Event Emitter

import { EventEmitter } from "https://deno.land/x/event_emitter/mod.ts"

// Define what events you want to use. EventEmitter will provide IntelliSense support based on your event types.
interface ConnectionEvents {
    connected: () => void
    disconnected: (reason: string) => void
    error: (errorCode: number, reason?: string) => typeof Error
    handshake: (interval: number) => Promise<boolean> // Asynchronous callback
}

class Connection extends EventEmitter<ConnectionEvents> {
    // Your own class
}

const conn = new Connection()

// EventEmitter#once attaches new listener and deletes it after first execution.
conn.once('connected', () => console.info('Successfully connected!'))

// EventEmitter#on attaches listener that will work continuously until you delete it manually using EventEmitter#off method.
conn.on('error', (code, msg) => console.error(`Caught error: [${code}] ${msg}`))



// Trigger your listener(s) by emitting signal somewhere in your code:
conn.emit('error', 429, 'rate limit')

import { EventEmitter } from "https://deno.land/x/event_emitter/mod.ts"

// let's this time increase maxListeners limit to 20 cause why not.
// Normally it's blocked on 5 to prevent memory leaks in poorly made codes.
const emitter = new EventEmitter(20)

// You cannot be fully sure of received args in this case (no interface).
emitter.on('hello', (name?: string) => {
    if (name && typeof name === 'string') console.log(`Hello ${name}!`)
    else console.warn(`Received invalid arg. Expected "string" but received "${typeof name}".`)
})

emitter.emit('hello', 'David') // Output: Hello David!

emitter.emit('hello', 24) // Output: Received invalid arg. (...)

emitter.off('hello') // Deletes entire event & all its listeners.
// EventEmitter#off returns boolean signal to inform about result.

emitter.emit('hello', 'David') // No reaction