JavaScript ES5 对象

ECMAScript 5 (2009) 向 JavaScript 添加了许多新的对象方法。

管理对象

// Create object with an existing object as prototype
Object.create()

// Adding or changing an object property
Object.defineProperty(object, property, descriptor)

// Adding or changing object properties
Object.defineProperties(object, descriptors)

// Accessing Properties
Object.getOwnPropertyDescriptor(object, property)

// Returns all properties as an array
Object.getOwnPropertyNames(object)

// Accessing the prototype
Object.getPrototypeOf(object)

// Returns enumerable properties as an array
Object.keys(object)

保护物体

// Prevents adding properties to an object
Object.preventExtensions(object)

// Returns true if properties can be added to an object
Object.isExtensible(object)

// Prevents changes of object properties (not values)
Object.seal(object)

// Returns true if object is sealed
Object.isSealed(object)

// Prevents any changes to an object
Object.freeze(object)

// Returns true if object is frozen
Object.isFrozen(object)

更改属性值

语法

Object.defineProperty(object, property, {value : value})

此示例更改属性值：

示例

const person = {
firstName: "John",
lastName : "Doe",
language : "EN"
};

// Change a property
Object.defineProperty(person, "language", {value : "NO"});

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更改元数据

ES5 允许更改以下属性元数据：

writable : true // Property value can be changed
enumerable : true // Property can be enumerated
configurable : true // Property can be reconfigured

writable : false // Property value can not be changed
enumerable : false // Property can be not enumerated
configurable : false // Property can be not reconfigured

ES5 允许更改 getter 和 setter：

// Defining a getter
get: function() { return language }
// Defining a setter
set: function(value) { language = value }

此示例使语言变为只读：

Object.defineProperty(person, "language", {writable:false});

此示例使语言不可枚举：

Object.defineProperty(person, "language", {enumerable:false});

列出所有属性

此示例列出了对象的所有属性：

示例

const person = {
firstName: "John",
lastName : "Doe",
language : "EN"
};

Object.defineProperty(person, "language", {enumerable:false});
Object.getOwnPropertyNames(person); // Returns an array of properties

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列出可枚举属性

此示例仅列出对象的可枚举属性：

示例

const person = {
firstName: "John",
lastName : "Doe",
language : "EN"
};

Object.defineProperty(person, "language", {enumerable:false});
Object.keys(person); // Returns an array of enumerable properties

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添加属性

此示例向对象添加一个新属性：

示例

// Create an object:
const person = {
firstName: "John",
lastName : "Doe",
language : "EN"
};

// Add a property
Object.defineProperty(person, "year", {value:"2008"});

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添加 Getter 和 Setter

这个Object.defineProperty()方法也可用于添加 Getters 和 Setters：

示例

//Create an object
const person = {firstName:"John", lastName:"Doe"};

// Define a getter
Object.defineProperty(person, "fullName", {
get: function () {return this.firstName + " " + this.lastName;}
});

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反例

示例

// Define object
const obj = {counter:0};

// Define setters
Object.defineProperty(obj, "reset", {
  get : function () {this.counter = 0;}
});
Object.defineProperty(obj, "increment", {
  get : function () {this.counter++;}
});
Object.defineProperty(obj, "decrement", {
  get : function () {this.counter--;}
});
Object.defineProperty(obj, "add", {
  set : function (value) {this.counter += value;}
});
Object.defineProperty(obj, "subtract", {
  set : function (i) {this.counter -= i;}
});

// Play with the counter:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;

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