emitter.js

/*
Emitter
*/"use strict"

var indexOf = require("mout/array/indexOf"),
    forEach = require("mout/array/forEach")

var prime = require("./index"),
    defer = require("./defer")

var slice = Array.prototype.slice;

var Emitter = prime({

    constructor: function(stoppable){
        this._stoppable = stoppable
    },

    on: function(event, fn){
        var listeners = this._listeners || (this._listeners = {}),
            events = listeners[event] || (listeners[event] = [])

        if (indexOf(events, fn) === -1) events.push(fn)

        return this
    },

    off: function(event, fn){
        var listeners = this._listeners, events
        if (listeners && (events = listeners[event])){

            var io = indexOf(events, fn)
            if (io > -1) events.splice(io, 1)
            if (!events.length) delete listeners[event];
            for (var l in listeners) return this
            delete this._listeners
        }
        return this
    },

    emit: function(event){
        var self = this,
            args = slice.call(arguments, 1)

        var emit = function(){
            var listeners = self._listeners, events
            if (listeners && (events = listeners[event])){
                forEach(events.slice(0), function(event){
                    var result = event.apply(self, args)
                    if (self._stoppable) return result
                })
            }
        }

        if (args[args.length - 1] === Emitter.EMIT_SYNC){
            args.pop()
            emit()
        } else {
            defer(emit)
        }

        return this
    }

})

Emitter.EMIT_SYNC = {}

module.exports = Emitter