作用域
调用函数访问变量的能力
//全局变量var globalVariable = ‘This is global variable‘//全局函数function globalFunction(){ ???//局部变量 ???var localVariable = ?‘This is local variable‘ ???console.log(‘visit gloabl/local variable‘) ???console.log(globalVariable) ???console.log(localVariable) ???globalVariable = ‘this is change variable‘ ???console.log(globalVariable) ???//局部函数 ???function loaclFunction(){ ???????//局部变量 ???????var innerLocalVariable = ‘this is inner local variable‘ ???????console.log(‘visit gloabl/local/innerLocal variable‘) ???????console.log(globalVariable) ???????console.log(localVariable) ???????console.log(innerLocalVariable) ???} ???//作用域内可访问局部函数 ???loaclFunction()}//在全局不能访问局部变量和函数globalFunction()上下文
和this关键字有关，是调用当前可执行代码的对象的引用
this指向函数拥有者，只能在函数中使用
this指向构造函数
var pet = { ???words:‘..‘, ???speak:function(){ ???????console.log(this.words) ???????console.log(this==pet) ???}}pet.speak()this指向全局对象
function pet(words){ ???this.words = words ???console.log(this.words) ???console.log(this==global)}//this指向了全局global对象pet(‘..‘)this指向实例对象
function Pet(words){ ???this.words = words ???this.speak = function(){ ???????console.log(this.words) ???????console.log(this) ???}}var cat = new Pet(‘Miao‘)cat.speak();使用call和apply改变上下文引用对象
this指向引用方法的对象
var pet = { ???words:‘..‘, ???speak:function(say){ ???????console.log(say + ‘ ‘ + this.words) ???}}pet.speak(‘haha‘)使用call-apply
var pet = { ???words:‘..‘, ???speak:function(say,free){ ???????console.log(say + ‘ ‘ + free+ ‘ ‘+ this.words) ???}}var dog={ ???words:‘wawa‘}pet.speak.call(dog,‘haha‘,‘lala‘)pet.speak.apply(dog,[‘haha‘,‘lala‘])使用call和apply方便实现继承
function Pet(words){ ???this.words = words ???this.speak = function(){ ???????console.log(this.words) ???}}//Dog继承Pet,拥有了Pet的speak方法function Dog(words){ ???Pet.call(this,words)}var dog = new Dog(‘wawa‘)dog.speak()06慕课网《进击Node.js基础（一）》作用域和上下文
原文地址：https://www.cnblogs.com/-beauTiFul/p/9095696.html