概述
對象中包含一系列的屬性，這些屬性無序。每個屬性都有一個key和對應的value。
var obj = {x:1,y:2};
obj.x;//1
obj.y;//2對象的數據類型有：Function、Array、Date ···
對象結構
var obj = {};
obj.y = 2;
obj.x = 1;
function foo(){}
foo.prototype.z = 3;
var obj =new foo();一、對象的創建
第一種方式：字面量
var obj1 = {x : 1, y : 2};
var obj2 = {
x : 1,
y : 2,
o : {
z : 3,
n : 4
}
};第二種方式：new/原型鏈
function foo(){}; //這樣就默認帶有一個foo.prototype對象屬性
foo.prototype.z = 3;
var obj =new foo();
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
obj.z = 5;
obj.hasOwnProperty('z'); // true
foo.prototype.z; // still 3
obj.z; // 5
obj.z = undefined;
obj.z; // undefined
delete obj.z; // true
obj.z; // 3
delete obj.z; // true
obj.z; // still 3!!!第三種方式：Object.create
var obj = Object.create({x : 1});
obj.x // 1
typeof obj.toString // "function"
obj.hasOwnProperty('x');// false
var obj = Object.create(null);
obj.toString // undefined二、屬性的操作
屬性讀寫
var obj = {x : 1, y : 2};
obj.x; // 1
obj["y"]; // 2var obj = {x1 : 1, x2 : 2};
var i = 1, n = 2;
for (; i <= n; i++) {
console.log(obj['x' + i]);
}
// 輸出: 1, 2var p;
for (p in obj) {
console.log(obj[p]);
}
//for-in有可能將原型鏈上面的屬性遍歷下來屬性異常
var obj = {x : 1};
obj.y; // undefined
var yz = obj.y.z; // TypeError: Cannot read property 'z' of undefined
obj.y.z = 2; // TypeError: Cannot set property 'z' of undefined
var 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;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 只是表示不存在這個屬性了，不表示刪除成功
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; // false
function fd() {}
delete fd; // false
//隱式創建的變量可以刪除
ohNo = 1;
window.ohNo; // 1
delete ohNo; // true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
//查看屬性是不是可枚舉的呢？
cat.propertyIsEnumerable('legs'); // true
cat.propertyIsEnumerable('toString'); // false//cat對象的price屬性自己定義是否可枚舉，以下方式不寫默認爲false
Object.defineProperty(cat, 'price', {enumerable : false, value : 1000});
cat.propertyIsEnumerable('price'); // false
cat.hasOwnProperty('price'); // true
if (cat.legs != undefined) {
//不等於表示 !== undefined, or, !== null
}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
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) {
//過濾掉原型鏈上的屬性
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); // 27
man.age = 100; // Age can't be set to 100
console.log(man.age); // still 27接下來將上面的代碼再複雜點：
var man = {
weibo : '@Bosn',
$age : null,
get age() {
if (this.$age == undefined) {
return new Date().getFullYear() - 1988;
} else {
return this.$age;
}
},
set age(val) {
val = +val;//將傳入的字符串轉化爲Number類型（val-0也可以實現）
if (!isNaN(val) && val > 0 && val < 150) {
this.$age = +val;
} else {
throw new Error('Incorrect val = ' + val);
}
}
}get/set遇到原型鏈
function foo() {}
Object.defineProperty(foo.prototype, 'z',
{get : function(){return 1;}});
var obj = new foo();
obj.z; // 1
obj.z = 100;//先前可以在obj中創建屬性爲z值爲100
obj.z; // still 1
Object.defineProperty(obj, 'z',
{value : 100, configurable: true});
obj.z; // 100;
delete obj.z;
obj.z; // back to 1var o = {};
Object.defineProperty(o, 'x', {value : 1}); // writable=false, configurable=false
var obj = Object.create(o);//obj類似於理解爲一個o的指向
obj.x; // 1
obj.x = 200;//writable=false爲不可寫所以賦值無效
obj.x; // still 1, can't change it
//用Object.definProperty();方式來定義屬性，並賦值
Object.defineProperty(obj, 'x', {writable:true, configurable:true, value : 100});
obj.x; // 100
obj.x = 500;
obj.x; // 500三、屬性的權限
Object.getOwnPropertyDescriptor({pro : true}, 'pro');
//{pro : true}是對象，'pro'爲屬性
// Object {value: true, writable: true, enumerable: true, configurable: true}
Object.getOwnPropertyDescriptor({pro : true}, 'a'); // undefined
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; // falseObject.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; // 60000五、對象標籤
proto
class標籤
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標籤
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 property failed
Object.getOwnPropertyDescriptor(obj, 'x');
// Object {value: 1, writable: true, enumerable: true, configurable: true}
Object.seal(obj);//隱藏
Object.getOwnPropertyDescriptor(obj, 'x');
// Object {value: 1, writable: true, enumerable: true, configurable: false}
Object.isSealed(obj); // true
Object.freeze(obj);//凍結
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自定義序列化
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 toString
obj.valueOf = function() {return this.x + this.y + 100;};
+obj; // 103, from valueOf
"Result " + obj; // still "Result 3"