go get github.com/fdanismaz/go-events/event

The event listener starts as the github.com/fdanismaz/go-events/event is imported because the package has an init function which starts the listener until you explicitly call event.Stop() function.

To subscribe to an event you can use the Subscribe or SubscribeMultiple functions. The Subscribe function subscribe your callback function to a specific event, SubscribeMultiple function, on the other hand, subscribe your callback function to multiple events, meaning that whenever any of the subscribed event is emitted, your callback function will be executed.

var UserCreated event.Type = "user-created"

handlerId := event.Subscribe(UserCreated, func(args ...interface{}) {
    id := args[0].(int)
    name := args[1].(string)
    
    fmt.Printf("A new user is created. ID: %d, Name: %s\n", id, name)
})

Both the Subscribe and the SubscribeMultiple creates returns a handler id for your callback function. When you want to unsubscribe from a specific event or multiple events you can use Unsubscribe or UnsubscribeMultiple.

event.Unsubscribe(UserCreated, handlerId)

When you emit an event, an event object including the event type, and the arguments is created. That event object is written to the event channel which is catched by the event listener. The event listener executes each registered handler function for that event type in a separate go routine.

event.Emit(UserCreated, userId, userName)