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HTML / CSS / JS

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

// Branded primitive types
type UserId    = Brand<number, "UserId">;
type OrderId   = Brand<number, "OrderId">;
type Email     = Brand<string, "Email">;
type USD       = Brand<number, "USD">;
type EUR       = Brand<number, "EUR">;

// Factory functions that create branded values
function asUserId(n: number):  UserId  { return n as UserId; }
function asOrderId(n: number): OrderId { return n as OrderId; }

function parseEmail(raw: string): Email {
    if (!/^[^@]+@[^@]+\.[^@]+$/.test(raw)) {
        throw new Error(`Invalid email: ${raw}`);
    }
    return raw as Email;
}

// Functions that only accept the correct branded type
function fetchUser(id: UserId): Promise<string> {
    return Promise.resolve(`User ${id}`);
}

const userId  = asUserId(1);
const orderId = asOrderId(1);

fetchUser(userId);  // OK
// fetchUser(orderId);  // Error: OrderId is not assignable to UserId
// fetchUser(1);        // Error: number is not assignable to UserId

// Currency brands prevent mixing
function addUSD(a: USD, b: USD): USD { return (a + b) as USD; }

const price: USD  = 19.99 as USD;
const tax: USD    = 1.60  as USD;
const total       = addUSD(price, tax);

const eur: EUR = 18.00 as EUR;
// addUSD(price, eur); // Error: EUR is not assignable to USD