Nodejs监听器

     Node事件监听1、将自定义事件添加到JavaScript对象Emit（eventName，[args]）函数触发eventName事件。如果想直接把时间添加到自己的javascript对象:1>.调用events.EventEmitter.call(this)来对象中继承EventEmitter功能2>.把events.EventEmitter.prototype添加到对象的原型中2、把事件监听器添加到对象1>  .addListener(eventName,callback):将回调函数附加到对象的监听器中。每当eventName事件被触发时，回调函数就被放置在事件队列中执行。2>  .on(eventName,callback)：同上。3>  .once(eventName,callback)：只有eventName事件第一次被触发时，回调函数才被放置在事件队列中执行。事件监听器实例：var http = require("http");var events = require("events");  //引用events模块http.createServer(function(request,response){response.writeHead(200,{"Conetnt-Type":"text/html;charset = utf-8"});if(request.url !== "/favicon.ico")  //清除第二次访问{var account = new Account();//把事件监听器添加到对象account.addListener("balanceChanged",displayBalance);account.addListener("balanceChanged",checkOverdraw);account.addListener("balanceChanged",function(){checkGoal(this,1000);});account.deposit(220);account.deposit(320);account.deposit(600);account.withdraw(1200);response.end();}}).listen(8000);console.log("start running......");//自定义事件function Account(){this.balance = 0;//继承EventEmitter功能events.EventEmitter.call(this);//定义两个方法this.deposit = function(amount){this.balance += amount;//触发balanceChanged事件this.emit("balanceChanged"); };this.withdraw = function (amount) {this.balance -= amount;this.emit("balanceChanged");};}//把events.EventEmitter.prototype添加到对象的原型中Account.prototype.__proto__ = events.EventEmitter.prototype;//显示余额function displayBalance() {console.log("Account balance:$%d",this.balance);}//判断是否余额大于0function checkOverdraw(){if(this.balance<0){console.log("Account overdrawn!!!");}}function checkGoal(acc,goal){if(this.balance>goal){console.log("Goal Achieved!");}} <img src="http://img.blog.csdn.net/20160913233548556?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />回调函数1、 向回调函数传递额外的参数：在一个匿名函数中实现该函数，再用来自匿名函数的参数调用回调函数2、 在回调中实现闭包：某个回调函数需要访问父函数的作用域的变量，就需要提供闭包。3、 使用一部函数时，如果两个函数都在事件队列上，则无法保证他们的运行顺序。

   解决方案是：

让来自异步函数的回调再次调用该函数，指导没有更多的工作要做，以链式回调。1. 匿名函数中实现参数var http = require("http");var events = require("events");http.createServer(function(request,response){response.writeHead(200,{"Conetnt-Type":"text/html;charset = utf-8"});if(request.url !== "/favicon.ico"){ var show = new CarShow();show.on("sawCar",logCar);//匿名函数中实现参数show.on("sawCar",function(make){var colors = ["red","blue","black"];var color = colors[Math.floor(Math.random()*3)];logColorCar(make,color);});show.seeCar("1");show.seeCar("2");show.seeCar("3");show.seeCar("4");show.seeCar("5");show.seeCar("6");response.end();}}).listen(8000);console.log("start running......");function CarShow() {events.EventEmitter.call(this);//匿名函数中实现参数this.seeCar = function(make){this.emit("sawCar",make);};}CarShow.prototype.__proto__ =  events.EventEmitter.prototype;function logCar(make) {console.log("Saw a "+make);}function logColorCar(make,color){console.log("Saw a %s %s ",color,make);} <img src="http://img.blog.csdn.net/20160913233556275?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />2、链式回调函数var http = require("http");var cars = ["Ferrari","Porsche","Bugatti","1","2"];http.createServer(function(request,response){response.writeHead(200,{"Content-Type":"text/html;charset = utf-8"});if(request.url !== "/favicon.ico"){//链式回调函数logCars(cars); response.end();}}).listen(8000);console.log("start running......");function logCar(car,callback) {console.log("Saw a %s",car)if(cars.length){process.nextTick(function() {callback();});}}function logCars(cars) {var car = cars.pop();logCar(car,function(){logCars(cars);});}

<img src="http://img.blog.csdn.net/20160913233604540?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />