Object

Object class represents one of JavaScript's data types . It is used to store various keyed collections and more complex entities. Objects can be created using the Object() constructor or the object initializer / literal syntax .

描述

Nearly all objects in JavaScript are instances of Object ; a typical object inherits properties (including methods) from Object.prototype , although these properties may be shadowed (a.k.a. overridden). However, an Object may be deliberately created for which this is not true (e.g. by Object.create(null) ), or it may be altered so that this is no longer true (e.g. with Object.setPrototypeOf ).

Changes to the Object prototype object are seen by all objects through prototype chaining, unless the properties and methods subject to those changes are overridden further along the prototype chain. This provides a very powerful although potentially dangerous mechanism to override or extend object behavior.

Object constructor creates an object wrapper for the given value.

  • If the value is null or undefined , it will create and return an empty object.
  • Otherwise, it will return an object of a Type that corresponds to the given value.
  • If the value is an object already, it will return the value.

When called in a non-constructor context, Object behaves identically to new Object() .

另请参阅 object initializer / literal syntax .

Deleting a property from an object

There isn't any method in an Object itself to delete its own properties (such as Map.prototype.delete() ). To do so, one must use the delete operator .

构造函数

Object()
创建新的 Object object. It is a wrapper for the given value.

静态方法

Object.assign()
Copies the values of all enumerable own properties from one or more source objects to a target object.
Object.create()
Creates a new object with the specified prototype object and properties.
Object.defineProperty()
Adds the named property described by a given descriptor to an object.
Object.defineProperties()
Adds the named properties described by the given descriptors to an object.
Object.entries()
Returns an array containing all of the [key, value] pairs of a given object's own enumerable string properties.
Object.freeze()
Freezes an object. Other code cannot delete or change its properties.
Object.fromEntries()
Returns a new object from an iterable of [key, value] pairs. (This is the reverse of Object.entries ).
Object.getOwnPropertyDescriptor()
Returns a property descriptor for a named property on an object.
Object.getOwnPropertyDescriptors()
Returns an object containing all own property descriptors for an object.
Object.getOwnPropertyNames()
Returns an array containing the names of all of the given object's own enumerable and non-enumerable properties.
Object.getOwnPropertySymbols()
Returns an array of all symbol properties found directly upon a given object.
Object.getPrototypeOf()
Returns the prototype (internal [[Prototype]] property) of the specified object.
Object.is()
Compares if two values are the same value. Equates all NaN values (which differs from both Abstract Equality Comparison and Strict Equality Comparison).
Object.isExtensible()
Determines if extending of an object is allowed.
Object.isFrozen()
Determines if an object was frozen.
Object.isSealed()
Determines if an object is sealed.
Object.keys()
Returns an array containing the names of all of the given object's own enumerable string properties.
Object.preventExtensions()
Prevents any extensions of an object.
Object.seal()
Prevents other code from deleting properties of an object.
Object.setPrototypeOf()
Sets the object's prototype (its internal [[Prototype]] property).
Object.values()
Returns an array containing the values that correspond to all of a given object's own enumerable string properties.

实例特性

Object.prototype.constructor
Specifies the function that creates an object's prototype.
Object.prototype.__proto__
Points to the object which was used as prototype when the object was instantiated.
Object.prototype.__noSuchMethod__
Allows a function to be defined that will be executed when an undefined object member is called as a method.

实例方法

Object.prototype.__defineGetter__()
Associates a function with a property that, when accessed, executes that function and returns its return value.
Object.prototype.__defineSetter__()
Associates a function with a property that, when set, executes that function which modifies the property.
Object.prototype.__lookupGetter__()
Returns the function associated with the specified property by the __defineGetter__() 方法。
Object.prototype.__lookupSetter__()
Returns the function associated with the specified property by the __defineSetter__() 方法。
Object.prototype.hasOwnProperty()
Returns a boolean indicating whether an object contains the specified property as a direct property of that object and not inherited through the prototype chain.
Object.prototype.isPrototypeOf()
Returns a boolean indicating whether the object this method is called upon is in the prototype chain of the specified object.
Object.prototype.propertyIsEnumerable()
Returns a boolean indicating if the internal ECMAScript [[Enumerable]] attribute is set.
Object.prototype.toLocaleString()
调用 toString() .
Object.prototype.toString()
Returns a string representation of the object.
Object.prototype.unwatch()
Removes a watchpoint from a property of the object.
Object.prototype.valueOf()
Returns the primitive value of the specified object.
Object.prototype.watch()
Adds a watchpoint to a property of the object.

范例

使用 Object given undefined and null types

The following examples store an empty Object object in o :

let o = new Object()
					
let o = new Object(undefined)
					
let o = new Object(null)
					

使用 Object to create Boolean 对象

The following examples store Boolean objects in o :

// equivalent to o = new Boolean(true)
let o = new Object(true)
					
// equivalent to o = new Boolean(false)
let o = new Object(Boolean())
					

Object prototypes

When altering the behavior of existing Object.prototype methods, consider injecting code by wrapping your extension before or after the existing logic. For example, this (untested) code will pre-conditionally execute custom logic before the built-in logic or someone else's extension is executed.

