TS#1 Type-safe publish event function

Tony Ngan — Sun, 06 Nov 2022 10:08:00 +0000

When we design an event, the descriptors are simply the type and payload, where payload is composed of the properties describing what's happened in the system.

enum MyEvent {
  FOO = 'FOO',
  BAR = 'BAR'
}

interface MyEventPayload {
  [MyEvent.FOO]: {
    prop1: string;
    prop2: string;
  }
}

async function sendEvent<T extends keyof MyEventPayload>(type: T, payload: MyEventPayload[T]): Promise<void> {
  // implementation
}

// @ts-expect-error
sendEvent();
// @ts-expect-error
sendEvent(MyEvent.FOO);
// @ts-expect-error
sendEvent(MyEvent.FOO, {});
// @ts-expect-error
sendEvent(MyEvent.FOO, { prop1: 'x', prop2: 'y', prop3: 'z' });

// works!
sendEvent(MyEvent.FOO, { prop1: 'x', prop2: 'y' });

By taking advantage of the generics, we can easily construct a type-safe function where the type of arguments are dependent on each other.

DEV Community: Tony Ngan

TS#1 Type-safe publish event function