可用于小程序的发布订阅模式，主要用于跨页面通讯

event.js

class Event {
    on (event, fn, ctx) {
        if (typeof fn != "function") {
            console.error('fn must be a function')
            return
        }

        this._stores = this._stores || {}

        ;(this._stores[event] = this._stores[event] || []).push({cb: fn, ctx: ctx})
    }
    emit (event) {
        this._stores = this._stores || {}
        var store = this._stores[event], args
        if (store) {
            store = store.slice(0)
            args = [].slice.call(arguments, 1)
            for (var i = 0, len = store.length; i < len; i++) {
                store[i].cb.apply(store[i].ctx, args)
            }
        }
    }
    off (event, fn) {
        this._stores = this._stores || {}
        // all
        if (!arguments.length) {
            this._stores = {}
            return
        }
        // specific event
        var store = this._stores[event]
        if (!store) return
        // remove all handlers
        if (arguments.length === 1) {
            delete this._stores[event]
            return
        }
        // remove specific handler
        var cb
        for (var i = 0, len = store.length; i < len; i++) {
            cb = store[i].cb
            if (cb === fn) {
                store.splice(i, 1)
                break
            }
        }
        return
    }
}

example.js

/**
 * 使用示例
 * /

// app.js

const Event = require('./utils/event')
App({
    event: new Event(),
    ...
})

// subsPage.js

let app = getApp()
Page({
    onLoad: function(){
        app.event.on('eventName',this.triggerEvent, this)
    },
    onUnload: function(){
        // remove all
        // app.event.off()
        // remove all callbacks
        app.event.off('eventName')
        // remove specific callbacks
        // app.event.off('eventName', this.triggerEvent)
    },
    triggerEvent: function(args) {
        ...
    },
    ...
})

// emitPage.js

let app = getApp()
Page({
    emitFunc: function() {
        ... 
        app.event.emit('eventName', arg)
    },
    ...
})