在此页

• 句法
• 描述
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

Object.isExtensible() method determines if an object is extensible (whether it can have new properties added to it).

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

句法

Object.isExtensible(obj)
					

参数

obj

The object which should be checked.

返回值

A 布尔 indicating whether or not the given object is extensible.

描述

Objects are extensible by default: they can have new properties added to them, and (in engines that support __proto__ ) their __proto__ property can be modified. An object can be marked as non-extensible using Object.preventExtensions() , Object.seal() ，或 Object.freeze() .

范例

Using Object.isExtensible

// 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
					

Non-object coercion

In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError . In ES2015, a non-object argument will be treated as if it was a non-extensible ordinary object, simply return false .

Object.isExtensible(1);
// TypeError: 1 is not an object (ES5 code)
Object.isExtensible(1);
// false                         (ES2015 code)
					

规范

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

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 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
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

图例

完整支持

完整支持

另请参阅

• Object.preventExtensions()
• Object.seal()
• Object.isSealed()
• Object.freeze()
• Object.isFrozen()
• Reflect.isExtensible()

元数据

• 最后修改： May 25, 2020

相关话题

1. 标准内置对象
2. Object
3. 特性
   1. Object.prototype.__proto__
   2. Object.prototype.constructor
4. 方法
   1. Object.assign()
   2. Object.create()
   3. Object.defineProperties()
   4. Object.defineProperty()
   5. Object.entries()
   6. Object.freeze()
   7. Object.fromEntries()
   8. Object.getOwnPropertyDescriptor()
   9. Object.getOwnPropertyDescriptors()
   10. Object.getOwnPropertyNames()
   11. Object.getOwnPropertySymbols()
   12. Object.getPrototypeOf()
   13. Object.is()
   14. Object.isExtensible()
   15. Object.isFrozen()
   16. Object.isSealed()
   17. Object.keys()
   18. Object.preventExtensions()
   19. Object.prototype.__defineGetter__()
   20. Object.prototype.__defineSetter__()
   21. Object.prototype.__lookupGetter__()
   22. Object.prototype.__lookupSetter__()
   23. Object.prototype.hasOwnProperty()
   24. Object.prototype.isPrototypeOf()
   25. Object.prototype.propertyIsEnumerable()
   26. Object.prototype.toLocaleString()
   27. Object.prototype.toSource()
   28. Object.prototype.toString()
   29. Object.prototype.valueOf()
   30. Object.seal()
   31. Object.setPrototypeOf()
   32. Object.values()
5. 继承：
6. Function
7. 特性
   1. Function.arguments
   2. Function.caller
   3. Function.displayName
   4. Function.length
   5. Function.name
8. 方法
   1. Function.prototype.apply()
   2. Function.prototype.bind()
   3. Function.prototype.call()
   4. Function.prototype.toSource()
   5. Function.prototype.toString()