Custom event handling in Golang

EventHandler.go

package main

import (
	"fmt"
	"time"
)

type EventType interface {
	AddEventListener(string, func(interface{}))
	Trigger(string, interface{})
}

type CustomEvent struct {
	listeners map[string][]func(interface{})
}

var event EventType

func NewCustomEvent() EventType {
	if event == nil {
		event = &CustomEvent{listeners: map[string][]func(interface{}){}}
	}
	return event
}

func (ce *CustomEvent) AddEventListener(eventType string, hanlder func(interface{})) {
	if hanlders, ok := ce.listeners[eventType]; !ok {
		ce.listeners[eventType] = []func(interface{}){hanlder}
	} else {
		ce.listeners[eventType] = append(hanlders, hanlder)
	}
}

func (ce *CustomEvent) Trigger(eventType string, data interface{}) {
	if hanlders, ok := ce.listeners[eventType]; ok {
		for _, handler := range hanlders {
			handler(data)
		}
	}
}

main.go

package main

import (
	"fmt"
	"github.com/rbrahul/eventhandler" // tried in locally with go mod replace. didn't publish to github
)

func main() {
	var myCustomEvent EventType = NewCustomEvent()

	myCustomEvent.AddEventListener("send_email", func(data interface{}) {
		fmt.Printf("Verifying email adress:%v before sending\n", data)
	})

	myCustomEvent.AddEventListener("send_email", func(data interface{}) {
		fmt.Println("Sending mail to:", data)
	})

	fmt.Println("Going to trigger send_mail")
	time.Sleep(2 * time.Second)
	myCustomEvent.Trigger("send_email", "my_awesome_email_address@gmail.com")
}