When a function is called, the arguments to the call are held in the array-like "variable" arguments . For example, in the call myFn(a, b, c) , the arguments within myFn 's body will contain 3 array-like elements corresponding to (a, b, c) .

When modifying prototypes with hooks, pass this and the arguments (the call state) to the current behavior by calling apply() on the function. This pattern can be used for any prototype, such as Node.prototype , Function.prototype , etc.

var current = Object.prototype.valueOf;
// Since my property "-prop-value" is cross-cutting and isn't always
// on the same prototype chain, I want to modify Object.prototype:
Object.prototype.valueOf = function() {
  if (this.hasOwnProperty('-prop-value')) {
    return this['-prop-value'];
  } else {
    // It doesn't look like one of my objects, so let's fall back on
    // the default behavior by reproducing the current behavior as best we can.
    // The apply behaves like "super" in some other languages.
    // Even though valueOf() doesn't take arguments, some other hook may.
    return current.apply(this, arguments);
  }
}
					

Since JavaScript doesn't exactly have sub-class objects, prototype is a useful workaround to make a “base class” object of certain functions that act as objects. For example:

var Person = function(name) {
  this.name = name;
  this.canTalk = true;
};
Person.prototype.greet = function() {
  if (this.canTalk) {
    console.log('Hi, I am ' + this.name);
  }
};
var Employee = function(name, title) {
  Person.call(this, name);
  this.title = title;
};
Employee.prototype = Object.create(Person.prototype);
Employee.prototype.constructor = Employee; //If you don't set Object.prototype.constructor to Employee,
                                           //it will take prototype.constructor of Person (parent).
                                           //To avoid that, we set the prototype.constructor to Employee (child).
Employee.prototype.greet = function() {
  if (this.canTalk) {
    console.log('Hi, I am ' + this.name + ', the ' + this.title);
  }
};
var Customer = function(name) {
  Person.call(this, name);
};
Customer.prototype = Object.create(Person.prototype);
Customer.prototype.constructor = Customer; //If you don't set Object.prototype.constructor to Customer,
                                           //it will take prototype.constructor of Person (parent).
                                           //To avoid that, we set the prototype.constructor to Customer (child).
var Mime = function(name) {
  Person.call(this, name);
  this.canTalk = false;
};
Mime.prototype = Object.create(Person.prototype);
Mime.prototype.constructor = Mime; //If you don't set Object.prototype.constructor to Mime,
                                   //it will take prototype.constructor of Person (parent).
                                   //To avoid that, we set the prototype.constructor to Mime (child).
var bob = new Employee('Bob', 'Builder');
var joe = new Customer('Joe');
var rg = new Employee('Red Green', 'Handyman');
var mike = new Customer('Mike');
var mime = new Mime('Mime');
bob.greet();
// Hi, I am Bob, the Builder
joe.greet();
// Hi, I am Joe
rg.greet();
// Hi, I am Red Green, the Handyman
mike.greet();
// Hi, I am Mike
mime.greet();
					

规范

规范
ECMAScript (ECMA-262)
The definition of 'Object' in that specification.

