js - object的属性操作

视频学习地址：

http://www.imooc.com/video/6002

原文PPT下载地址：

http://img.mukewang.com/down/54c5ec1a000141f100000000.zip

1、属性删除

var person = {age : 28, title : 'fe'};
delete person.age; // true
delete person['title']; // true
person.age; // undefined
delete person.age; // true

delete Object.prototype; // false,

var descriptor = Object.getOwnPropertyDescriptor(Object, 'prototype');
descriptor.configurable; // false

2、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'); // true
cat.hasOwnProperty('toString'); // false

cat.propertyIsEnumerable('legs'); // true
cat.propertyIsEnumerable('toString'); // false

if (cat && cat.legs) {
    cat.legs *= 2;
}

if (cat.legs != undefined) {
    // !== undefined, or, !== null
}

if (cat.legs !== undefined) {
    // only if cat.legs is not undefined
}

3、属性枚举

var o = {x : 1, y : 2, z : 3};
'toString' in o; // true
o.propertyIsEnumerable('toString'); // false  说明原型链上Object.prototype中的toString()方法不可枚举
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  只枚举自身的属性
    }
}

5、属性的getter / setter 

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); //
man.age = 100; // Age can't be set to 100
console.log(man.age); // still 27

---

var man = {
    weibo : '@Bosn',
    $age : null,
    get age() {
        if (this.$age == undefined) {
            return new Date().getFullYear() - 1988;
        } else {
            return this.$age;
        }
    },
    set age(val) {
        val = +val;
        if (!isNaN(val) && val > 0 && val < 150) {
            this.$age = +val;
        } else {
            throw new Error('Incorrect val = ' + val);
        }
    }
}

console.log(man.age); //
man.age = 100;
console.log(man.age); // 100;
man.age = 'abc'; // error:Incorrect val = NaN

6、getter / setter 和 defineProperty

function foo() {}

Object.defineProperty(foo.prototype, 'z',
    {get : function(){return 1;}});

var obj = new foo();

obj.z; //
obj.z = 10;
obj.z; // still 1

Object.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=false
var obj = Object.create(o);
obj.x; //
obj.x = 200;
obj.x; // still 1, can't change it

Object.defineProperty(obj, 'x', {writable:true, configurable:true, value : 100});
obj.x; //
obj.x = 500;
obj.x; //

7、属性的权限设置 Object.defineProperty

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.defineProperties(person, {
    title : {value : 'fe', enumerable : true},
    corp : {value : 'BABA', enumerable : true},
    salary : {value : 50000, enumerable : 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}

---

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