Typescript advanced built-in types (utility types)

Partial

Make all properties in T optional.

type t = Partial<{a: string; b: number}>;
// {a?: string; b?: number}

Make all properties in T required.

type t = Required<{a?: string; b?: number}>;
// {a: string; b: number}

Make all properties in T readonly.

type t = Readonly<{a: string; b: number; c?: boolean}>;
// {readonly a: string; readonly b: number; readonly c?: boolean}

From T, pick a set of properties whose keys are in the union K.

type t = Pick<{a: string; b: number; c?; boolean}, 'a' | 'c'>;
// {a: string; c?; boolean}

Construct a type with a set of properties K of type T.

type Demo = {...};
type t = Record<'a' | 'b' | 'c', Demo>;
// {a: Demo; b: Demo; c: Demo}

Exclude from T those types that are assignable to U.

type t = Exclude<'a' | 'b' | 'c' | 'd', 'b' | 'c' | 'x' | 'y'>;
// 'a' | 'd'

Extract from T those types that are assignable to U.

type t = Extract<'a' | 'b' | 'c' | 'd', 'b' | 'c' | 'x' | 'y'>;
// 'b' | 'c'

Exclude null and undefined from T.

type t = NonNullable<'a' | string | number | undefined>;
// 'a' | string | number

Obtain the parameters of a function type in a tuple.

type t = Parameters<(a: string, b: number) => void>;
// [string, number]

Obtain the return type of a function type.

type t = ReturnType<(a: string, b: number) => string>;
// string

Obtain the return type of a constructor function type.

type t = InstanceType<typeof C>;
// C