object-transforms

`Record<K, V>`

Creates an object type whose keys come from the union K and whose values all have type V. Useful for lookup tables, dictionaries, and enum-keyed maps.

Definition

type Record<K extends keyof any, V> = { [P in K]: V }

Usage patterns

Pattern	Purpose
Record<string, T>	Loose dictionary / index signature
Record<'a' \| 'b', T>	Exhaustive map — every listed key required
Record<Enum, T>	Force a value for every enum member
Partial<Record<K, V>>	Sparse dictionary — keys optional

Examples

type Roles = 'admin' | 'user' | 'guest';
type Permissions = Record<Roles, string[]>;

TS will error if any of the three role keys is missing

const cache: Record<string, User> = {};
cache['42'] = user;

Basic string-keyed dictionary — every access returns User (or undefined with noUncheckedIndexedAccess)

type PageMap = Record<number, string>;

Numeric-keyed lookup — TS also allows number keys as strings at runtime

type SparseMap = Partial<Record<'a' | 'b' | 'c', number>>;

Now each key is optional: { a?; b?; c? }

Gotcha

With `Record` without noUncheckedIndexedAccess, accessing a missing key returns V rather than V | undefined — hiding real bugs. Prefer enabling that flag or narrow K to a finite union.

Related utility types

Pick<T, K>

Builds a new type containing only the properties from T whose keys are in the union K. Ideal for narrowing large interfaces to the subset a function or component actually needs.

Partial<T>

Constructs a type where every property of T is set to optional. Useful for representing update payloads, patch objects, and configuration overrides where all fields may be omitted.

Readonly<T>

Marks every property of T as readonly, preventing reassignment after construction. Only enforced at compile-time — the underlying object is still mutable at runtime.

Omit<T, K>

Constructs a type by removing the properties in K from T. Unlike Pick, its K is not constrained to keyof T, so extra keys are silently ignored.

Required<T>

Removes optionality from every property of T, producing a type where all fields must be present. The -? mapping modifier strips the ? flag from every key.

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