API reference / @node-ts/bus-messages / defineEvent

Function: defineEvent()

function defineEvent<TName>(name, options?): <TData>() => MessageDefinition<DefinedMessage<TName, TData>, TData>;

Defined in: packages/bus-messages/src/define-event.ts:29

Declares an event, something that happened that is published to every subscriber, without writing a class. The definition creates events from their fields, and is used anywhere a message class is: handlerFor, startedBy and when. The events it creates are plain objects, with $name and $version added.

The name comes first and the fields second, so the name's literal type is inferred. Run bus generate-message-types (in @node-ts/bus-cli) to have Dates, Maps, Sets, bigints and classes in the fields restored when the event is received.

Type Parameters

Type Parameter
TName extends string

Parameters

Parameter	Type	Description
name	TName	the $name of the event, which routes it, so make it unique
options?	DefineMessageOptions	the $version of the event's contract

Returns

a function that takes the type of the event's fields as its type argument, and returns the definition

<TData>() => MessageDefinition<DefinedMessage<TName, TData>, TData>

Example

export const OrderPlaced = defineEvent('@my-org/orders/order-placed')<{
  orderId: string
  placedAt: Date
}>()
export type OrderPlaced = MessageOf<typeof OrderPlaced>

await bus.publish(OrderPlaced({ orderId: '1', placedAt: new Date() }))
handlerFor(OrderPlaced, async orderPlaced => orderPlaced.placedAt.getTime())