncontextmenu?: string ; ondblclick?: string ; ondrag?: string ; ondragend?: string ; ondragenter?: string ; ondragleave?: string ; ondragover?: string ; ondragstart?: string ; ondrop?: string ; ondurationchange?: string ; onemptied?: string ; onended?: string ; onerror?: string ; onfocus?: string ; onformchange?: string ; onforminput?: string ; oninput?: string ; oninvalid?: string ; onkeydown?: string ; onkeypress?: string ; onkeyup?: string ; onload?: string ; onloadeddata?: string ; onloadedmetadata?: string ; onloadstart?: string ; onmousedown?: string ; onmouseenter?: string ; onmouseleave?: string ; onmousemove?: string ; onmouseout?: string ; onmouseover?: string ; onmouseup?: string ; onmousewheel?: string ; onpause?: string ; onplay?: string ; onplaying?: string ; onpointercancel?: string ; onpointerdown?: string ; onpointerenter?: string ; onpointerleave?: string ; onpointerlockchange?: string ; onpointerlockerror?: string ; onpointermove?: string ; onpointerout?: string ; onpointerover?: string ; onpointerup?: string ; onprogress?: string ; onratechange?: string ; onreadystatechange?: string ; onreset?: string ; onresize?: string ; onscroll?: string ; onseeked?: string ; onseeking?: string ; onselect?: string ; onshow?: string ; onstalled?: string ; onsubmit?: string ; onsuspend?: string ; ontimeupdate?: string ; onvolumechange?: string ; onwaiting?: string ; part?: string ; role?: string ; slot?: string ; spellcheck?: string ; style?: string ; tabindex?: string ; title?: string ; translate?: string }

Global HTML attributes.

Remarks

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

Example

const getAttribute = (attribute: keyof HTMLElementTagGlobalAttributes) => // ...

See

ReadOnlyRecord

View source

Iterables

IsomorphicIterable

Ƭ IsomorphicIterable<Item>: ReadOnly<AsyncIterable<Item> | Iterable<Item>>

Value might be an AsyncIterable or just an Iterable.

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

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

for (const item of iterable) {
	console.log(item); // Works
}

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

See

• @@iterator
• @@asyncIterator

Type parameters

Name	Type	Description
Item	unknown	Type of the items in the iterable.

View source

---

IsomorphicIterableItem

Ƭ 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

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

See

IsomorphicIterable

Type parameters

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

View source

Number

Digit

Ƭ 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

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

See

Enumerate

View source

---

Enumerate

Ƭ 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

type From0To10 = Enumerate<10>;

Type parameters

Name	Type	Description
To	extends number	Last number of the union (starts at 0).
Accumulator	extends number[] = []	Accumulator for the recursion (for internal use).

View source

---

Numeric

Ƭ 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

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

View source

---

Radix

Ƭ 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

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

See

Range

View source

---

Range

Ƭ 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

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

See

Enumerate

Type parameters

Name	Type
From	extends number
To	extends number

View source

Object

Empty

Ƭ Empty: EmptyArray | EmptyRecord | EmptyString

Empty array, object or string.

Remarks

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

Example

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

See

• EmptyArray
• EmptyRecord
• EmptyString

View source

---

EmptyRecord

Ƭ EmptyRecord: ReadOnlyRecord<PropertyKey, never>

Empty record (object).

Remarks

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

Example

const emptyRecord: EmptyRecord = {};

See

ReadOnlyRecord

View source

---

Entry

Ƭ Entry<Key, Value>: readonly [key: Key, value: 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

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

Type parameters

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

View source

---

EntryKey

Ƭ EntryKey<Input>: First<Input>

Key of an Entry.

Remarks

Util type to get the key of an Entry.

Example

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

See

• Entry
• First

Type parameters

Name	Type	Description
Input	extends Entry	Entry type.

View source

---

EntryOf

Ƭ EntryOf<Input>: Entry<KeyOf<Input>, ValueOf<Input>>

Object or array Entry.

Remarks

Get the Entry type out of an object or array.

Example

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

See

• Entry
• KeyOf
• ReadOnlyCollection
• ValueOf

Type parameters

Name	Type	Description
Input	extends ReadOnlyCollection	Array or record type.

View source

---

EntryValue

Ƭ EntryValue<Input>: Second<Input>

Value of an Entry.

Remarks

Util type to get the value of an Entry.

Example

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

See

• Entry
• Second

Type parameters

Name	Type	Description
Input	extends Entry	Entry type.

View source

---

KeyOf

Ƭ KeyOf<Input>: Input extends ArrayLike ? NeverFallback<Defined<Exclude<Partial<Input>["length"], Input["length"]>>, number> : `${Exclude<keyof Input, symbol>}`

Generic key for either object or array.

Remarks

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

Example

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

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

See

ReadOnlyCollection

Type parameters

Name	Type	Description
Input	extends ReadOnlyCollection	The input ReadOnlyCollection.

View source

---

NotEmpty

Ƭ 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

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

See

Empty

Type parameters

Name	Type	Description
Type	extends ArrayLike | object | string	The type to check.

View source

---

ReadOnly

Ƭ ReadOnly<Input>: Input extends Readonly<ReadonlyMap<infer Key, infer Value>> ? Readonly<ReadonlyMap<ReadOnly<Key>, ReadOnly<Value>>> : Input extends Readonly<ReadonlySet<infer Item>> ? Readonly<ReadonlySet<ReadOnly<Item>>> : Input extends readonly [] ? readonly [] : Input extends readonly [infer Head, …(infer Tail)] ? readonly [ReadOnly<Head>, …ReadOnly<Tail>] : Input extends ReadonlyArray<infer Item> ? ReadonlyArray<ReadOnly<Item>> : Input extends Function ? Input : Input extends object ? { readonly [Property in keyof Input]: ReadOnly<Input[Property]> } : Input

Read-only deep any Input.

