js深入理解（二）

1.函数闭包

var scope = "global scope";function checkScope (){   var scope = "local scope";  function f(){return scope;}   return f;}//checkScope ()()输出local scopevar scope = "global scope";function checkScope (){    var scope = "local scope";    function f(){        return scope;    }    return f();}//checkScope()输出local scope

2.with语句 ，将对象属性作用域链添加至顶层（在严格模式中不可用）

function Lakers() {       this.name = "kobe bryant";       this.age = "28";       this.gender = "boy";}var people=new Lakers();with(people){       var str = "姓名: " + name + "<br>";       str += "年龄：" + age + "<br>";       str += "性别：" + gender;}  (function (){    alert(str);}()); //输出 姓名: kobe bryant<br>年龄：28<br>性别：boy

3.为js添加断点

function ddd(o){if (o==undefined) {debugger;};}

4.对象引用,引用值改变，原对象值也跟着变。

function a(){ //use constructorthis.user="user";this.pwd="pwd";this.get="get";return this;}  var c = a();(function (){alert(c.user);var b = c;b.user = "ddd";alert(c.user);}());//输出：user  ddd

5.创建对象的几种方式。

//通过构造函数创建 var obj = new ddd("a1","a2"); function ddd (a1,a2,){     this.a1=a1;     this.a2=a2; }//对象直接量 var obj =  {a1:"ddd",a2:"ccc"}; //通过继承来创建 var a = {x:1,y:2}; var obj = Object.create(a);//obj继承了a

6.获取对象可枚举属性

//获取对象属性名称,返回数组Object.getOwnPropertyNames(obj);//获取对象属性，返回数组Object.keys(obj);

7.对象存取器属性

var o = {$n:0,//$暗示私有属性get getN(){return this.$n;},set setN(n){this.$n=n;}} ;(function (){o.setN=4;alert(o.getN);}());//输出 4

8.获取对象属性特性

//是否可读Object.getOwnPropertyDescriptor({x:1},"x").writable//获取属性值Object.getOwnPropertyDescriptor({x:1},"x").value//是否可枚举Object.getOwnPropertyDescriptor({x:1},"x").enumerable//是否可配置，该property的属性是否可以修改，property是否可以删除。Object.getOwnPropertyDescriptor({x:1},"x").configurable

9.定义属性特性，不能定义继承的属性

var a = {x:1};Object.defineProperty(a,"x",{value:4,writable:false,configurable:true,enumerable:true});a.x = 3;alert(a.x);//输出 4//定义多个属性特性(function (){    var a = {x:1,y:2,$n:0,get getN(){return this.$n;}};    Object.defineProperties(a,{x:{value:4,writable:false,configurable:true,enumerable:true},                               y:{value:4,writable:false,configurable:true,enumerable:true},                               getN:{get:function(){return this.$n+2;},configurable:true,enumerable:true}});    a.y = 3;    alert(a.getN);/输出 2}());