Brand

Brands a base type T with a phantom tag B to create a nominal type.

Two Brand<string, 'UserId'> and Brand<string, 'Email'> are structurally identical strings at runtime, but TypeScript treats them as distinct types at the call site — preventing accidental mix-ups.

Use a const-assertion cast at the creation boundary:

type UserId = Brand<string, 'UserId'>;
const toUserId = (s: string): UserId => s as UserId;

Available since v3.0.0

Import

import type { Brand } from '@helpers4/type';

Type Definition

type Brand<T, B extends string> = T & { readonly __brand: B }

Examples

Brand

type Meter = Brand<number, 'Meter'>;
type Second = Brand<number, 'Second'>;

declare function speed(distance: Meter, time: Second): number;
const d = 100 as Meter;
const t = 5 as Second;
speed(d, t);   // ✅
speed(t, d);   // ✗ Type error — args swapped

Source

View source on GitHub