一、javascript對象概述

對象中包含一系列屬性,這些屬性時無序的.   每個屬性都有一個字符串key和對應的value.   var obj={x:1,y:2};   obj.x;//1   obj.y;//2      var obj={};   obj[1]=1;   obj["1"]=2;   obj;//object{1:2}      obj[{}]=true;   obj[{x:1}]=true;   obj;//Object{1:2,[object Object]:true}      var obj={};   obj.y=2;   obj.x=1;      function foo(){};   foo.PRototype.z=3;   var obj=new foo();

二、創建對象，原型鏈

1.對象創建-字面量 var obj1={x:1,y:2}; var obj2={  x:1,  y:2,  o:{z:3,n:4} } 2.創建對象-new/原型鏈 function foo(){}//函數對象會默認帶有prototype屬性,改、該屬性為一個對象屬性，該對象也是有原型的，指向Object.prototype,Object.prototype也是有原型的,其值為null foo.prototype.z=3;//為對象添加屬性z=3  var obj=new foo();//創建新對象obj的原型會指向構造器的原型（即foo.prototype） obj.y=2; obj.x=1;  obj.x;//1 obj.y;//2 obj.z;//3 typeof obj.toString();//"function" "z" in obj;//true obj.hasOwnProperty("z");//false //通過原型鏈的方法可以繼承原型鏈上的屬性，同時又不會修改原型鏈上的屬性  3.對象創建-Object.create() var obj=Object.create({x:1});//創建一個對象，并且對象的原型指向{x:1},{x:1}的原型指向Object.prototype,Object.prototype指向null obj.x;//1 typeof obj.toString;//"function" obj.hasOwnProperty("x");//false  并不是所有的對象都含有Object.prototype var obj=Object.create(null);//此時obj的原型直接指向null，不包含Object.prototype,也不會包含Object的toString方法 obj.toString;//undefined 

三、屬性操作

1.屬性讀寫 var obj={x:1,y:2}; obj.x;//1 obj["y"];//2  obj["x"]=3; obj.y=4;  var obj={x1:1,x2:2}; var i=1,n=2; for(;i<=n;i++){  console.log(obj["x"+i]);//1,2 }  var p; for(p in obj){  console.log(obj[p]); } //注意：用for-in遍歷時有可能會把原型鏈上的屬性也遍歷出來，并且其順序不確定 

2.屬性讀寫-異常 var obj={x:1}; obj.y;//undefined var yz=obj.y.z;//TypeError:Cannot read prototype "z" of undefined obj.y.z=2;//TypeError:Cannot set property "z" of undefined  var yz; if(obj.y){  yz=obj.y.z; }  var yz=obj && obj.y && obj.y.z;//三個條件連接起來判斷真假，都為真，則返回最后一個值； 

3.屬性刪除 var person={age:28,title:"fe"}; delete person.age;//true delete person["title"];//true person.age;//undefined delete person.age;//true，重復刪除某個屬性時，仍返回true //注意：刪除屬性時返回true并不表示刪除屬性成功，而是表示該屬性已經不存在了  delete Object.prototype;//false,每個屬性會有一系列標簽來控制它的權限  var descriptor=Object.getOwnPropertyDescriptor(Object,"prototype"); descriptor.configurable;//false,configurable表示是否可配置，其值為false決定了delete Object.prototype的值也為false并且不會生效 

4.屬性檢測 var cat=new Object; cat.legs=4; cat.name="Kitty";  "legs" in cat;//true "abc" in cat;//false "toString" in cat;//true,inherited property!!!  cat.hasOwnProperty("legs");//true cat.hasOwnProperty("toString");//false  cat.propertyIsEnumerable("legs");//true,是否可枚舉 cat.propertyIsEnumerable("toString");//false  自定義一個屬性,并讓它的枚舉標簽為false Object.defineProperty(cat,"price",{enumerable:false,value:1000});//Object.defineProperty中的enumerable默認為false cat.propertyIsEnumerable("price");//false cat.hasOwnProperty("price");//true

5.屬性枚舉 var o={x:1,y:2,z:3}; "toString" in o;//true o.propertyIsEnumerable("toString");//false var key; for(key in o){  console.log(key);//x,y,z }  var obj=Object.create(o); obj.a=4; var key; for(key in obj){  console.log(key);//a,x,y,z }  var obj=Object.create(o); obj.a=4; var key; for(key in obj){  if(obj.hasOwnProperty(key)){   console.log(key);//a  } }

四、get/set方法

例1：

var man={  name:"Bosn",  weibo:"@Bosn",  get age(){   return new Date().getFullYear()-1988;  },  set age(val){   console.log("Age can not be set to "+val);  } } console.log(man.age);//27 man.age=100;//Age can not be set to 100 console.log(man.age);//27 

例2：

var man={  weibo:"@Bosn",  $age:null,  get age(){   if(this.$age==undefined){    return new Date().getFullYear()-1988;   }else{    return this.$age;   }  },  set age(val){   val= +val;//將字符串轉為數字   if(!isNaN(val)&&val>0&&val<150){    this.$age=+val;   }else{    throw new Error("Incorrect val="+val);   }  } } console.log(man.age);//27 man.age=100; console.log(man.age);//100 man.age="abc";//error:Incorrect val=NaN

get/set與原型鏈

function foo(){} Object.defineProperty(foo.prototype,"z",{get:function(){return 1;}});  var obj =new foo();  obj.z;//1 obj.z=10; obj.z;//1 //注意：obj的對象上沒有z屬性并且向上查找時有對于的get或set方法時，當我們嘗試賦值時，實際上會走get或set方法  //通過下面的方法可以為當前對象添加屬性 Object.defineProperty(obj,"z",{value:100,configurable:true}); obj.z;//100 delete obj.z; obj.z;//1

var o={}; Object.defineProperty(o,"x",{value:1});//writable=false,configurable=false var obj=Object.create(o); obj.x;//1 obj.x=200; obj.x;//still 1,can't change it  Object.defineProperty(obj,"x",{writable:true,configurable:true,value:100}); obj.x;//100 obj.x=500; obj.x;//500

