nodejs基础概念解析

1.什么是回调？

var learn = function(something) {    console.log(something);}var we = function(callback,something){    var something = something + ' is cool';    callback(something);}we(learn,'NodeJs');we(function(something){    console.log(something);},'Jade')

2.什么是同步异步?

var go_home = function(person){    console.log(person+' go home');}var wait_classmate = function(person){    setTimeout(function(){        person += 'wait classmate';        go_home(person);//等到同学在回家    },1000);    go_home(person);//回家以后等同学}wait_classmate('xiao ming');

3.什么是作用域?

var globalVariable = "This is a global variable";   var globalFunction = function(){    console.log('visit globalVariable');    console.log(globalVariable);    var LocalVariable = "This is a local variable";    var localFunction = function(){        console.log('visit LocalVariable');        console.log(LocalVariable);        var innerLocalVariable = "This is a local innerLocalVariable";        var innerLocalFunction = function(){            console.log('visit global/local/innerLocal/Variable');            console.log(globalVariable);            console.log(LocalVariable);            console.log(innerLocalVariable);        }        innerLocalFunction();    }    localFunction();}globalFunction();

4.this上下文对象
this是指向调用该方法的对象

var pet = {    word:"...",    speak:function(){        console.log('speak'+' '+this.word);    }}pet.speak();//this指向petvar pet = function(word){    this.word = word;    this.speak = function(){        console.log('speak'+' '+this.word);    };}var cat = new pet("Miao");cat.speak();cat.word = "Miao Miao MIao ~";cat.speak(); //指向cat对象var dog = new pet("wang wang!");dog.speak();var petSpeak = function(){    console.log(this==window);}petSpeak()；//truevar pet = {    word:"...",    speak:function(){        console.log(this.word);    }}pet.speak();var dog = {    word:"wang wang~"}pet.speak.call(dog,'speak');