Remarks

This type makes any Input read-only recursively, including nested objects and arrays, Sets, Maps, and functions.

Example

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

Type parameters

Name	Description
Input	The type to make read-only.

View source

---

ReadOnlyCollection

Ƭ ReadOnlyCollection<Item>: ArrayLike<Item> | ReadOnlyRecord<PropertyKey, Item>

Read-only collection (ArrayLike or ReadOnlyRecord).

Remarks

Read-only type union of ArrayLike or ReadOnlyRecord.

Example

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

See

• ArrayLike
• ReadOnlyRecord

Type parameters

Name	Type	Description
Item	unknown	Type of the items in the collection.

View source

---

ReadOnlyRecord

Ƭ 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, plus it recursively makes all the values in the record read-only.

Example

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

See

ReadOnly

Type parameters

Name	Type	Description
Key	extends PropertyKey = PropertyKey	Type of the keys in the record.
Value	unknown	Type of the values in the record.

View source

---

ValueOf

Ƭ ValueOf<Input>: Input[KeyOf<Input> & keyof Input]

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

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

See

ReadOnlyCollection

Type parameters

Name	Type	Description
Input	extends ReadOnlyCollection	Type of the collection.

View source

RegExp

RegularExpression

Ƭ 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

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

See

• RegularExpressionFlags
• Regular Expressions

View source

---

RegularExpressionFlags

Ƭ RegularExpressionFlags: `${EmptyString | “g”}${EmptyString | “i”}${EmptyString | “m”}${EmptyString | “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

const flags1: RegularExpressionFlags = "u";
const flags2: RegularExpressionFlags = "gu";
const flags3: RegularExpressionFlags = "iu";
const flags4: RegularExpressionFlags = "giu";

See

Regular Expressions

View source

String

Empty

Ƭ Empty: EmptyArray | EmptyRecord | EmptyString

Empty array, object or string.

Remarks

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

Example

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

See

• EmptyArray
• EmptyRecord
• EmptyString

View source

---

EmptyString

Ƭ EmptyString: ""

Empty string.

Remarks

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

Example

const emptyString: EmptyString = "";

View source

---

First

Ƭ First<Input>: Input[0]

First value of an ArrayLike.

Remarks

Type of the first item of an ArrayLike, mainly here to avoid magic numbers.

Example

const array = ["🟢", "🟩", "💚"];
const first: First<typeof array> = "🟢";

See

• ArrayLike
• InitialAndLast

Type parameters

Name	Type	Description
Input	extends ArrayLike	The input ArrayLike.

View source

---

Head

Ƭ Head<Input>: First<HeadAndTail<Input>>

Initial value of an ArrayLike.

Remarks

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

Example

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

See

• ArrayLike
• First
• HeadAndTail

Type parameters

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

View source

---

HeadAndTail

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

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

See

• ArrayLike
• EmptyArray
• EmptyString
• Head
• Maybe
• Tail

Type parameters

Name	Type	Description
Input	extends ArrayLike	Input ArrayLike.

View source

---

Initial

Ƭ Initial<Input>: First<InitialAndLast<Input>>

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

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

See

• ArrayLike
• First
• InitialAndLast

Type parameters

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

View source

---

InitialAndLast

Ƭ InitialAndLast<Input>: Input extends readonly […(infer InitialItems), infer LastItem] ? readonly [initial: InitialItems, last: LastItem] : Input extends EmptyArray | EmptyString ? readonly [initial: Input, last: undefined] : Input extends `${infer FirstCharacter}${infer RestOfString}` ? readonly [initial: `${RestOfString extends EmptyString ? EmptyString : FirstCharacter}${Head<InitialAndLast<RestOfString>>}`, last: `${RestOfString extends EmptyString ? FirstCharacter : Last<RestOfString>}`] : readonly [initial: Input, last: 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

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

See

• ArrayLike
• EmptyArray
• EmptyString
• Head
• Initial
• Last
• Maybe

Type parameters

Name	Type	Description
Input	extends ArrayLike	Input ArrayLike.

View source

---

Last

Ƭ Last<Input>: Second<InitialAndLast<Input>>

Last value of an ArrayLike.

Remarks

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

Example

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

See

• ArrayLike
• InitialAndLast
• Second

Type parameters

Name	Type	Description
Input	extends ArrayLike	The input ArrayLike.

View source

---

NotEmpty

Ƭ 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

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

See

Empty

Type parameters

Name	Type	Description
Type	extends ArrayLike | object | string	The type to check.

View source

---

Second

Ƭ Second<Input>: Input[1]

Second value of an ArrayLike.

Remarks

Type of the Second item of an ArrayLike, manly here to avoid magic numbers.

Example

const array = ["🟢", "🟩", "💚"];
const second: Second<typeof array> = "🟩";

See

• ArrayLike
• InitialAndLast

Type parameters

Name	Type	Description
Input	extends ArrayLike	The input ArrayLike.

View source

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Tagger

Ƭ Tagger<Output, Expressions>: Function<readonly [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

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

See

• Function
• ReadOnly
• ReadOnlyArray

Type parameters

Name	Type	Description
Output	string	Type of the output value.
Expressions	extends ReadOnlyArray = ReadOnlyArray	Type of the expressions.

View source

---

Tail

Ƭ Tail<Input>: Second<HeadAndTail<Input>>

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

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

See

• ArrayLike
• HeadAndTail
• Second

Type parameters

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

View source