五、屬性標簽

通過Object.getOwnPropertyDescriptor("對象","屬性")來查看對象屬性的屬性標簽 例:Object.getOwnPropertyDescriptor({pro:true},"pro");//Object{value:true,writable:true,enumerable:true,configurable:true} Object.getOwnPropertyDescriptor({pro:true},"a");//undefined  管理或設置屬性標簽 Object.defineProperty("對象","屬性","屬性標簽對象") Object.defineProperties("對象","復雜對象") 例1: var person={}; Object.defineProperty(person,"name",{  configurable:false,  writable:false,  enumerable:true,  value:"Bosn Ma" }); person.name;//Bosn Ma person.name=1; person.name;//still Bosn Ma delete person.name;//false Object.defineProperty(person,"type",{  configurable:true,  writable:true,  enumerable:false,  value:"Object" }); Object.keys(person);//["name"],通過Object.keys()可以查看對象的屬性  例2: var person={}; Object.defineProperties(person,{  title:{value:"fe",enumerable:true},  corp:{value"BABA",enumerable:true},  salary:{value:50000,enumberable:true,writable:true} }); Object.getOwnPropertyDescriptor(person,"salary");//Object{value:50000,writable:true,enumerable:true,configurable:false} Object.getOwnPropertyDescriptor(person,"corp");//Object{value:"BABA",writable:false,enumerable:true,configurable:false}  例3:

 var person={}; Object.defineProperties(person,{  title:{value:"fe",enumerable:true},  corp:{value:"BABA",enumerable:true},  salary:{value:50000,enumerable:true,writable:true},  luck:{   get:function(){    return Math.random()>0.5?"good":"bad";   }  },  promote:{   set:function(level){    this.salary*=1+level*0.1;   }  } }); Object.getOwnPropertyDescriptor(person,"salary");//Object{value:50000,writable:true,enumerable:true,configurable:false} Object.getOwnPropertyDescriptor(person,"corp");//Object{value:"BABA",writable:false,enumerable:true,configurable:false} person.salary;//50000 person.promote=2; person.salary;//60000

屬性標簽可以重復被設置：

  var person={}; Object.defineProperty(person,"name",{  value:1111,  configurable:false//configurable為false時，除了writable從true改為false其他屬性修改不允許 }); console.log(person.name); console.log(Object.getOwnPropertyDescriptor(person,"name")); Object.defineProperty(person,"name",{  enumerable:true }); console.log(Object.getOwnPropertyDescriptor(person,"name"));

六、對象標簽

對象標簽主要有3個：[[proto]],[[class]],[[extensible]]

1.原型標簽[[proto]]

2.class標簽，沒有直接的方法來查看class，可以通過Object.prototype.toString來間接地查看

var toSting=Object.prototype.toString; function getType(o){return toSting.call(o).slice(8,-1);};  toSting.call(null);//"[object Null]" getType(null);//"Null" getType(undefined);//"undefined" getType(1);//"Number" getType(new Number(1));//"Number" typeof new Number(1);//"object" getType(true);//"Boolean" getType(new Boolean(true));//"Boolean"

3.extensible標簽表示對象是否可以擴展，屬性是否可以添加

var obj={x:1,y:2}; Object.isExtensible(obj);//true Object.preventExtensions(obj); Object.isExtensible(obj);//false obj.z=1; obj.z;//undefined,add new prototy failed Object.getOwnPropertyDescriptor(obj,"x");//Object{value:1,writable:true,enumerable:true,configurable:true}  Object.seal(obj); Object.getOwnPropertyDescriptor(obj,"x");//Object{value:1,writable:true,enumerable:true,configurable:false} Object.isSealed(obj);//true  Object.freeze(obj); Object.getOwnPropertyDescriptor(obj,"x");//Object{value:1,writable:false,enumerable:true,configurable:false} Object.isFrozen(obj);//true

序列化、其他對象方法

var obj={x:1,y:true,z:[1,2,3],nullVal:null}; JSON.stringify(obj);//"{"x":1,"y":true,"z":[1,2,3],"nullVal":null}"  obj={val:undefined,a:NaN,b:Infinity,c:new Date()}; JSON.stringify(obj);//"{"a":null,"b":null","c":"2015-01-20T14:12:45.910Z"}" //注意：值為undefined時不會被顯示，值為NaN和Infinity時顯示為null,值為時間會被轉為UTU的時間格式  obj=JSON.parse("{"x":1}"); obj.x;//1

序列化-自定義

var obj={  x:1,  y:2,  o:{   o1:1,   o2:2,   toJSON:function(){    return this.o1+this.o2;   }  } }; JSON.stringify(obj);//"{"x:1,"y":2,"o":3}"

其他對象方法

var obj={x:1,y:2}; obj.toString();//"[object Object]" obj.toString=function(){return this.x+this.y}; console.log("Result "+obj);//"Result 3" ,by toString  console.log(+obj);//3,form toString  obj.valueOf=function(){return this.x+this.y+100;}; console.log(+obj);//103,from valueOf  console.log("Result "+obj);//still "Result 103"