Simple event emitter for Javascript Constructor

event.js

var customEvent = function(){
    var self =this;
    self.events = {}
    self.on = function (event, listener) {
        if (typeof self.events[event] !== 'object') {
            self.events[event] = []
        }
        self.events[event].push(listener)
    }

    self.removeListener = function (event, listener) {
        let idx

        if (typeof self.events[event] === 'object') {
            idx = self.events[event].indexOf(listener)

            if (idx > -1) {
                self.events[event].splice(idx, 1)
            }
        }
    }

    self.emit = function (event) {
        var i, listeners, length, args = [].slice.call(arguments, 1);

        if (typeof self.events[event] === 'object') {
            listeners = self.events[event].slice()
            length = listeners.length

            for (i = 0; i < length; i++) {
                listeners[i].apply(self, args)
            }
        }
    }

    self.once = function (event, listener) {
        self.on(event, function g () {
            self.removeListener(event, g)
            listener.apply(self, arguments)
        })
    }
}


/*
var Parent = function(){
    this.channel = new customEvent();
    // rest of you logic
}

var myParent = new Parent();
myParent.channel.on("alarm", function(data){
    console.log("Alarm: ",data);
});
myParent.channel.emit("alarm",{type:"fire"});

*/