interview.js

function EventEmitter () {
    
    events = {}

    function publish(type, payload) {
        callbacks = events[type]
        callbacks.forEach(c => {
            c(payload)
        })
    }

    function subscribe(type, callback) {
        events[type].push(callback)
    } 

    function unsubscribe(type, callback) {
        callbacks = events[type]
        events[type] = callbacks.filter(c => !c.compare(callback))
    }
}

new EventEmitter('login', () => {

})