Object.isExtensible

Object.isExtensible()方法判断一个对象是否是可扩展的（是否可以在它上面添加新的属性）。

语法

Object.isExtensible(obj)

参数

obj需要检测的对象

返回值

Boolean表示给定对象是否可扩展。

描述

默认情况下，对象是可扩展的：即可以为他们添加新的属性。以及它们的 __proto__ 属性可以被更改。Object.preventExtensions，Object.seal 或 Object.freeze 方法都可以标记一个对象为不可扩展（non-extensible）。

示例

// New objects are extensible.
var empty = {};
Object.isExtensible(empty); // === true

// ...but that can be changed.
Object.preventExtensions(empty);
Object.isExtensible(empty); // === false

// Sealed objects are by definition non-extensible.
var sealed = Object.seal({});
Object.isExtensible(sealed); // === false

// Frozen objects are also by definition non-extensible.
var frozen = Object.freeze({});
Object.isExtensible(frozen); // === false

注意事项

在 ES5 中，如果参数不是一个对象类型，将抛出一个 TypeError 异常。在 ES6 中， non-object 参数将被视为一个不可扩展的普通对象，因此会返回 false 。

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

Object.isExtensible(1);
// false                         (ES2015 code)

规范

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

浏览器兼容性

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.preventExtensions()

• Object.seal()

• Object.isSealed()

• Object.freeze()

• Object.isFrozen()

• Reflect.isExtensible()

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