本文實(shí)例講述了node.js實(shí)現(xiàn)回調(diào)的方法。分享給大家供大家參考，具體如下：
向回調(diào)函數(shù)傳遞額外的參數(shù)
在調(diào)用函數(shù)中，使用匿名函數(shù)中實(shí)現(xiàn)需傳遞的參數(shù)，再次匿名函數(shù)內(nèi)調(diào)用回調(diào)函數(shù)。
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");在回調(diào)中實(shí)現(xiàn)閉包
如果某個(gè)回調(diào)函數(shù)需要訪問(wèn)父函數(shù)的作用域的變量，就需要使用閉包，在函數(shù)塊內(nèi)部封裝一個(gè)異步調(diào)用，并傳入所需要的變量。
function logCar(logMsg, callback) { process.nextTick(function () { callback(logMsg); });}var cars = ["獵豹", "捷達(dá)", "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 獵豹//Closure Callback Saw a 捷達(dá)//Closure Callback Saw a 朗逸鏈?zhǔn)交卣{(diào)
使用異步函數(shù)時(shí)，如果兩個(gè)函數(shù)都在事件隊(duì)列上，則無(wú)法保證它們的運(yùn)行順序。解決方法是讓來(lái)自異步函數(shù)的回調(diào)再次調(diào)用該函數(shù)，直到?jīng)]有更多的工作要做，以執(zhí)行鏈?zhǔn)交卣{(diào)。
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 = ["獵豹", "捷達(dá)", "朗逸"];logCars(cars);希望本文所述對(duì)大家nodejs程序設(shè)計(jì)有所幫助。
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