branded-types.ts

type Branded<T, U extends string> = T & { [Symbol.species]: U };
// if targeting ES5, change to:
// type Branded<T, U> = T & { ['Brand']: U };

// FOO
type FooId = Branded<number, 'FooId'>;

// BAR
type BarId = Branded<number, 'BarId'>;

// Usage Demo
let fooId: FooId;
let barId: BarId;

// Safety!
fooId = barId; // error
barId = fooId; // error

// Newing up
fooId = 1 as FooId;
barId = 2 as BarId;

// Both types are compatible with the base
let n: number;
n = fooId;
n = barId;