errors-as-values

An expected business failure is a value: the aggregate returns it in a Result, and every caller sees, in the signature, what can go wrong. Exceptions stay for bugs.

❌ Avoid: src/ordering/domain/aggregates/order.aggregate.ts

export class Order extends AggregateRoot<OrderId> {
	place(total: number): void {
		if (total <= 0) {
			throw new InvalidTotal({ total });
		}
	}
}

✅ Prefer: src/ordering/domain/aggregates/order.aggregate.ts

export class Order extends AggregateRoot<OrderId> {
	place(total: number): Result<void, InvalidTotal> {
		if (total <= 0) {
			return err(new InvalidTotal({ total }));
		}
		return ok();
	}
}

What it checks

• Every public method of a class that extends AggregateRoot or Entity returns a Result, even when its return type is inferred. Getters, static methods, toSnapshot and equals are left out.
• No DomainError is thrown, anywhere in the project.

Why

A thrown error is invisible in a signature: the caller does not know it has to handle it, and forgets. A Result lists every failure in the type, and TypeScript makes the caller deal with it. Requiring it on every public method of an aggregate also keeps the API honest: a method that changes state says whether it worked, and reads are getters.

A read that needs parameters, such as canShip(date), returns ok(…), or moves to a DomainService when it involves more than the aggregate.

What it reports

src/ordering/domain/aggregates/order.aggregate.ts:2
  errors-as-values: Order.place must return a Result: expose reads as getters and return business failures as values.

src/ordering/domain/aggregates/order.aggregate.ts:4
  errors-as-values: A DomainError is thrown: return it in a Result instead.

Turn it off

rules: { "errors-as-values": "off" }

See also

• building-blocks-only, which keeps extends Error out of the domain