Reflect.isExtensible()

¥Syntax

Reflect.isExtensible(target)

¥Parameters

target

要检查其是否可扩展的目标对象。

¥Return value

Boolean 指示目标是否可扩展。

¥A Boolean indicating whether or not the target is extensible.

¥Exceptions

TypeError

如果 target 不是对象，则抛出该异常。

¥Description

Reflect.isExtensible() 提供检查对象是否可扩展的反射语义。与 Object.isExtensible() 的唯一区别是非对象目标的处理方式。如果目标不是对象，则 Reflect.isExtensible() 抛出 TypeError，而对于非对象目标，Object.isExtensible() 始终返回 false。

¥Reflect.isExtensible() provides the reflective semantic of checking if an object is extensible. The only difference with Object.isExtensible() is how non-object targets are handled. Reflect.isExtensible() throws a TypeError if the target is not an object, while Object.isExtensible() always returns false for non-object targets.

Reflect.isExtensible() 调用 target 的 [[IsExtensible]] 对象内部方法。

¥Reflect.isExtensible() invokes the [[IsExtensible]] object internal method of target.

¥Examples

¥Using Reflect.isExtensible()

另见 Object.isExtensible()。

¥See also Object.isExtensible().

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

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

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

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

¥Difference with Object.isExtensible()

如果此方法的 target 参数不是对象（基元），那么它将导致 TypeError。对于 Object.isExtensible()，非对象 target 将返回 false，不会出现任何错误。

¥If the target argument to this method is not an object (a primitive), then it will cause a TypeError. With Object.isExtensible(), a non-object target will return false without any errors.

Reflect.isExtensible(1);
// TypeError: 1 is not an object

Object.isExtensible(1);
// false

¥See also

• core-js 中 Reflect.isExtensible 的 Polyfill
• Reflect
• Object.isExtensible()
• handler.isExtensible()