Object.isExtensible()

¥Syntax

Object.isExtensible(obj)

¥Parameters

obj

应检查的对象。

¥Return value

Boolean 指示给定对象是否可扩展。

¥A Boolean indicating whether or not the given object is extensible.

¥Description

对象默认是可扩展的：它们可以添加新属性，并且可以重新分配它们的 [[Prototype]]。可以使用 Object.preventExtensions()、Object.seal()、Object.freeze() 或 Reflect.preventExtensions() 之一将对象标记为不可扩展。

¥Objects are extensible by default: they can have new properties added to them, and their [[Prototype]] can be re-assigned. An object can be marked as non-extensible using one of Object.preventExtensions(), Object.seal(), Object.freeze(), or Reflect.preventExtensions().

¥Examples

¥Using Object.isExtensible

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

// They can be made un-extensible
Object.preventExtensions(empty);
Object.isExtensible(empty); // false

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

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

¥Non-object argument

在 ES5 中，如果该方法的参数不是对象（原语），那么它将导致 TypeError。在 ES2015 中，如果传递非对象参数，它将返回 false，不会出现任何错误，因为根据定义，原语是不可变的。

¥In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError. In ES2015, it will return false without any errors if a non-object argument is passed, since primitives are, by definition, immutable.

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

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

¥See also

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