对象理解原型链

概述

对象中包含一系列的属性，这些属性无序。每个属性都有一个key和对应的value。

var obj = {x:1,y:2};obj.x;//1obj.y;//2

对象的数据类型有：Function、Array、Date ···

对象结构

var obj = {};obj.y = 2;obj.x = 1;function foo(){}foo.prototype.z = 3;var obj =new foo();

一、对象的创建

第一种方式：字面量

var obj1 = {x : 1, y : 2};var obj2 = {    x : 1,    y : 2,    o : {        z : 3,        n : 4    }};

第二种方式：new/原型链

function foo(){};   //这样就默认带有一个foo.prototype对象属性foo.prototype.z = 3;var obj =new foo();obj.y = 2;obj.x = 1;obj.x; // 1obj.y; // 2obj.z; // 3typeof obj.toString; // 'function''z' in obj; // trueobj.hasOwnProperty('z'); // falseobj.z = 5;obj.hasOwnProperty('z'); // truefoo.prototype.z; // still 3obj.z; // 5obj.z = undefined;obj.z; // undefineddelete obj.z; // trueobj.z; // 3delete obj.z; // trueobj.z; // still 3!!!

第三种方式：Object.create

var obj = Object.create({x : 1});obj.x // 1typeof obj.toString // "function"obj.hasOwnProperty('x');// false

var obj = Object.create(null);obj.toString // undefined

二、属性的操作

属性读写

var obj = {x : 1, y : 2};obj.x; // 1obj["y"]; // 2

var obj = {x1 : 1, x2 : 2};var i = 1, n = 2;for (; i <= n; i++) {    console.log(obj['x' + i]);}// 输出: 1, 2

var p;for (p in obj) {    console.log(obj[p]);}//for-in有可能将原型链上面的属性遍历下来

属性异常

var obj = {x : 1};obj.y; // undefinedvar yz = obj.y.z; // TypeError: Cannot read property 'z' of undefinedobj.y.z = 2; // TypeError: Cannot set property 'z' of undefinedvar yz;if (obj && obj.y && obj.y.z) {    yz = obj.y.z;}//或者如下巧用操作符var yz = obj && obj.y && obj.y.z;

属性删除

var person = {age : 28, title : 'fe'};delete person.age; // truedelete person['title']; // trueperson.age; // undefineddelete person.age; // true  只是表示不存在这个属性了，不表示删除成功delete Object.prototype; // false,var descriptor = Object.getOwnPropertyDescriptor(Object, 'prototype');descriptor.configurable; // false   是否可配置，false表示不可配置

var globalVal = 1;delete globalVal; // falsefunction fd() {}delete fd; // false//隐式创建的变量可以删除ohNo = 1;window.ohNo; // 1delete ohNo; // true

属性检测

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'); // truecat.hasOwnProperty('toString'); // false//查看属性是不是可枚举的呢？cat.propertyIsEnumerable('legs'); // truecat.propertyIsEnumerable('toString'); // false

//cat对象的price属性自己定义是否可枚举，以下方式不写默认为falseObject.defineProperty(cat, 'price', {enumerable : false, value : 1000});cat.propertyIsEnumerable('price'); // falsecat.hasOwnProperty('price'); // trueif (cat.legs != undefined) {    //不等于表示 !== undefined, or, !== null}

属性枚举

var o = {x : 1, y : 2, z : 3};'toString' in o; // trueo.propertyIsEnumerable('toString'); // falsevar key;for (key in o) {    console.log(key); // x, y, z    console.log(o.key);//1,2,3    console.log(0[key]);//1,2,3}

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) {    //过滤掉原型链上的属性    if (obj.hasOwnProperty(key)) {        console.log(key); // a    }}

getter/setter方法

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

接下来将上面的代码再复杂点：

var man = {    weibo : '@Bosn',    $age : null,    get age() {        if (this.$age == undefined) {            return new Date().getFullYear() - 1988;        } else {            return this.$age;        }    },    set age(val) {        val = +val;//将传入的字符串转化为Number类型（val-0也可以实现）        if (!isNaN(val) && val > 0 && val < 150) {            this.$age = +val;        } else {            throw new Error('Incorrect val = ' + val);        }    }}

get/set遇到原型链

function foo() {}Object.defineProperty(foo.prototype, 'z',     {get : function(){return 1;}});var obj = new foo();obj.z; // 1obj.z = 100;//先前可以在obj中创建属性为z值为100obj.z; // still 1Object.defineProperty(obj, 'z', {value : 100, configurable: true});obj.z; // 100;delete obj.z;obj.z; // back to 1

var o = {};Object.defineProperty(o, 'x', {value : 1}); // writable=false, configurable=falsevar obj = Object.create(o);//obj类似于理解为一个o的指向obj.x; // 1obj.x = 200;//writable=false为不可写所以赋值无效obj.x; // still 1, can't change it//用Object.definProperty();方式来定义属性，并赋值Object.defineProperty(obj, 'x', {writable:true, configurable:true, value : 100});obj.x; // 100obj.x = 500;obj.x; // 500

三、属性的权限

Object.getOwnPropertyDescriptor({pro : true}, 'pro');//{pro : true}是对象，'pro'为属性// Object {value: true, writable: true, enumerable: true, configurable: true}Object.getOwnPropertyDescriptor({pro : true}, 'a'); // undefinedvar person = {};Object.defineProperty(person, 'name', {    configurable : false,    writable : false,    enumerable : true,    value : "Bosn Ma"});person.name; // Bosn Maperson.name = 1;person.name; // still Bosn Madelete person.name; // false

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; // 50000person.promote = 2;person.salary; // 60000

五、对象标签

proto

class标签

var toString = Object.prototype.toString;function getType(o){return toString.call(o).slice(8,-1);};toString.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"

extensible标签

var obj = {x : 1, y : 2};Object.isExtensible(obj); // trueObject.preventExtensions(obj);Object.isExtensible(obj); // falseobj.z = 1;obj.z; // undefined, add new property failedObject.getOwnPropertyDescriptor(obj, 'x');// Object {value: 1, writable: true, enumerable: true, configurable: true}Object.seal(obj);//隐藏Object.getOwnPropertyDescriptor(obj, 'x');// Object {value: 1, writable: true, enumerable: true, configurable: false}Object.isSealed(obj); // trueObject.freeze(obj);//冻结Object.getOwnPropertyDescriptor(obj, 'x');// Object {value: 1, writable: false, enumerable: true, configurable: false}Object.isFrozen(obj); // true// [caution] not affects prototype chain!!!

序列化

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":"2015-01-20T14:15:43.910Z"}"obj = JSON.parse('{"x" : 1}');obj.x; // 1

自定义序列化

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}"

其他方法

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