Type Helpers

Utility functions for working with type operations.

Functions

Function	Description
Brand	Brands a base type `T` with a phantom tag `B` to create a nominal type.
DeepGet	Resolves the value type at a given `Path` within `T`.
DeepPartial	Recursively makes all properties of T optional, including nested objects and array elements.
DeepSet	Produces the type of `T` after replacing the value at `Path` with `V`.
DeepWritable	Recursively removes `readonly` from all properties of T, including nested objects, array elements, and tuple positions.
isDirectInstanceOf	native JS value.constructor === Foo (ES1)
isFinite / isFiniteNumber	native JS Number.isFinite(value) (ES2015)
isHtmlElement / isUrlInstance / isUrlSearchParams	native JS value instanceof HTMLElement / URL / URLSearchParams (Web API)
isInfinite	native JS value === Infinity || value === -Infinity / !Number.isFinite(value) && !Number.isNaN(value) (ES2015)
isInteger	native JS Number.isInteger(value) (ES2015)
isNaN	native JS Number.isNaN(value) (ES2015)
isSafeInteger	native JS Number.isSafeInteger(value) (ES2015)
isSet (Set data structure)	native JS value instanceof Set (ES2015)
isWeakMap / isWeakSet / isWeakRef	native JS value instanceof WeakMap / WeakSet / WeakRef (ES2015 / ES2021)
KeysOfType	Extracts the keys of `T` whose values extend `V`.
Maybe	Type for values that can be T, undefined, or null.
Nullable	Adds `null` to a type (`T | null`).
Nullish	Adds `null` and `undefined` to a type (`T | null | undefined`).
OmitByValue	Constructs a type by omitting all entries of `T` whose values extend `V`.
OptionalKeys	Extracts the optional keys of an object type `T`.
PickByValue	Constructs a type by picking all entries of `T` whose values extend `V`.
Prettify	Flattens an intersection type into a single readable object type.
RequiredKeys	Extracts the required (non-optional) keys of an object type `T`.
TypedArrays (isInt8Array, isFloat32Array, ...)	native JS value instanceof Int8Array / Float32Array / ... (ES2015)
UnionToIntersection	Converts a union type to an intersection type: `A | B | C` → `A & B & C`.
ValueOf	Produces a union of all value types of an object type `T`.