本文实例讲述了node.js实现回调的方法。分享给大家供大家参考，具体如下：
向回调函数传递额外的参数
在调用函数中，使用匿名函数中实现需传递的参数，再次匿名函数内调用回调函数。
var events = require("events");function CarShow() { events.EventEmitter.call(this); this.seeCar = function (make) { this.emit('sawCar', make); }}CarShow.prototype.__proto__ = events.EventEmitter.prototype;var show = new CarShow();function logCar(make) { console.log("Saw a "+make);}function logColorCar(make, color) { console.log("Saw a %s %s ", color, make);}show.on("sawCar", logCar);show.on("sawCar", function (make) { var colors = ["red", "blue", "black", "pink", "green"]; var color = colors[Math.floor(Math.random()*3)]; logColorCar(make, color);});show.seeCar("Ferrari");show.seeCar("Porsche");show.seeCar("Bugatti");在回调中实现闭包
如果某个回调函数需要访问父函数的作用域的变量，就需要使用闭包，在函数块内部封装一个异步调用，并传入所需要的变量。
function logCar(logMsg, callback) { process.nextTick(function () { callback(logMsg); });}var cars = ["猎豹", "捷达", "朗逸"];for(var idx in cars){ var msg = "Saw a "+cars[idx]; logCar(msg, function () { console.log("Normal Callback "+ msg); });}for(var idx in cars){ var msg = "Saw a "+cars[idx]; (function (msg) { logCar(msg, function () { console.log("Closure Callback "+ msg); }) })(msg);}//Normal Callback Saw a 朗逸//Normal Callback Saw a 朗逸//Normal Callback Saw a 朗逸//Closure Callback Saw a 猎豹//Closure Callback Saw a 捷达//Closure Callback Saw a 朗逸链式回调
使用异步函数时，如果两个函数都在事件队列上，则无法保证它们的运行顺序。解决方法是让来自异步函数的回调再次调用该函数，直到没有更多的工作要做，以执行链式回调。
function logCar(car, callback) { console.log("Saw a %$", car); if(cars.length){ process.nextTick(function () { callback(); }); }}function logCars(cars) { var car = cars.pop(); logCar(car, function () { logCars(cars); });}var cars = ["猎豹", "捷达", "朗逸"];logCars(cars);希望本文所述对大家nodejs程序设计有所帮助。
