Object.isFrozen

Object.isFrozen()方法判断一个对象是否被冻结。

语法

Object.isFrozen(obj)

参数

obj被检测的对象。

返回值

表示给定对象是否被冻结的Boolean。

描述

一个对象是冻结的是指它不可扩展，所有属性都是不可配置的，且所有数据属性（即没有getter或setter组件的访问器的属性）都是不可写的。

例子

// A new object is extensible, so it is not frozen.
Object.isFrozen({}); // === false

// An empty object which is not extensible
// is vacuously frozen.
var vacuouslyFrozen = Object.preventExtensions({});
Object.isFrozen(vacuouslyFrozen); // === true

// A new object with one property is also extensible,
// ergo not frozen.
var oneProp = { p: 42 };
Object.isFrozen(oneProp); // === false

// Preventing extensions to the object still doesn't 
// make it frozen, because the property is still 
// configurable (and writable).
Object.preventExtensions(oneProp);
Object.isFrozen(oneProp); // === false

// ...but then deleting that property makes the object
// vacuously frozen.
delete oneProp.p;
Object.isFrozen(oneProp); // === true

// A non-extensible object with a non-writable
// but still configurable property is not frozen.
var nonWritable = { e: 'plep' };
Object.preventExtensions(nonWritable);
Object.defineProperty(nonWritable, 'e', {
  writable: false
}); // make non-writable
Object.isFrozen(nonWritable); // === false

// Changing that property to non-configurable
// then makes the object frozen.
Object.defineProperty(nonWritable, 'e', {
  configurable: false
}); // make non-configurable
Object.isFrozen(nonWritable); // === true

// A non-extensible object with a non-configurable
// but still writable property also isn't frozen.
var nonConfigurable = { release: 'the kraken!' };
Object.preventExtensions(nonConfigurable);
Object.defineProperty(nonConfigurable, 'release', {
  configurable: false
});
Object.isFrozen(nonConfigurable); // === false

// Changing that property to non-writable
// then makes the object frozen.
Object.defineProperty(nonConfigurable, 'release', {
  writable: false
});
Object.isFrozen(nonConfigurable); // === true

// A non-extensible object with a configurable
// accessor property isn't frozen.
var accessor = { get food() { return 'yum'; } };
Object.preventExtensions(accessor);
Object.isFrozen(accessor); // === false

// ...but make that property non-configurable
// and it becomes frozen.
Object.defineProperty(accessor, 'food', {
  configurable: false
});
Object.isFrozen(accessor); // === true

// But the easiest way for an object to be frozen
// is if Object.freeze has been called on it.
var frozen = { 1: 81 };
Object.isFrozen(frozen); // === false
Object.freeze(frozen);
Object.isFrozen(frozen); // === true

// By definition, a frozen object is non-extensible.
Object.isExtensible(frozen); // === false

// Also by definition, a frozen object is sealed.
Object.isSealed(frozen); // === true

注意

在 ES5 中，如果参数不是一个对象类型，将抛出一个TypeError异常。在 ES2015 中，非对象参数将被视为一个冻结的普通对象，因此会返回true。

Object.isFrozen(1);
// TypeError: 1 is not an object (ES5 code)

Object.isFrozen(1);
// true                          (ES2015 code)

规范

Specification	Status	Comment
ECMAScript 5.1 (ECMA-262)The definition of 'Object.isFrozen' in that specification.	Standard	Initial definition. Implemented in JavaScript 1.8.5.
ECMAScript 2015 (6th Edition, ECMA-262)The definition of 'Object.isFrozen' in that specification.	Standard	​
ECMAScript Latest Draft (ECMA-262)The definition of 'Object.isFrozen' in that specification.	Living Standard	​

浏览器兼容

Feature	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic Support	6	(Yes)	4	9	12	5.1

Feature	Android	Chrome for Android	Edge mobile	Firefox for Android	IE mobile	Opera Android	iOS Safari
Basic Support	(Yes)	(Yes)	(Yes)	(Yes)	(Yes)	(Yes)	(Yes)

See also

• Object.freeze()

• Object.preventExtensions()

• Object.isExtensible()

• Object.seal()

• Object.isSealed()

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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/isFrozen