TypeScript Strict Mode in Enterprise Applications: Eliminating Runtime Bugs

// Branded Nominal Types
export type UserId = string & { readonly __brand: unique symbol };
export type OrderId = string & { readonly __brand: unique symbol };

// Discriminated Union of Order States
export type OrderStatus = 
  | { status: 'PENDING'; invoiceUrl: string }
  | { status: 'PAID'; transactionId: string; paidAt: Date }
  | { status: 'FAILED'; errorCode: string; retryCount: number };

// Exhaustiveness checking utility
export function assertNever(x: never): never {
  throw new Error(`Unexpected object encountered in state machine: ${JSON.stringify(x)}`);
}

export function renderOrderStatusBadge(order: OrderStatus): string {
  switch (order.status) {
    case 'PENDING':
      return `Awaiting payment: ${order.invoiceUrl}`;
    case 'PAID':
      return `Completed via ${order.transactionId}`;
    case 'FAILED':
      return `Failed with code ${order.errorCode} (Attempt ${order.retryCount})`;
    default:
      return assertNever(order); // Compile error if a new status is added without handling!
  }
}