浏览器兼容性

更新 GitHub 上的兼容性数据
Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet Node.js
Object Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
Object() 构造函数 Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
assign Chrome 45 Edge 12 Firefox 34 IE No Opera 32 Safari 9 WebView Android 45 Chrome Android 45 Firefox Android 34 Opera Android 32 Safari iOS 9 Samsung Internet Android 5.0 nodejs 4.0.0
构造函数 Chrome 1 Edge 12 Firefox 1 IE 4 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
create Chrome 5 Edge 12 Firefox 4 IE 9 Opera 11.6 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 5 Samsung Internet Android 1.0 nodejs Yes
__defineGetter__
弃用
Chrome 1 Edge 12 Firefox 1
1
Starting with Firefox 48, this method can no longer be called at the global scope without any object. A TypeError will be thrown otherwise. Previously, the global object was used in these cases automatically, but this is no longer the case.
IE 11 Opera 9.5 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
defineProperties Chrome 5 Edge 12 Firefox 4 IE 9 Opera 11.6 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 5 Samsung Internet Android 1.0 nodejs Yes
defineProperty Chrome 5 Edge 12 Firefox 4 IE 9
9
部分支持 8
In Internet Explorer 8, this was only supported on DOM objects and with some non-standard behaviors. This was later fixed in Internet Explorer 9.
Opera 11.6 Safari 5.1
5.1
Also supported in Safari 5, but not on DOM objects.
WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 6
6
Also supported in Safari for iOS 4.2, but not on DOM objects.
Samsung Internet Android 1.0 nodejs Yes
__defineSetter__
弃用
Chrome 1 Edge 12 Firefox 1
1
Starting with Firefox 48, this method can no longer be called at the global scope without any object. A TypeError will be thrown otherwise. Previously, the global object was used in these cases automatically, but this is no longer the case.
IE 11 Opera 9.5 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
entries Chrome 54 Edge 14 Firefox 47 IE No Opera 41 Safari 10.1 WebView Android 54 Chrome Android 54 Firefox Android 47 Opera Android 41 Safari iOS 10.3 Samsung Internet Android 6.0 nodejs 7.0.0
7.0.0
6.5.0
Disabled
Disabled From version 6.5.0: this feature is behind the --harmony runtime flag.
freeze Chrome 6 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5.1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 6 Samsung Internet Android 1.0 nodejs Yes
fromEntries Chrome 73 Edge 79 Firefox 63 IE No Opera 60 Safari 12.1 WebView Android 73 Chrome Android 73 Firefox Android 63 Opera Android No Safari iOS 12.2 Samsung Internet Android No nodejs 12.0.0
getOwnPropertyDescriptor Chrome 5 Edge 12 Firefox 4 IE 9
9
部分支持 8
In Internet Explorer 8, this was only supported on DOM objects and with some non-standard behaviors. This was later fixed in Internet Explorer 9.
Opera 12 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 5 Samsung Internet Android 1.0 nodejs Yes
getOwnPropertyDescriptors Chrome 54 Edge 15 Firefox 50 IE No Opera 41 Safari 10 WebView Android 54 Chrome Android 54 Firefox Android 50 Opera Android 41 Safari iOS 10 Samsung Internet Android 6.0 nodejs 7.0.0
7.0.0
6.5.0
Disabled
Disabled From version 6.5.0: this feature is behind the --harmony runtime flag.
getOwnPropertyNames Chrome 5 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 5 Samsung Internet Android 1.0 nodejs Yes
getOwnPropertySymbols Chrome 38 Edge 12 Firefox 36 IE No Opera 25 Safari 9 WebView Android 38 Chrome Android 38 Firefox Android 36 Opera Android 25 Safari iOS 9 Samsung Internet Android 3.0 nodejs 0.12
getPrototypeOf Chrome 5 Edge 12 Firefox 3.5 IE 9 Opera 12.1 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12.1 Safari iOS 5 Samsung Internet Android 1.0 nodejs Yes
hasOwnProperty Chrome 1 Edge 12 Firefox 1 IE 5.5 Opera 5 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
is Chrome 30 Edge 12 Firefox 22 IE No Opera 17 Safari 9 WebView Android ≤37 Chrome Android 30 Firefox Android 22 Opera Android 18 Safari iOS 9 Samsung Internet Android 2.0 nodejs 0.10
isExtensible Chrome 6 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5.1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 6 Samsung Internet Android 1.0 nodejs Yes
isFrozen Chrome 6 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5.1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 6 Samsung Internet Android 1.0 nodejs Yes
isPrototypeOf Chrome 1 Edge 12 Firefox 1 IE 9 Opera 4 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
isSealed Chrome 6 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5.1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 6 Samsung Internet Android 1.0 nodejs Yes
keys Chrome 5 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 5 Samsung Internet Android 1.0 nodejs Yes
__lookupGetter__
弃用
Chrome 1 Edge 12 Firefox 1 IE 11 Opera 9.5 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
__lookupSetter__
弃用
Chrome 1 Edge 12 Firefox 1 IE 11 Opera 9.5 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
preventExtensions Chrome 6 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5.1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 6 Samsung Internet Android 1.0 nodejs Yes
propertyIsEnumerable Chrome 1 Edge 12 Firefox 1 IE 5.5 Opera 4 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
__proto__
弃用
Chrome 1 Edge 12 Firefox 1 IE 11 Opera 10.5 Safari 3 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 11 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
seal Chrome 6 Edge 12 Firefox 4 IE 9 Opera 12 Safari 5.1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 12 Safari iOS 6 Samsung Internet Android 1.0 nodejs Yes
setPrototypeOf Chrome 34 Edge 12 Firefox 31 IE 11 Opera 21 Safari 9 WebView Android 37 Chrome Android 34 Firefox Android 31 Opera Android 21 Safari iOS 9 Samsung Internet Android 2.0 nodejs 0.12
toLocaleString Chrome 1 Edge 12 Firefox 1 IE 5.5 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
toSource
弃用 非标
Chrome No Edge No Firefox 1 — 74
1 — 74
Starting in Firefox 74, toSource() is no longer available for use by web content. It is still allowed for internal and privileged code.
IE No Opera No Safari No WebView Android No Chrome Android No Firefox Android 4 Opera Android No Safari iOS No Samsung Internet Android No nodejs No
toString() Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
valueOf Chrome 1 Edge 12 Firefox 1 IE 4 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs Yes
values Chrome 54 Edge 14 Firefox 47 IE No Opera 41 Safari 10.1 WebView Android 54 Chrome Android 54 Firefox Android 47 Opera Android 41 Safari iOS 10.3 Samsung Internet Android 6.0 nodejs 7.0.0
7.0.0
6.5.0
Disabled
Disabled From version 6.5.0: this feature is behind the --harmony runtime flag.

图例

完整支持
完整支持
不支持
不支持
非标。预期跨浏览器支持较差。
弃用。不要用于新网站。
弃用。不要用于新网站。
见实现注意事项。
用户必须明确启用此特征。
用户必须明确启用此特征。

另请参阅

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